Sunday, October 23, 2011

Interview: Drip Electronics

Thursday, September 22, 2011

A little on the Alesis Andromeda A6

From a thread.

Fri Jul 06, 2007 2:36 pm

Nice thread.

Brother Dave has indeed answered the questions well...and with a project this large, there can be endless questions.

Indeed, the Andromeda is the child of too many brews. It took over four years to create due to chip turn-around time (the first chips were pretty broken, and took a long time to iron out the S/H clocking and timing) and the size of the software/polishing the feature set. There were other products under development at the same time, such as the DG8 and the DMPro, that took up a lot of effort as well.

It's important to note that the Andromeda suffered resistance throughout it's development, sometimes subtle, sometimes to the point of near-cancellation. It was so deep and time-consuming, that there were those who wanted to wash their hands of it at various points. Folks like Dave, Julie, Dave Seaton, and others went to bat and kept it alive. A6 fans should offer thanks to them for fighting the good, continuous fight. Congrats again as well to Phil and Jeff for the killer developement/coding, and for the great ideas they added along the way. And again to Phil for putting up with me.

The sound of the A6 is not as large as a Minimoog, or a Moog Modular. I said this on the AH mailing list just prior to its release, that it won't replace either of those synths. Something about the 5V unipolar ASICs (3.3V effective operating range) changed the sound of the original circuitry. The filters were breadboarded and sounded pretty close to our vintage units, with as much variance from an original than any original shows against another (Moogs sound different from each other. I've heard killer 901b-based Modulars and deadly dull, fully cleaned and calibrated 921b-based units [at least in terms of oscillators]). Even the Chroma is larger-sounding than the raw, one waveform per oscillator A6 tone. Yes, it's been observed that you need to use tricks to enlarge the overall Andy tone. Thankfully, there are several ways to achieve this.

One trick I've had in mind (Mix Mode) is to use Colin's sub-osc@34.7 volume trick, with Osc 2 soft or hard sync'd to Osc 1, with just enough Osc 2 subosc to create a single, large waveform, effectively the sound of just one, larger-than-normal-A6-oscillator (can use Filter 1's HPF to track the fundamental with resonance to increase the size). Use Unison X and or Chord to "tune" another voice, having it act as a second Oscillator to the first. It would have to be the same overall Program, filter settings and envelope times, etc.

Route a satisfactory result out an Aux jack, into Voice 15 Audio In. Program Voice 15's Filters in parallel, with Filter 2 open and Filter 1's BPF at about 40-80Hz. Set that Program to the Main outs. This is just blue sky conjecture, but using the filters in an Audio In voice to mimic the Moog filters' seeming bass boost, as the resonance effectively shuts off down toward and past about 125Hz, is part of the early Moog sound. Of course, you'll have to use an envelope to Filter 2 Resonance or through the TG for the source voices...

And note... The very fastest setttings, in either 1.40.12 or the beta rev .13 are faster than the Modular or Mini envelopes. We found that the Minimoog VCA would click with an input voltage rise time faster than about 750uS. This might vary between Minis and with calibration as well, but the point stands; the Minimoog was not a speed hound. Use slower Engine Optimizer settings. This also cleans up the PWM some.

Obviously, the VCAs don't have the dynamic range that vintage units have.

Someone asked about calibration of the voice FM; Mic, was that you? Basically, the A6 has far greater depth of modulation than the Xpander per Mod route. Each Andromeda Mod route can sweep the entire range of its destination. The Xpander's control routes are limited to what, a minor sixth? I don't know if its FM is the same limited depth; I don't remember it having the out-of-control mangling of a modular with the route wide open. The A6 oscillator cross FM routes go way, way out into that territory. I know that there are oscillators that are stable enough to allow effective use of that sort of depth, but...why? This is a moot point unless you are using a triangle core oscillator ala the Buchla and Plan B designs. It's an entirely different way of flying, I believe the "Airplane" quote says. So, on the A6, only use the first quarter or so of the available depth, and you still may be well beyond the range of the Xpander, if you want to try to zero in on that sort of thing. And no, the associated VCAs are not attached to any code that would allow them to be optimized. I remember having asked about it, and it sounded both difficult and unlikely.

Want better PWM? Use an external hardware LFO through the Osc Mod input.

Has anyone used an audio-rate external LFO on the Filter input, with large amounts of resonance and voices going at once? Could be a delightful destruction.

If Elhardt is lurking, have you used my suggestion regarding the 1-16 Audio In, for violin body modification effects?

Regarding Marcus Ryle and Michelle... Dave, if you blinked, you would have missed the early engineering specification meeting they attended... As mentioned in the A6 Tips and Tricks document (a great thing!), the square wave on each oscillator has its own VCA. This is to allow a level blend with one of the sawtooth polarities, which Marcus showed to have a different sound than standard PWM. This is one of the things Marcus and Michelle gave us, and they may have helped Rob do some of the overall uP update planning.

Brother Dave, be careful with your prototype. Both of mine are now dead. It turns out that you can't do a reset on them; it wipes something out in the code (tuning tables plus???) Now it's down to you and Arnd. Regarding the prototypes using the rev 2 voice chips (production units use rev 3), the rev 2 had linear smoothing for the control signals, and as such, there is audible zipper noise. There are also some bugs that were fixed...but IIRC, the hard sync was a bit better than on the rev 3s. We needed the soft sync tightened, and for some reason, the hard sync might have suffered.

I still have a couple of light grey on grey front panels for sale. The thing about replacing the panels is not so much the 72 knobs; it's if you want to go the whole route and replace the far larger number of buttons. They sit tightly on their switches, and it's a bit of a pain to change them out.

I can't begin to imagine the effort required to replace the LEDs...

BTW, there are rumors that there may be differences between the red and blue Andys. The only difference is the color of the overlay itself. There are no technical differences. However, only 78 or so were sold prior to the bankruptcy, IIRC, not counting the first hundred or so units that went out to reps (don't know how many there were in that batch, or if there were any). We sent the remaining red overlays to Taiwan when then took up production, but I don't know if any further red units were produced. (And kudos to those who traveled to Taiwan to make sure that production was happening...that's effort...)

Thank Dave Bryce for the red units. It was his good idea.

Also, the chips didn't change at any point that I'm aware of; it is far too costly to run revisions for this to have happened casually. There may be variation in different pressings, but this is a subject beyond my ability to comment. Suffice to say, one major change that occured after the bankruptcy was the creation of an automated test fixture for the chips. It had been performed by ear and by hand by Jared and another gent at the old Hawthorne location.

Speaking of the Hawthorne location and the bankruptcy... When it became clear that we were losing the Hawthorne warehouse/assembly line/testing facility/parts stock/repair division/warehouse, Taiho and I went down and stripped it of all A6-related parts, and stored them at the then current location. We only had one A6 in-house through the bankruptcy, and we were still receiving calls from bands to get a hold of one... We had to keep it for reference, and to send to reviewers. Colin had been posting on TGS at the time, lamenting the extended wait for his already paid-for order... We built him one from the rescued parts, tested it, and sent it out. IIRC, there weren't enough parts to built two.

The folks who actually assembled the Andromeda at the US facility deserve much credit. It was a multi-stop assembly line, and the guys who set it up and wrote the assembly procedure have a major accomplishment on their hands. Thank you all! A few of us went down there every day for a while to help this process, as well as to assemble the first units shipped to the public (this is after tester units/sound design units/rep units). That joker FAST on AH has one of them, and it has my initials for quality control. A few of the engineers share in this; you don't know how many people kicked ass to make this happen. Some of use worked 80+ hour weeks at the end of its development, and some must have worked that much during it. Dave was one key to its existence; without a genuine keyboard person in marketing, several decisions might have been out of our hands. Dave and the project managers were very firm in defending it, and the engineers enjoyed the opportunity to basically do what had been specified without having to justify it every so often to those who didn't understand. It wasn't war, but when something is so close to your heart, you're ready to fight. Those who didn't understand analog synths, be they friend or partial foe, just seemed to leave us alone.

Dave has already explained the fights regarding the names on the unit on another forum. Dave was right, Andromeda is a great name for it. And oh, how hard we tried to find another that fit.

What would I change about the unit? If I could, I would re-engineer the voice chips to have the proper oscillator sonic oomph, a signal path with the punch of a modern analog such as the Wiard or Technosaurus, the filters to sound like the things they were genuinely derived from, and a modern uP to snap up those envelopes and raise the nyquist so that the LFOs could be opened up to higher rates. Anyone want to loan me a million dollars? I'll refund any available change after testing etc.

Speaking of the fabulous Wiard, I felt that it should have won Electronic Musician's Editor's Choice award, and IIRC said as much to the editor who phoned us. The Wiard 300 VCA/Env combination's variable slopes make for the finest power-shaping resource I've encountered.
God bless Bob Moog, over and over. He and a couple of other progenitors asked after working with us on the project; we wanted to keep most of it in our own hands, and thankfully, said progenitors went on to do their own new classics. We are sooo lucky...Peake



Sunday, September 18, 2011

Vintage Home Stereo Spring Reverbs

For your synthesizer/recording setup.


JVC Nivico Eca-101e (supposedly a re-badge of the Pioneer 101)

Pioneer SR-101 (true stereo, two short spring tanks)

Current pricing on both: $40-150.00


Pioneer SR-202 (stereo summing and input/output but only one spring tank).

Current pricing: $20+

These sound good, the spring is very small, 4" or 5" or so.

Found an example of the 202:

Bucket Brigade

If you're into that simulating reverb, should be fun to mod!
Don't know if it's a dual delay or a single BBD IC with stereo outs.

Pioneer SR-303

Current pricing: $30+

There are also Sansui springs and later Pioneer models (such as the 60) but I have not researched them and can't tell you anything about them. Some sellers on eBay are asking up to $400.00 for some of these and similar. Bwahahaha!

Although lacking in variable damping, no 17" tanks, or other amenities as found on say an Agonizer or the Modcan, here is your source for a DIY spring reverb module. Or two. Add switchable pre- or post- EQ...
I have an SR-101, and it's pretty quiet, but twangy.
DVD player straight into the SR-101- a little level imbalance and more noise than when I used it with the Selector. The source music is Drexciya.Obviously this unit must be modded to allow for wet signal out only:

Oh, and an interesting note found online:
"As a reverberation amplifier, it serves its purpose very well. But for those who just want to add a little "valve" sound to their system, it also works as a tube buffer stage. Turn the "Reverb Time" down all the way (removing the reverb tanks from the mix), and you have a nice cheap way to add a little tube warmth to your system for a pittance. The signal still passes through the tubes and it works out very well."
Davemoog wrote about the 101:
"The pioneer does funny things with the channels. They cross: Right drives left springs and v.v., So right reverb gets mixed with left dry, etc. so if you plug into the right you have to listen to the left out to hear the wet reverb signal. This works OK in stereo but odd with a mono input. It's easy if you wish to simply want L -> L, R->R to rewire the signals going/coming to the tanks."

EVOS Modular Synth

Sadly, never released. The phone number on the modules is likely not correct anymore. This post for historic purposes only, my apologies to Dennis if this is troubling in any way.

I have no problem with you passing on what I discussed with you. I will be

making some sort of announcement (sometime in early 2008) about the web site and when the updated Evos Modular will be available."....

The previous email:
Every few months, or so, I do some internet browsing, just to see what sort of things are going on in the synth world - especially concerning modular stuff. While doing so, I happened upon your post on the MATRIXSYNTH site (via AH).
It's always pleasing to me to know that people are still interested in my modular and also, that they seem to understand and appreciate what I was trying to accomplish.
While I have no objections to the documentation being disseminated, I often have mixed feelings about this. Firstly, (and most importantly) because the system has gone through a number of refinements over the past few years and secondly, republishing them only perpetuates the grammatical and typographical errors which appeared in the originals. To rectify this situation, I am (slowly) compiling data on the latest version which will appear in an upcoming web site dedicated to my modular system. Eventually, I plan to include some historical information tracking the development of the various versions of the system through time.
...I have been making plans to release the new version of the modular early next year. It will be, initially, limited to a set of what I consider to be the most essential modules, with gradual additions over time.
I genuinely want to see the modular in the hands of people who might put it to good use...
Take care.


EVOS Cabinet
High-resolution scans:

Friday, September 16, 2011

MS10/20/50 Componentry

This entry consists of thinking out loud about the MS series circuits and components thanks to the great PCB projects from EAS, available in the DIY forum. Thanks EAS! And thanks to Tim Stinchcombe for his amazing MS series pages and his thoughts. The majority of this is thanks to Tim. Thanks for putting up with my selfish musings, both of you.

The suffix on Japanese transistors seems to refer to specific behavioural ranges, so that you may select a FET with the proper Idss range and regular trannies with specific gain characteristics. Your circuit will function with components which operate in the specified behavioural ranges.

The Oscillator.

2SK30A (GR)

This FET is still easy to find on eBay and other places, and was used in everything from oscillators to effects pedals.

 Vgs range: -0.4 to -5.
Idss range: 2.6 to 6.5.

The BF245A covers the same VGS and Idss ranges but goes slightly outside of them as well, so it is a good idea to test and select ones in the desired range(s).
Vgs range: -0.25 to -8.
Idss range: 2.0 to 6.5. $1.00 each

2SK30A (O)

Got a batch from / Nikko Electronics. Good people, I recommend them. Thanks!

Vgs is between -0.4 and -5, same as the GR.
Idss range between 0.6 and 1.4.

Difficult to find! Didn't get a reply from XOX box parts suppliers. The Idss of this component is also evidently directly responsible for the square wave purity/duty cycle of the TB303 oscillator. I haven't seen a specific Idss measurement posted representing the purest square… I note that it appears in the first revision of the MS series noise generator as well.

The 2N4339 of Buchla fame (oscillators, frequency shifter, etc.) is similar. Vgs range: -0.6 and 1.8. Idss range: 0.5 and 1.5. These are very difficult to find, and even then, you'd need one with max Idss. Vgs could also be a little low…I've found some of these online for between $3.53 and $6.70 each.

I note that for some short time, Fairchild produced their own version of these FETs, with a KSK30 prefix. I have not been able to find these components anywhere. If you do, know that

2SK30A GR = KSK30 G (Idss of between 2.6 and 6.50 for both).
2SK30A Y = KSK30 Y (Idss of between 1.20 and 3.0 for both).
2SK30A O = KSK30 O (Idss of between 0.6 and 1.40 for both).
2SK30A R = KSK30 R (Idss of between 0.3 and 0.75 for both).

Check the datasheets to see if pinout is the same.

2SK and KSK are =not= available at Mouser, etc. 

TR1 2SA564A (S) or 2SA733 (K)


Image is from

The 564A is a better component than the 564.

"S" version Hfe: 260-520.

Pinout ECB Item A10402 2SA564A , has "S" suffix. Ten quantity averaged 350 hfe, right in the correct range. They have a mininum $10.00 order, so check out their ICs and such. They have 3046s hidden in the transistor section, for about $0.49 each.

EAS post that the 733 can be used here per the change to it in the MS50 oscillator. But it's a "K" version, high Hfe, between 300 and 600.

 I note that higher gain 733P can easily be in the 400 range as well. I got a bunch of high-gain 733P from Polida on ebay for $2.00.

2SC1685 (S), matched pair(?)

The MS10 Service Manual does not state if these components are special selected / matched. The "S" version of this component has a rated Hfe range of between 290 and 460.

Found some 2SC1685 on eBay and in looking closely at the item photo, noted an "S" on them…they are selling in batches of five; I bought fifty and from that, pulled several pairs matching both Hfe and Vbe, although the Hfes were on the low side of things, averaging around 320. Too bad if Hfe matching isn't important in the oscillator, I'm working on the side of "thorough" because I can.

That sale now shows a pic of a "Q" version, not applicable to this build.

2SC1583 (F) or (G).

The difference is in the gain charcteristic(s). F: Between 250 and 500 G: Above 400. Many of these on eBay show an F or G if you enlarge the item photographs, even though the sales listing does not specify "F" or "G".

This component is also used in the original TB303, so you know that the XOX box crowd have them stashed, if you can find anyone willing to part with some. I note that there is a warning in the XOX box crowds against 1583s with a "52G" on them; they may be re-labeled 798s. Check the Hfe to confirm or deny 1583 pinouts…and I see that one seller on eBay does indeed show the 52G, so take care as they may have gotten some from the same source. lists it for $4.11, but say that they no longer have it, despite their internet posting.

You can match a pair of transistors for this section if you have to, but in my experience, depending upon the circuit, you can end up with much lower performance results than if they are on a single silicon strata as with the 1583.

Two TL081?

I'm not using two TL081 as specified because the MS10 Service Manual shows that there is indeed an 081, IC4 just after the matched resistors, but half of a 4588 is used for the modulation summing, and a 4558 is basically a dual 741. So, a 741 will go there…DIY means each person can choose what they like. I've owned a few MS20s in my day and never found a problem with their tracking or stability so a 741 will be closer to this than other options.


 The 10uF electrolytic directly following the main FET might have audible importance, even if its purpose is a slight highpass function (1.4Hz according to EAS..Thanks!). I'm going to try Elna Silmic II caps here because I have some. Sorry, no Mundorfs :D

Worth considering as in this design, the sawtooth waveform is very nearly right out of the FET, only interrupted by the capacitor and a single level-compensating resistor, if that's its function. Nice, clean, gotta have it. No opamps there. The word "discrete" comes to mind, even though the rest of the circuit uses opamps. This part is just fine.


Is a 0.1uf non-polarized; there is only one .1uF listed in the MS10 service manual, a ceramic 25V. It is clearly visible in the following pic.

Mouser, 0.1uf 50V disc, 5mm pitch.


They have small multilayer as well.

6200uF Polystyrene

6800pF Mouser 23PS268 $0.37
(EAS say just play with init Fc trimpot a touch)


6220pf polystyrene capacitors, US distributor, $10.00 minimum:

(CPF) 006220R0AFAV 6220 pF 33v 1% $1.25


10uF / 16V? Listed as such in the 10, 20, and 50 schematics. Shown as the same size as C23 in this MS10 service manual pic, and shows as the same size as C22 in the pic.

MS10 Service Manual, both caps upper right corner:




1S1555 Diodes.

4) 1S1555 (D12 and D13 in the triangle wave circuit appear desirous of matching)

Tubeshunter on eBay have 1S1555 in large batches, but they are actually 1S1588, which are electrically compatable. These are also used in the DS1 distortion pedal.

Diode matching is said to best be accomplished with your VOM at DC voltage, ground to power supply ground, and +15V to a 100K resistor, to the diode to the positive VOM input. I haven't tried this yet.

These do indeed have a different rating than the 4148. Anyhoo, D3 and D4 in the modulation inputs / summing might be worth matching as well, if that sort of thing is very important to you.

Matched pair, 427R

The MS50 oscillator schemo does indeed indicate that these need to be matched. Grabbing 200 quantity 430R 5% as 430R 1% probably won't dip low enough…will select with VOM.

8) 100K point 1% (999,950K to 100,050K only).

Mouser 71-CMF55100K00BHEK

24 for three oscillators is $8.64.

It may be possible to use appropriate value trimpots jumpered across the resistor pads, if you don't have a VOM that can display five or six digits, or if you don't want to order .1% components. In that case, set the trimpots for the appropriate total K for each batch of resistors they are superceding. Turn the hopefully multiturn screw so the VOM jumps between 100,0 and 9999. This is theory, it is untried, so caveat emptor. Of course, you can use your ears against a digital synth for tuning reference.

Linear FM?

The jack at the base of the resistor chain/Scale switch is a hz/volt control voltage input. It would be interesting to use it as an FM input from another oscillator's audio out to see if it makes available some form or amount of linear FM. You could use these oscillators with a MIDI/CV converter capable of producing a hz/volt output.

Possible Oscillator Sync


"To hardsync VCO2 to VCO1 all you have to do is connect a diode from the Q4 collector to the Q10 base." (MS20 trannie numbers)


Note that I have not tested this, although I have confirmed that the correct transistor (EAS project nomenclature) on the master oscillator (1) is TR1 (collector) and on the sync'd oscillator, TR2's base.

The EM poster says that it's a bit uneven in locking which might mean that it could use amplification in line between the oscillators...which might also beg the use of a voltage divider to control the overall amplitude of that signal, if it would produce none through soft through hard sync...I have no idea if this would work.


The Filter

Thoughts on the original components within the Korg 35, make sure that your substitutes are in the same behaviour ranges. Here is a link to the beginning of Tim Stinchcombe's amazing MS studies. Wow!

And to the innards of the Korg 35 itself, thanks again Tim!


From here:

2SC1623 L-6.

The L-6 version has a gain range of between 200 and 400 Hfe. It looks like it requires a matched pair, Vbe and Hfe. Or one of those, or neither.

2SA812 M.

Being complementary to the 1623, it has the same gain range.

2SK94 X-2.

Has an Idss range of between 1.0 and 3.0. Vgs is typically -0.5, and overall range is between -0.13 and -1.5. The 2N4339's Vgs range is from -0.6 through -1.8. Its Idss ranges from 0.5 to 1.5. Conceivable to use, but must select for maximum Idss. The BF245A has similar lower range Vgs and Idss, but then goes way above at maximum values so you must select for both characteristics in the ideal range. J201 would have been nice but its Idss maxes at the 94 X-2's minimum, 1.0. In my experience with the J201 you won't find many at all in a batch going above about .90 or even up to / around that.

Link to circuit for measuring Vgs and Idss:

The 2SK94 datasheet can be found here, click the Technical Specs link.

 I note that it is extremely easy and very inexpensive to order reels of the 1623 L-6 and 812 M6. Surface-mount, just like in the Korg 35. The difficult thing would be to match the 1623s and the 812 to their gain as well. Difficult to measure surface-mount components… And the 2SK94 X-2 is available in surface-mount, but it appears as a slightly renamed suffix. I have no idea if it is truly a direct replacement with the same characteristics. Suffice to say, the easy availability of these components and their significantly low price for quantities in the hundreds, causes one to consider creating PCBs of dual filters. One per note for a keyboard. Like the legendary PS series.


The 2SC945K used in the VCA is a generic transistor similar to the American 2N390X series. It is likely the green-dotted transistor in the pic.

 The "K" version have a gain or Hfe of between 300 and 600. You'd have to ask Korg how they selected for this particular function, but it would be wise to have your transistor within this gain range. Use a socket if uncertain, and install transistors until you find one exhibiting desirable results, if there is indeed any audible variance. Then again, the MS10 service manual schematic lists it as a "K", whereas the parts list specify it as a 2SC945(L)K. I don't know if this matters as the parts list also reverses the "GR" in the 30A FET. Note that Fairchild had their own version, the KSC945, and it is available at Mouser. The suffix you'd want is "L", with an Hfe range of between 350-700.

Edit, Aug. 5th: Here's hoping that anyone reading this and popping open an MS to get measurements of the VCA trannie will do so and will post the results out of love of the instruments, love of sound, and love of music, and not out of any sort of destructive dominating urge. That only and continues to bring lower the entire field. Okay love you bye bye!

The Envelope

4) 2SC1685(S)
4558 (IC10 is not named in the MS10 service manual but is likely another 4558.)
10) 1S1555

The MS envelopes are desirable for two main reasons: The Hold function. Specific shape and rates. When I was at Alesis and we wanted two signature "Kraftwerk" snappy samples for the QS line, of quick envelopes hitting self-oscillating filters, we chose two: The Moog Modular as it was very fast and sharp, and the MS20 as it was slower at its minimum settings, producing a slight "wow" and a less-than exponential slope. Both very useful, with the Korg version being even more singular. I do not know if the filter/envelope slope is due to the envelope's shape or from the filter response curve, or some combination of both. It would be interesting to use these modules with other brand modules to make determinations.

1S1555, can use 1S1588, see Oscillator. TR5, 6, 11, and 12 are 2SC1685(S), see above. Found on eBay.

TR8 is listed as 2SA564A(S), and it is assumed that TR7 is as well as three of these are shown in the parts list. These may be a matched pair. If so, it would be a good idea to use 1% or match R42 and R43, 100K, R40 and R41, 47K D6 and D7. See Oscillator, available at for $1.25 each. C35, 6.8uf 16V is tantalum.


 I don't know why I'd never really taken a look at this classic LFO…one dual opamp, two matched sets of diodes, seven resistors, one capacitor, two potentiometers and an LED…and one unmatched diode in addition but who's counting. A 4K3 resistor is the oddest part. The capacitor is likely the 1uF 100V polyester capacitor listed in the service manual. This is simple enough to breadboard, and the variable saw/tri/saw function is cool enough to build more than one.

The MS50 Oscillator

Of course very similar to the 10 and 20's but has a TEMPCO and puts a couple of extra caps on the IC at the end of the Scale resistor chain. Also, the sawtooth waveform goes through an opamp here, possibly effecting that lovely character.

The MS50 Filter

Uses CA3019 diode array, rare and expensive, or you can match up some super-fast diodes. Also needs a batch of either eight matched or two groups of four matched (don't know if you can just use two groups of four matched) 1S1555 diodes. C16 is a big old 100uF / 3V tantalum in the audio path...? I'd heard that they aren't very good for processing audio... This filter has a nice, cold sine wave, great for making percussion sounds. However, there is a bit of hiss, if memory serves.

The MS50 Sample-and-Hold

Useful if patched with external noise sources and amplifiers because as-is using the internal noise source, you won't get an output hot enough to create a broad modulation range. Nothing odd here excepting the 2SK30A (GR) and 2SC1685 (S).

The MS50 Ring Modulator

Uses the very rare NJM RC4200 IC. IIRC, that IC was also used in a DIY LFO similar to the MS10 in that the waveform could sweep from saw/tri/saw, but was VC. If you can find any 4200s, that would be a better application.


Fairly simple, IIRC fast enough, only odd bits are four 0.1% 100K resistors, a 6.8uf tantalum cap, and a 1685 (S). Audio pots are used for the time factors. Three outputs of varios scaling and inversion...sweet.

The MS50 Hold/Delay/Attack/Release envelope

Don't remember putting this one to use...again, four matched 0.1% 100K resistors, two 1685 (S), one unnamed trannie (TR6), audio pots for time factors. Very nice to have scaled inversion outputs and a delay trigger output. Very useful if modded for 10V outputs.

The MS50 Audio Amp

Has an envelope follower and Schmidt Trigger output, very nice.

Thursday, July 21, 2011

The exclusionist, ego-driven allure of Vintaj(tm).

Some say that the Buchla and other rare systems are an attraction for the snooty.

In building a number of modules for a Buchla DIY system, and knowing that I can build as many for myself as I wish, say five dual oscillators, etc., I find that a certain mystery has indeed vanished but the excitement of actually being able to put in use, that much significantly cool gear is quite heady.

I don't care if I have to build it all myself. I don't care if it is only worth the time and effort involved, and if no one at all would trade a vintage module for a modern build DIY equivalent. It is simply gear that is too much fun for its own good. I don't care if I have to use balsa wood front panels and an empty air conditioner frame as housing. The intrinsic sweet of this gear is obvious, and it's an interesting journey to have to stare so deeply into the stuff behind the panel, even without fully understanding it. I know that the current Buchla gear far exceeds the vintage, but I have to build what I'm able. And no, I don't care if you have a bigger Buchla DIY system than I do. I'd just be interested in jamming together (chuckle).

Thursday, July 7, 2011

LF13331 and 4016 switching in the Buchla 292

The 292c uses semi-rare LF13331 switches (as do several vintage video games, which is where you can sometimes find this part) and Mark Verbos has done a version using the easily-available 4016 quad switch.

I haven't checked the 13331 specs but the 4016 is listed at .4% distortion. I wonder if any golden ears would detect such a difference (between that and a hardware switch)...

Wednesday, July 6, 2011

Errors in the CBS Buchla Schematics?

A thread at says that there is a mistake in the 194 fixed filter bank, and there is a mistake in the 106 mixer schematic (wrong capacitor value, confirmed in earlier Buchla 106 schematic). I'm wondering if there are purposeful mistakes in some or each as a means of dissuading other manufacturers from cloning them up, as Moog are said to have done with the 921b schemos in the Service Manual (after all, ARP earlier stole The Filter.). The Moog transistor matching jig schematic has a glaring error therein:

Bill and Will's Synth Moog Transistor Matching Tester Construction

Just something to be aware of if you're looking into building anything listed in this format, over at Magnus' page:

Magnus' Buchla Page

Saturday, June 25, 2011

Buchla 291 Dual Bandpass Filter Module

Thanks to Scott Stites, Luka, Mark Verbos, and others involved in bringing this design to DIY and of course to Don Buchla for creating it.

The Verbos design:

The thread presents a few variations on the Verbos design:

And Scott goes even further, discussing voltage-controlled resonance, etc.:

Marjan Urekar posts a clarified version of the original schematic with interesting notes:

Everyone gets rid of the selected 2N3958 dual FET, which seems to go for about $7.00 each on eBay as of this writing. I can't say if that effects the sonics of the module or not.

The original uses the 2N3566 transistor, kin to the 2N3565 found across the years in many places in Buchla designs. The 2N version is long out-of-production, and unless they get more, Mouser have just obsoleted the PN version of the 3566. I got a few...and it turns out that Mouser still have a lead-free version for 0.64 each:

One builder in the EM thread states that he first used the 2n390X and later switched to the 3566, finding that the 3566 is a bit smoother to his ears. If so, it would be good to have modules using each type of transistor!

So the overall news. I've built Luka's version, tested and enjoyed it, then gone ahead and began replacing things to more closely approach the original component list:

-Carbon Comp resistors (not all, don't have -every- type in stock
-PN3566 transistors
-Silver Mica capacitors for the .022 pair in the original schematic

I haven't compared this to one with all modern components but am seemingly aware of a slight change in the overall character; can't say if it's for the better or worse. Will have to do a side-by-side.

For those who have read "Blink" and validated its concepts, the "feel" of the 291 did indeed change with the substitution of carbon composition resistors, toward something less clearly defined. Will be interesting to see if this is the case sonically.

Again, why pursue slight changes away from modern standards? Because I've owned the original and like it just like that, and want to re-place exactly that.

What is it like?

This filter, like many Buchla designs, mis-behaves if you're expecting utter predictability. This is "character". Using the original BPF mode, you will find that the amplitude in the bass region is something like 12dB higher than the upper octaves. A sweep down into the bass will WHUMPH you up if you're not expecting it. And as you'd expect with vactrols, it's plucky and "acoustic". Although it doesn't close completely (30Hz being listed on the front panel as the minimum setting and the 12dB response means some pass-through even then), in HPF mode it will indeed go up and out to silence (the clever engineers at Korg in the early workstations with multimode digital filters simulated an HPF fully opening by allowing the Fc to raise to the point of instability/nyquist and then lowering the volume after that; sounds like an HPF opening all the way. Kudos!).

The BPF mode makes detuned-sawtooth synth strings very simple. The wide bandwidth cuts the bass but doesn't eliminate what you need in the timbre.

A very wide-ranging, great-sounding filter. You should have a pair or more in your setup.

Changes to the modified design

The modified design offers outputs for lowpass and highpass responses, and the luka layout adds voltage processing from a CGS design. It takes up nearly the same amount of space as the Verbos dual unmodified design, which is the size of an original Buchla PCB. I'm not a fan of stacking boards if not needed...

Tuesday, June 21, 2011

Buchla 106 Mixer

I've had a gent CAD up PCB artwork for a modified version of the late 1960s model 106 mixer. Again, I await Don Buchla's permission to publicly share this new PCB artwork; I will not do so without it. Here's hoping that he will; I would enjoy publicly sharing these builds with everyone interested..


Edit: I've recently posted the new schematic and new artwork here:


I have schemos of the CBS and pre-CBS 106 mixers. Off the top of my head, the only difference is a typo in the CBS version, C8, which repeats throughout the circuit (C4 and C11), and is correct in the other schematic, and that the earlier version states 47pF caps for C2 and C6versus the later CBS version with 5pF.

Due to the roll-off in the 10uF caps throughout the design, which I'm told is at about 70Hz per cap, I've opted for 100uF throughout, which should be ten times lower.

Each section of the mixer inverts, and I wanted each section (1-3, 4-6) to have both inverting and non-inverting outputs, for various reasons (inverting AC modulation/waveforms, resonant feedback loops, etc.). I have confirmed functionality for the regular sections and that inversion works and now have to determine the optimal gain structure(s).

As stated in the schematic, I used HFE matched PN3565 (cheap at I was hoping to use THAT transistor arrays but was dissuaded by the gent doing the layout owing to voltage differences. I do note that the THAT is used by Dustin Stroh (J3RK on and in his Verbos/258J build, for the last two 2N3565 which IIRC are involved with the square or saw shaping, and it works just fine.

I do not know if there would be any sonic differences in using other transistors such as 390X and BC55X types.

I also note that it distorts with even a single oscillator input (my 258B redo seems to have 1.7VRMS for that particular build, which is somehow above Buchla's nominal rating of 1.1). A CD player also distorts the circuit with the gain wide open. It =might= be a useful clipping in certain instances, but overall, is not immediately "musical" as some fuzz and distortion pedals at minimum settings.

I've had the 68K input resistors placed on-board to avoid lots of front panel wiring. It all fits on a single-sided 4"x6" PCB, which you'd expect from such a sparse circuit.

Why not go with a simple opamp circuit, which could also be DC-coupled for mixing control voltages? I wanted to see if the vintage, discrete circuit had any particular character (or lack thereof). It's too early to tell but yes, I'll later add a DC mixer circuit to this circus...

And I am indeed using AB resistors in all of the stated places. No photos as I don't own a camera or equipped cell phone.

Tuesday, June 14, 2011

Carbon Composition Resistors in Buchla Gear

The 258C seems to have random population of CCs, but the 258B schemo specifically indicates certain values to be carbon comp:

1, 2.2, 4.7 multipliers (10R, 1K, 10K, 100K, 10M, 2.2R, 2.2K, 470K, 4.7M).

In the last post I note that the 158A indicates that some resistors should be 10%.

"On the CBS schemo, note that some resistors are 1%, and some are specifically listed at 10%. These are at a glance, 1.0, 2.2, 4.7 multipliers, and include the 330K as well (which also appear in the sine shaper). Unremarked resistors are stated as being 5%. I note that the 258B schematic lists all 1.0, 2.2, 4.7 multipliers as being specifically carbon composition types, all others tin oxide. I wonder if you looked at a 158B/CBS/Tape Music Center unit if all of these would be Allen Bradley or other carbon comp."

I also note that the CBS 106 mixer schematic lists many resistors as 5%, and the rest as being 10%. Again, these are the 1, 2.2, 3.3, 4.7 multipliers (1K, 10K, 220R, 2.2K, 330R).

I've asked a 158 owner for a pic to see if they are there...

If you are on or other higher-end gear pages, you will note that carbon composition resistors are spoken of highly. I note that on audiophile DIY sites that it goes further, with tantalum resistors being the item of choice in certain critical places in the signal path, especially in circuits with gain as it is said that tantalums have no thermal noise, as do metal film resistors. Then again, tantalum resistors seem to start at about $3.85 each, and go up to around $10.00 each.

I note that since these are vintage components, they can suffer from slight oxidizing on the leads. A slight rub with loose steel wool right up at the resistor body will clean these up quickly.

Saturday, June 11, 2011

Buchla 158A, 158B, 158 CBS versions

A thread in the DIY forum brings up interesting questions:

The CBS version up at Magnus' Buchla Page is extremely similar to the B version.

A version:

-All discrete, no opamps
-No uA726
-Transistors: MD708B (dual), 2N4916, 2N3565, U147, E101 (E101 is selected for =approximately= .5 Idss).

The E101 also appears if I remember correctly in the Minimoog oscillators, and the U147 also appears in the earliest versions of the Moog 901B oscillator.

B version:

-Opamps: LM302, LM301A, uA726
-Transistors: 2N4916, 2N3565, 2N4339 (Idss between .7 and 1.2), 2N4339 (Idss between .5 and .8).
-D1-D3 are listed as FD111 (???)

On the CBS schemo, note that some resistors are 1%, and some are specifically listed at 10%. These are at a glance, 1.0, 2.2, 4.7 multipliers, and include the 330K as well (which also appear in the sine shaper). Unremarked resistors are stated as being 5%. I note that the 258B schematic lists all 1.0, 2.2, 4.7 multipliers as being specifically carbon composition types, all others tin oxide. I wonder if you looked at a 158B/CBS/Tape Music Center unit if all of these would be Allen Bradley or other carbon comp.

As mentioned elsewhere, and thanks again to J3RK, the J201 transistor, easily available, has an Idss range which falls easily to .5 or so. I'd love to learn about the others and what would sufficiently replace them. The 2N4339 doesn't seem to dip down into that range very often; my batch go down to about .66 as a minimum. Useful for the 158B..

I note on the 158A part layout document (5Apr68) that there are a few bits not mentioned in the schematic:

-Note- "Plug in" version.
-R8 Sine: 1.5K; Harmonic: 680R.
-Add R34, (other notes, too distorted to read)
-No C7

There is a fat pen mark at the upper right, stating 158A-L.

I don't have the schemo in front of me so I have no idea of what "harmonic" means.

Wednesday, June 1, 2011

Oscillator Drift Iteration

Ye Olde Oscillatore Drifte question...

The Buchla 258B, with the 2N3802 dual transistor in a single package and the uA726 heated transistor pair (again in the same package/substrate) provide a very decent amount of pitch stability without going into the land of totally uninteresting. I wanted to see what component variation would cause/effect.

This especially centers around the removal of any dual transistors in a single package. Using modern transistors, matching isn't terribly hard for the 1% and better range, but not having them in a single package/substrate provides for less overall accuracy. Having them physically contacting each other with heat grease can improve things but in some designs such as the Moog 901a/b, these transistors are not placed close enough to each other to allow for physical contact.

Individual transistors with no physical contact per pair seems very important.

-The 726 and 3802 I have replaced with selected BC550C and 560C and of course, find myself in maximum driftland. Adding a TEMPCO noticeably reduces this but does not eliminate it. Might be nice to have a single module set up this way. Didn't even bother to heat grease them together to see if slightly less drift could occur.

-Tried a TEMPCO plus uA726 plus 2N3802 and it powers up and STAYS there. "No, too much!" -The Who, "Magic Bus", "Live at Leeds"

-I note that the J3RK/Verbos 258 design using the THAT340 is stable enough without a TEMPCO. I hope to have a future iteration of the 258B design using a THAT340 to replace both the uA726 and 2N3802. I would have pads and components added so that you can use the vintage parts instead, if desired.

The J3RK design uses the second half of the 340 IIRC to replace the 2N3565s. A tech tells me that the THAT has a quarter or so of what is needed to correctly operate in place of a 3565 pair...could be interesting to compare how 3565 and THAT versions sound/look on a DAW.

-There is indeed a certain solid "feel" to the uA726; it grabs the pitch nicely but not absolutely.

Sunday, May 29, 2011

Buchla 258B Remake Project

This page will be a work in progress just like the build itself. I anticipate at least one more revision of the PCB.

Please note that Don Buchla has not replied to my emails regarding this project and sharing the new PCB artwork publicly or in any way, so at this time, it is not for anyone except myself; I hope that these notes are helpful to any interested in such things. To the destructive people reading this, please go and do something positive/constructive instead. HA! Okay love you, bye bye.

I have had a gent create new PCB artwork/layout from the Buchla 258B dual oscillator schematics. I've once owned this version of vintage Buchla module and prefer it over the later "C" version as the "C" is a bit too stable.

Added to the original design:

-L-1's 3PDT switch for selecting square or saw for the Waveshape section (added to the sine at the main output). Works just fine; can also simply install jumpers to hardwire one of the two types. Very clever, very fun. My preference is always sawtooth and I would have built all of my oscillators as such, but with the simplicity of a switch, I'll certainly now be using square waves to see what I can see. I envision Buchla Dub music (grin). Kudos to L-1!

L-1's drawing:

-Triangle output buffer. The triangle is a great addition to this build. Can't wait to try some exponential FM with them. It is however separate from the main output so it currently cannot switch between sine/tri. I had hoped to be able to switch between the sine and this triangle, in the main output signal path and not have it as a separate output, thus avoiding repatching etc.

Keeping with the original:

-Using 15uF Kemet tantalum capacitors for decoupling the positive rail, only. The original has no negative rail decoupling.

-Kemet 1uF tantalum capacitors for the exponential FM path.

-Carbon Composition resistors. The schematic states that all 2.2, 4.7, and 1.0 multipliers should be carbon composition resistors, 10%. This includes the (sole 1/2W) 2.2R and 10R power couplers, the 2K2 and 470Rs in the audio path at the Saw/Square selector, the 470K and 1K 1% in the CV section, a couple of 10Ks, and the 10M and 4.7M on the front panel CV and Fine pots, respectively.

The 1K 1% and IIRC a 100K 1% are a problem; I've just received 100 quantity 1K 5% and only two were just at 2%, and all were above the nominial 1K value, not above and below. No joy there, but the same effect allows a pair of 470K(-ish) resistors to serve as a 1K 1%. Two 47K should provide the 100K 1%.

I note that early Moog oscillators have CCs littered about seemingly randomly, comparing module aside module. This might have simply been an issue of supply at the time they were building. The parts bin may have just had both types of the same value. The pic of the Buchla 258C circuit board in my recent "Vintage Parts in the J3RK Build" post on this blog shows a number of CCs, but neither 258C schemo I have states anything about certain values being part of the design (or not).

Swapping out the 470Rs in the sawtooth circuit gave the circuit, to me, a slightly better feel. I don't know what change in sound will occur, but I note that guitar amp and high-end tube EQ and compressor builders swear by carbon comp resistors. Me, I do use my sense of "feel" in selecting music gear. I have made some good desicions, if anyone is interested. Having been screaming about Buchla gear for perhaps two decades now... It certainly goes far further than that, but that's a topic for another blog. I'm just sticking to Don's delineation.

Why be anal to any degree regarding such things as obsolete, badly-behaving tantalum capacitors? Again, I've owned the original and who knows what combination of items contributes to the's not for me to say, but I am interested in further knowledge if it shows up.


The uA726 and 2N3802 are becoming Unobtanium Siliconis, and the 2N4339/2N4341 etc. are as well. I note success in the Verbos/J3RK PCB project in applying J201 for the 4339 and MPF102 for the 4341; will one day build one of these dual oscillators using them.

Pads/Switching for the uA726 and TEMPCO resistor

It shouldn't hurt a uA726 to have the heater leads (positive and negative 15V) run out to a DPDT switch, and another switch between a regular 2K resistor and an equivalent TEMPCO, for those rare times you actually want an oscillator to not move. Combinations of these should be interesting...

Control Voltage Response/Scaling

I'm told, haven't confirmed, that the original is 2V/Octave. My first version and etchings are this design.

Linear FM

Listening to the J3RK board, I find that having eschewed the 258C's linear FM has been a mistake. It's not like linear FM on other oscillators, and I should have known this from the "Buchla" name alone. Will determine the correct connection to add this to the "B" design.

Stronger Exponential FM

While checking the 106 mixer outputs for inverting/non-inverting behaviours, I bypassed the standard FM in and merely clipped an amplified oscillator output to the positive modulation input of another. The modulator was sawtooth, the carrier sine. It produced, when the pich of the sine was swept, an effect slightly similar to sweeping the clock rate of certain digital noise sources, most commonly heard in the 1980s video game Tempest when leaving one level and approaching the next, the legendary Atari POKEY integrated circuit. I am very happy to have "stumbled" upon this and will likely add a switch between "normal" and "depth" exponential FM, probably adding a 1R or as required to avoid shorting to ground at zero index.

More Waveforms

The J3RK build offers a pure square wave ripe for buffering, if one is interested in having another "perfect" waveform in their system, as opposed to the mutant square available at the main output. I'm interested in the partial saw wave as depicted in the Verbos schematic. And having it and the triangle on a switch to interrupt the sine at the main output. Perhaps even the pure sine waveform found at the sine shaper FET, but all would have to be selectable to the main output, not as individual outputs.

Thursday, March 31, 2011

A touch more on the spiritual and musical

"Consciousness, Anna translated. Group consciousness. Well, was that so strange? She had felt it more than once on stage, when a group of dancers had transcended what they were individually, had become a unity moving to the music in the creation of beauty. Such moments had, for her, taken the place of religion."

-"The Erdmann Nexus", Nancy Kress, 2208 Hugo Award winner for best novella.

This is the same as when a group of musicians hits "chemistry" and all know where the entire thing is going, and interweave and contribute in accordance, effortlessly. The same thing as when an idea appears, a moment of clarity. These are examples of where humans tap into what is...higher.

Can something as simple as a piece of music equipment even begin to exhibit such characteristics, or better, inspire such perception in a user?

"Carrie, have you ever heard of the principle of 'emergent complexity'?" ... 'Emergent complexity' means that as an evolving organism grows more complex, it develops form. In other words, teh whole becomes greater than the sum of the parts. Somewhere along the line, our primitive human ancestors developed self-awareness. Higher consciousness. That was a new thing in evolution." -Erdman Nexus

Of course I don't expect a piece of gear to soon gain self-awareness, but certainly, those with a higher perception of the -whole- of an instrument, of parts interweaving into something greater than the whole, provide us with something that should be experienced and cherished.

Thursday, March 17, 2011

Vintage parts in J3RK's 258ish clone

Why not use original Vintaj Partz? It's not as bad as you'd think, and in one instance saves you a lot of money over a certain vintage part replacing an inexpensive original, and at one place, seemingly recommends against the expensive vintage part. Also find tips on adding Exponential FM, switching between saw and square waves, etc.

I'll be editing this as I learn more about the build.


Diodes are Fairchild 1N457A, seven cents each at Mouser:

A matched pair is required in the sine shaper section of each oscillator so get a few when you order. (Honestly, none of Don's oscillator schematics states that these components including the associated resistors need be matched or even 1%, but what are you gonna do.)

PN3565 transistors are 21 cents each at Mouser:

A matched pair are required. Note that the pinout is left to right EBC. They are Q7 and Q8 in this project. Not needed if you're using a THAT340.

Q9, a PNP transistor. Originals use a 2N4248. Available here for 20 cents each. I don't know about minimum orders. Second from the bottom.

If I remember correctly, this is only used for squaring the output of the core.

Sine shaper JFET, Q10:

The original uses a 2N4339; rare and expensive, especially since you'll have to get enough to select a correct Idss value.

The J201 and 2N4339 indeed have similar but not exact Idss ranges, which is the important bit for the sine shaper. I bought 30 J201 off eBay and got two with an idss in the .8x range, four in the .7x, and the rest were well below that, in the middle of its indicated range. Buchla specified the sine shaper as requiring an idss from between .7 to 1.2, "preferably" .8 to 1.1. I find that .8 and up is just fine for this transistor.

I've since purchased 200 J201 and found only one with a .90 Idss value, and none higher. It can max out at 1.0, but I didn't see any near that. The J202's Idss range is way too high for even a few to fall into this required range.

The 2N3819 is way higher than this, even for its minimum which in one datasheet is stated as 2.0; you may find interesting distortion waveforms from this...

Results of replacing a selected 2N4339 with a selected J201:

The J201 ends up sounding pretty much the same as the 2N4339. The 2N4339 just feels "stronger" in this circuit, however. Yes, these things matter to me.
But obviously, the J3RK-recommended J201 will provide a sine-like result (though never perfect from this particular oscillator) for cheap, compared to purchasing several 2N4339 and selecting a few usefuls!

I can post that at the far end of the purity trim, it does sound different with the J201; it becomes a rather thin square-ish wave).

Test rig for determining Idss:

Or more simply:

-Alligator clip the + VOM lead (set it to DC current) to a 9V battery's + terminal
-Clip the - VOM lead to the FET's Drain pin
-Clip the FET's G and S pins together and on the other end, to the battery's - terminal.

Ignore everything in the above PDF below grounding the transistor's S. In the diagram, "ground" is the negative battery terminal. A milliamp meter, one 9V battery, three alligator clips, and you're in business. D goes to the milliamp meter; G and S go to the negative battery terminal; a single clip to both leads is fine. The Fairchild J201 I got off eBay have a pinout of DGS, so I just pried out the D pin a bit and off I went. Be careful. I managed to connect the wrong leads and burned out a 2N4339 just like that. Got VERY hot, then didn't measure Idss at all. sadface

Switch for selecting Square or Saw waveforms

You'll see some "Square/Saw" resistor seating on the board; the originals had one of the dual oscillators set up as a square wave, the other a saw. J3RK provides a choice for every oscillator you build. Kudos!

This is for a waveform that is added to the sine wave, by turning the Waveform pot and/or by connecting a positive CV to the Waveform input. The result is, on a scope or DAW, NOT a perfect waveform. This is not a problem. It doesn't sound imperfect, it sounds a bit more beefy than a "pure" saw or square. (You can tap the pure square waveform, regardless of what you stuff in the "Saw/Square" sections, from a pad on this board intended for just such an emergency. It requires a buffer but that's what the MUCK is for.)

If you wish to have a switch between the "dirty" saw and square that are controlled by the Waveform pot and added to the main output, try this, it's confirmed to work. Thanks to L-1 over at's DIY forum, who posted this; a very clever catch. I'd stared at the 258 schemos for years and never made that connection. L-1's post and pic are found here:

Full instructions are found on page 6 of the Muffwiggler build thread. Please see that page for a handy wiring diagram by emdot ambient:

3PDT switch (be careful that you keep the saw and square "sides" separate as the switch will likely move around enough to require color-coded wiring etc. to maintain easy trouble-shooting). Mine has connections engaged per a lever fashion; when the switch paddle is down, the center and the upper connections are engaged, whereas a slide switch would show a 1:1 positional result.

As the switch itself is fairly deep, requiring a certain depth of front panel standoff, I've simply stuffed resistors standing up, or perpendicular to the PCB. Don't forget a bit of heat-shrink tubing for these connections. I just cut the resistor lead off to about 1/4" and solder the wire to it; I didn't twist the wire onto them.

Switch 1 connections, "Saw/Sqr 0 and 1".
-Left pad of the "0" has a 150K to the switch Saw side.
-Left pad of the "1" has a 330K to the switch Square side.
-Either of the two pads on the right, which are connected, at the 68K, out to the switch center.

Switch 2 connections, "Saw/Square 2 and 3".
-Left pad of the "3" has an 820K to the switch Saw side.
-Right pad of the "2" has a 680K to the switch Square side.
-The two center pads are used for the switch center.

Switch 3 connections, "Saw/Square 4".
-Two resistors are mounted in the bottom pad, a 470R to switch Saw
-and a 2K2 to the switch Square side.
-The top pad at the 680R is for the switch center.

Cheap 3PDT switch, the ones I'm using:

Exponential FM.


Audio in to a 1uF tantalum cap (positive away from the input) to a 33K resistor to the 50K audio taper pot to the CV summing path. It may be possible to use one of the J3RK "1V/Octave" inputs for this path, obviously losing the 100K resistor specified there; I'll report my results when available.

You can add this via a swich after the 50K audio pot if you mount the tantalum cap and resistor at the front panel; switch out to the Linear FM input (jumper the cap and resistor) and also at the Exponential CV Control/Sum input. It's just another input at that point. Provides true chaotic character when two fairly high frequency oscillators FM each other. Zero capacity for keyboard tracking with recognizable pitch here, but many, many sounds are available that to my knowledge no other oscillator will produce, in terms of going from a sine out to pitched noise in a single knob change.

It is seen here at the far left of this schematic, of the earlier Buchla 258A:

I do note that when I attempt this, the results are not what I attain on an original or on my "clone". This is likely due to the fact that the old version has a CV sensitivity of 2V/Octave. It is worth considering the addition of a gain stage, especially one capable of some 10X or more, as the original version produces far more wicked expo FM when driven by such a gain stage...and this is what has been putting me off from finishing my J3RK clones, this lack of original character exponential FM, which is my most important function from this design!

Exponential FM path values.

Note that the last version of the Buchla 258 (the "B") prior to the "C" upon which this is based, used a 1.0uF Kemet tantalum capacitor and 33K resistor in line prior to the amount pot (could also of course be after). This is for the exponential FM.

I'm currently experimenting with expo FM and have so far not gotten the results I'd expect. Working on it, will post.

Linear FM variations...

There is a schematic not on the web which comes after the common "C" schemo, and there are a few changes. See also the circuit board photo below. One of interest to J3RK builders are the values in the Linear FM path: a 4.7uF Kemet tantalum capacitor (of course try WIMA poly, etc.) and a 68K resistor. J3RK's silkscreen calls for a 10K resistor; find out what you like.

Integrated Circuit Variations

741 Integrated Circuits were used in the original for CV summing and all other ICs, but here only the two output ICs are the same as the vintage version. The 741s dark character is useful when doing chaotic FM via sine waves, two oscillators exponentially FM'ing each other at pretty high frequencies. Would likely be too bright if using a TL071, but you be the judge. Not sure how much difference it would make on something like a saw wave. I obviously hope that a 741 in the CV summing will provide a modicum of inaccuracy per the original.

Here is the parts side of a vintage Buchla 258C, from which this hybrid is drawn:


If you are anal about making your mutant 258 more like the original, here are some hints from the photo:

-Note that the 220pf is the light brown ceramic at the bottom outside. Types other than ceramic might not produce any sort of audible difference.

-The 10R 1/4W and 2.2R 1/2 at the power supply inputs are Allen Bradley carbon comp. Mouser now has a carbon comp resistor supplier:

-Note that the 258B actually specified carbon comp resistors at certain other places in the circuit, including the 2.2K and 470Rs used in the square/saw selection, respectively. All 2.2, 4.7, and 1.0 multipliers were supposed to be carbon composition resistors, 1/4W, 10%. Says so right on the schematic. This of course includes the 2K2, 470R, and on the 258B, 4.7M, 10K, 1K (selected for 1%), etc.

-The original used a single 15uF Kemet tantalum capacitor to bypass the positive supply rail; none were used to bypass the negative rail so far as I know. It is visible as the horizontal silver piece just above the second IC from the bottom, sitting at the outer edges of the board.

I have used 15uf electrolytic for positive supply bypass in my mutant build and stuffed nothing into the negative bypass cap setting, as the original only had 15uF positive rail bypass.

-75% of the ICs were provided ceramic bypass caps (.01 on the 258A). I don't worry that there are none on the mutant version.

-The large resistors on the original are 1% type, with the rest being 5% or so, and a few carbon comp as well. Where 1% is not specified, I'm using 5% unless I only have 1% "in stock". I note that the Bucha 258B actually specified certain resistors be carbon comp. I'm not bringing that into my own mutant 258 build, however.

-The large vertical silver pieces at the top outer edges are the tantalum Linear FM caps. Note that your mutant build boards specify a 15uF electrolytic caps. No problem, go with what sounds best to you, but note that a 4.7uF value is depicted. The board picture is of a later version using different values.

Be sure to thank J3RK for the great project! And a silent thanks to Don Buchla and Mark Verbos!

Wednesday, January 26, 2011

Variable echo times from fixed-motor reel-to-reels

Some reel-to-reel recorders do not have DC-driven motors and as such aren't easy to make into something with variable speed, hence variable delay times when set up to do echo. Others do, but you might not want to mod them.

Place a musical-sounding digital delay (Lexicon LXP-5 and others) at the input and route/mix the return/feedback into its input. Viola, variable-delay tape echo =character=, but the feedback will sound a bit different and you won't be able to do analog delay time modulations. Digital distortion also of course factors in so a limiter at the input might help.

Please to experiment.

Thursday, January 13, 2011

A bit more vintage from your JH Living VCOs

JH: "I've never heard better drones than from three EMS VCOs running at almost the same frequency, and beating against each other in an ever changing pattern."

I've owned VCS 3s and Moog Modulars, and the early Moog oscillators, drifting away, outdo the EMS for a musically interesting varying tone. I don't mean out-of-control, but as he implies, something that is pleasing to hear.

If you want "more" of that from your LVCOs, consider installing a switch for the oscillator core capacitor, as the EMS (and even the Moog 901b) utilize vintage Mullard mylar capacitors, not polystyrene/polycarbonate.

C3, 2.7nf, is the polystyrene core capacitor, yes?

How to? This applies:

"Ideally, each Oscillator should have the two capacitors on the pcb joined at the current input end, to keep this sensitive point a short path. Fly a screened twisted pair cable wired to the other end of each capacitor to a panel switch such that it switches the larger capacitor in parallel. Ground the screen from a nearby panel control. "

"I've chosen the same noisy 4-transistor exponential converter that EMS used in the VCS3. I'm not overly scientific about it - I just like the sound of it."

Then why change anything at all about it if it sounds good as it is/was?

Adding the less-accurate cap may increase liking the sound of it- it's up to you. I remember Dean Hinton's original EMS mods page mentioned that its lowly vintage power supply had something to do with the "bad" behaviour of the instrument; you may wish to use a less-than-Kosher power supply to help regain the desirable character...I also note that when I sampled a VCS3 all those years ago, that the tip of each sawtooth waveform had a different overshoot, meaning that each cycle was slightly different. I don't know how that will turn out at audio frequencies but it has to be yet another aspect of Difference from the modern. I don't know how to re-create this, or if it is the same on all EMS oscillators. (I posted this at TGS many years ago; someone took my statement incorrectly, imagining that I meant that I could somehow hear each wavecycle at audio frequencies, and differentiate them...certainly not the case, but you can see the difference in a sample. I'm not sure about the cycle-to-cycle homogeny of the LOs, but it's worth considering.)

You may want to make sure that it has the same exponential .32V/Octave response (or so) for deep exponential FM.

Also, part of an interesting drone/its overall interesting character may be Oscillator 3. It doesn't, in the several images I've seen online, have 2C746 matched, single-housing trannies, which aid in heat transfer/stability. The 2N5172 pair which appear to be used in its core instead of the 2C, are sometimes (perhaps always) epoxied together without heat-transfer compound. This may produce more drift than the same oscillator with a 2C746 or other matched, single-housing pair.

"Back to the crow, back to the stone age!" -March Violets. Yes, I'm suggesting that on at least one of your LOs, that you install a matched but heat untreated pair. All of your oscillators don't have to sound like a bomber squadron, but one with a bit more drift will increase interest and perhaps get you closer to what sounds good about the original. Consider two-oscillator patches and use the third oscillator for FX. Sometimes, use all three for the different character. The Minimoog is also set up in this manner, however its Oscillator 3 is likely (haven't looked) of equal stability as the first two.

You can also put the Tempco resistor on a switch, DPDT, to select between it and a resistor of the same measured value but standard carbon comp or metal film. See the above link and considerations per switching core capacitors.

But of course, just ignore me; no one actually likes those old instruments or why they sound and act the way they do.

And to those who leap to fear any time I discuss the facts as I am learning them, get a life. Just get a life.