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.