Thursday, June 18, 2015

Cleaning tip for vintage stereo gear

A medium bristle toothbrush. It alone is plenty to dust along edges and around knob, switches and buttons. Use with warm, possibly slightly soapy water on tougher items:

Left, after cleaning; right, before.






After brushing with warm, soapy water.



Sadly the display is plastic, not glass, and someone got packing tape across it and the glue had long since caused the plastic to bubble. Uncleanable.

After some care and cleaning...there are still scratches and bumps but it's finally clean:



Salvaging the Polk PWS110 Subwoofer

The plate amp in this model may unfortunately be faulty. Wire the driver directly to a set of the banana jack inputs and power it with an external amp. Both loud and punchy, which more of a pleasant anomaly than you'd expect.

Wednesday, June 17, 2015

Audax HD100D25 Tweeters

Used in the legendary Spica TC50 loudspeakers. I've found that they were also used in a Californian speaker from the "Lancer" company, a 3-way with 12" woofer bookshelf type which have to have been from the same time period. Useful to know of a source for potential harvesting...and I don't mean the JBL Lancer speakers or the early Lancer speakers with classic coaxial drivers, etc. I can't even find photos of the things through different searches.

Thursday, April 16, 2015

Don't just power up vintage equipment after years of storage.

We all know because of power supply capacitors aging etc., to put them on variacs...but there's more. 17 years of storage did this to a friend's Marantz receiver:

17 years of storage

17 years of storage 2

It's beginning to look a lot like Christmas...time for the toothbrush and performance duster spray all came off but WOW.

Wednesday, April 15, 2015

Cheap and easy excellent tube amps


The Akai M-8 reel to reel and its re-badged versions (Roberts 770) happen to contain a completely independent pair of very high-quality tube preamps and amps which may easily be removed from the original case and with the addition of one cap value between two points, be turned into really excellent low-power single-ended tube pres/amps. The current price of these units in great condition is around $300 and you can find them for much less as well. Many of them were manufactured and I've read that many were brought to the States by soldiers purchasing them while overseas.

Mind you, we're talking 4 watts per channel at 8 ohms, but if your speakers are 90dB efficient for 1W/meter or 2.83V, and you sit near them at a desk (less than a meter from them), this is a superb project. I'm talking no hiss or hum, and the pre can be used for recording via the headphone out. There are another pair of pres in there, for phono (lacking RIAA correction) and for the tape section, which may also be brought out separately. The pre and the amp can be overdriven for special effects when recording.

We're talking single-ended design, known as being very clean and musical. Modern enthusiasts have discovered the 2A3 and rediscovered the 300B triode and there are many kit and boutique amps utilizing them from decware, tubelab, and more. 2 to 8 or so watts per channel, called "flea powered" amps, but with real detail and musicality. I built a solid-state Chipamp using tantalum resistors and it sounds fine, extremely quiet, etc. at some 70WPC. After getting these amps up and running, I've boxed and forgotten the Chipamp, only missing it for those times I really want to peel the pain off the walls.

If you use a subwoofer and highpass the audio input into these amps, 4 watts above say 150Hz or higher will be more than if loading them with full-range signal. Will be attempting this at some point.

Don't be fooled by the unit in stock condition; monitoring the Mic/Line inputs through the Speaker outputs (all 1/4" jacks) will result in quite a treble boost which is pre-emphasis for the tape section. A couple of high-voltage Mica caps totalling 375pf (used 220 + 150, parallel) across two points flatten the response (and the tape speed tone selector's 17/8 IPS setting will then provide a slight treble boost. I imagine that you could use a switch to bring in and out one of the caps which reduce the treble pre-emphasis, to act as switchable treble boost controls if you need more than provided for with the 17/8s switch.

Instructions on the net regarding disassembly come off as more complex than what I found to be the reality. Perhaps my unit was a later version because no wire clipping was required whatsoever for the basic removal and use modification. There are several multi-pin plugs which must be removed between the amps and tape section, as well as a pair of RCA jacks. One set goes to a DIN jack on the side of the cabinet; I believe this is to tap the phono output...I'm not sure as I've not concentrated upon that part so read up. I've simply disconnected it.

If you're stuck with less than 90dB efficient speakers or have a large listening space, remember that the speakers of yesteryear were designed to be loud when used in combination with such small-wattage tube amps, as are often found in vintage stereo consoles (another goldmine for tube gear, can sometimes be found for very cheap...I missed a Grundig with a reel-to-reel for $30 a few months ago).

Pioneer made a line of highly efficient speakers for hobbyists at one time, the PAX series, which save space and add to coherence by virtue of coaxial mounting. Although the frequency response of most of them will leave you needing to add a graphic EQ in order to tame them, we're talking 100+dB speakers. Put them in a 1/4 wave enclosure or full transmission line...even though they're not indestructable (20 or 30 watt limits), it'll do. Altec also made significant highly efficient coaxial designs if you're super serious about this. One company is even re-manufacturing them at the time of this writing. (Great Plains Audio.)

It bears stating that this preamp/amp combination does not impart some magical glow upon the signal. It's also not overly crisp. It's not "warm" because the treble is slightly rolled off. It just gets out of the's lacking some things which are unpleasant about less well-designed solid state gear.


Applying "audiophile" concepts to a pair of DIY speakers

When I was living with less means than today, I'd found a pair of Infinity bookshelf speakers with rotted woofer surrounds. I found a pair of Peerless Nomex 6.5" woofers at which fit the cut-out in the speaker cabinet. Being a fan of AMT and similar high frequency drivers, I found that the BG Neo 3 planar tweeter. Had to cut out an opening for them, however as they are significantly larger than the dome tweeters which came with them. Since my holes were not symmetric, I used modeling clay to seal off the inside. The cabinets are unported, are fully sealed.

This is well and good; I found some Infinity crossovers with "cups", or the fitting containing the speaker wire terminals, at a surplus store for only a few dollars. Hooked it up and it sounded fine, no distortion from a tweeter crossover too low in frequency, etc. Absolutely ludicrous to cut-and-paste a two-way crossover with drivers different than that for which it was designed, but the ears are the final master and mine said "fine".

The story does not end there...the crossover had ten cent capacitors, white sand-encased 5W resistors, cheap inductors...and I'd been reading "audiophile" sites about I unsoldered one crossover and measured the inductors and wrote up a schematic.

Over the years I've been spending a little at a time to upgrade the crossovers and I can easily tell you that there is real truth in what I've been seeing about "audiophile" technology. I've replaced the most obvious capacitor, the electrolytic one in front of the tweeter, with a good set of film capacitors, the resistors with inexpensive Mills 5W types (only a few dollars each) and one of the woofer caps with an Obbligato oil type cap. I have experienced a definite improvement in my listening. One way I've described it is that one early music CD, an Alia Vox collection, has a few pieces with vocals. Before the new resistors and caps, I used to skip a good half of the CD believing I didn't like particular songs. What was occurring is that the cheap components were resulting in a mess where the voices were too close in frequency, producing a blurry sludge. Irritating. Upon replacing the tweeter cap etc., I was suddenly interested in the entire CD...!!

Most recently I've replaced the small inductors in the tweeter circuits with $20.00 Mundorf coils. There is again a positive difference, detail revealed, depth improved, and more. But most importantly, I've taken the advice of humblehifi and bypassed the tweeter capacitor with a Vishay MKP1837 10nF (0.01uF) metalized film cap, each. Things have become even more open and detailed without anything becoming overwhelming, etc. It may be a tired metaphor but it is as if a somewhat dirty window were cleaned a bit more, revealing a bit more...

The best part? These caps cost $1.00 each. Note that some of the top audiophile caps can cost hundreds of dollars, each. You do need to have a good cap in the circuit for this bypass to really work but even a good one plus this should be a great combination. I've heard counter-melodies and details I'd never before heard in just the few CDs I've played since making this mod. I'm pulling out CDs to listen for fun, to know them better, which is the mark of any worth-while upgrade to a music system.

More: Yes, capacitors etc. take time to "burn in". I have noted a change in sonic character as this occurs as I modify these speakers. Expect it to a degree, as well.

Vishay Roederstein / ERO MKP1837 - 0,01uF / 100VDC / ± 1%


The Vishay MKP 1837 Review and Modification

Please note that excepting the Vishay bypass capacitor treatment, the differences may be described as "subtle", in that they're not huge, "everyone can hear it" differences. BUT. I'm definitely getting more out of my listening experiences as related to the Alia Vox CD. A difference compelling enough to not only keep but to pursue in other directions.

Friday, April 10, 2015

Fixing the Infinity PS210 Subwoofer

Just got a PS210 at a thrift store for cheap; plugged it in and quickly learned why...Googled its name and number plus the word "problem" and there it is; the amp is completely sealed inside a plastic chamber so air doesn't shoot out the RCA jacks, etc. This causes the amp to very quickly overheat and shut off. Right now I've got it playing happily along by removing the amp from the back panel so the tiny heatsink can breathe a minute.

When I first powered it up I experienced the dreaded Standby bug, which is it turning off the instant signal drops below a certain level. This can become oscillation. Haven't had it since removing the power supply from the cabinet. Yes, it's just sitting up against the unit, ugly as hell, so that needs to be addressed...I'm wondering about 1" nylon spacers and longer screws, so it's still mounted to the rear of the unit, but is held out enough to breathe. Ugly, but convenient.

Improvements? Mounting the amp externally with a larger heatsink. Bigger power supply capacitors (Nichicon Super Through if possible). C6 and C8...3300uF 80V. They're tall but thin so fat ones won't mount to the PCB. I like to increase both the capacitance and voltage ratings when replacing caps such as these.

That heat sink is way too small. Might need to get something better and mount the transistors to it off the PCB, requiring a bit of wiring. (This is something which apparently effects the highly-regarded Nakamichi Stasis receivers...the heat sinks don't get to breathe.)

One thing I'm noting is that the crossover frequency pot is intermittent. Its cutoff moves up and down, perhaps in league with the switch which makes it full-range. I note that pushing it a touch past its maximum setting opens it a bit more, when it's "down".

I also note that the mode switches produce a huge LF pop. Very bad. Haven't checked if that's "normal". :p

This is a nice subwoofer although I'm not yet convinced that a smaller, lighter cone isn't better for punch and kick of music versus the sustained LF rumble expected by home theatre enthusiasts.

Monday, April 6, 2015

Cluster interview (Dieter Moebius, 1997)

To: "Analogue Heaven",
From: Mike Peake,
Subject: Cluster interview (Dieter Moebius)
Date: Sun, 12 Jan 97 21:07:43 -0000

Cluster Interview

July 18, 1996. The German duo Cluster, (Dieter Moebius and Joachim
Roedelius) just did their first tour of America, despite nearly
twenty-five years of creating unique and unpretentious electronic
music. I was lucky to have had the opportunity to interview one of
the members with a friend a week after the concert at Spaceland, in
Los Angeles.

Dieter Moebius (DM), Kevin Anderson (KA), and Mike Peake (MP)

MP- Are you surprised by the response you've gotten in America on
this tour?
DM- Oh, yes, I can tell you I'm surprised, it's going so well,
and it's not always so many people, but they are all very happy and
it's really just amazing, and the fellows enjoy it a lot.
KA- Because of the response to the current tour you are doing, are
you thinking of doing any future tours, or are you just taking it one
step at a time?
DM- We are not thinking about it at all, if it happens, it would be
beautiful. Next year we have a little tour for the German Cultural
Institute, and some records to finish, so we will see.
MP- What records are you working on?
DM- We are going to make a tour CD when we finish the tour, and then
we go back and I finish a solo record that I am working on, and I
just finished a record with Neumier and a member of Die Krupps, and
have to make some edits on some things, so we are busy this year, I
MP- Have you guys always been busy with Cluster and other music?
DM- More or less; Joachim spends his time in Vienna with his wife and
children, doing his music and being a father, and I am just travelling
around, as well as making music and doing other things, some German
film music, mostly now making music again, but it was different kinds
of living in the last ten years.
KA- One of the things I'm curious about is the framework that
Cluster operates in. Mike was telling me that there is a Cluster
album about every four years or so, and then in the meantime, the two
of you each do your own thing with solo projects and collaborations
with other artists. Is that intentional, do you guys say "we'll
get back together in four years and do another album, see you 'till
DM- No, it just happens like that, it's when somebody is in a good
mood and there's some time left over and it also happens by
accident, we both have the time to meet and work on something.
MP- What countries have you had the best response from, where have
you been the most welcome with your music?
DM- It was always the United States, where we sold the most records.
MP- Really?
DM- Yes. And also the United Kingdom, and Canada, but really mostly
America. Really not so much in Germany and Europe. Italy also, but in
Italy they make lots of cassettes, and they buy not so many records.
KA- This is sort of an ongoing debate that I've been having, the
merits of vinyl verus compact discs. I was wondering what you prefer
listening to music on?
DM- Ah, I mean, from the handling it's really very good with CDs.
(laughs.) I don't like the plastic boxes, I hate them. I like the
old vinyl covers, they are bigger and it's nicer to look at, but I
hate it that all my records are broken. So, from the quality of the
sound I must say I can get along with the CD.
MP- Likewise. I don't personally care for the size (of the cover
art) with CDs. Kevin, I should mention that Moebius has done the
covers of a lot of the Cluster records and his own work; they are
always marvelous to look at and I despise the fact that the CDs are
so small. It makes me want to order a large version of the complete
work. Speaking of Cluster projects, I heard a rumor at the concert
(at Spaceland club, LA) that between Curiosum and Apropos Cluster,
there were two Cluster records released in Spain, but not
internationally. Is this true?
DM- I don't think there was anything released in Spain that was not
exported to America. I don't know now what records you mean. There
was something of (GARBLED) that came out in Spain, there was
(GARBLED)sie Hausen (??) One Hour was also released in America, and
MP- Is there any particular reason Sky Records has taken so long to
release Grosses Wasser and Curiosum on CD?
DM- I think they had some problems, first he sold all his rights for
CDs I think to a company, then he got them back. As far as I know.
KA- I'm wondering, because of what Mike was asking about the
release in Spain, the thing that came to my mind was that perhaps
that was some type of bootleg, or counterfeit record. I was wondering
if you're aware if there is sort of an underground scene, people
trading Cluster records of concerts...
DM- (Quietly) Yes, I know. There are some bootlegs I know already
that are produced in Europe and Luxembourg; we can't do anything.
I'm not anywhere (powerful), I'm not police and I'm sad because
it makes me be not more rich than I am, and I'm not anyway.
(Laughter) I'm not happy, but I can't change it.
MP- What keyboards and pieces of gear have been your favorites to
use over the years?
DM- Of course I like my very new one, the Prophecy. It's my first
real digital one, and although I tend to like to work analog, this is
a digital that's working in a way like analog, a little bit, it's
fun. I also like my JX-3P, the Roland, it's half analog; and my ARP
Odyssey and Axxe. That's all I have.
MP- You've been very prolific with those. Do you remember what
keyboard you used for the bass sound on "Oh Odessa"?
DM- Oh no! That's not really an easy question, you can kill me and
I would not know it! On which record is it?
MP- Curiosum, the first track.
DM- Curiosum. It's perhaps an ARP, but I can't say, really.
KA- Pop quiz!! (laughter). Another sort of question that's a little
bit less technical is, when you're not busy in the studio, and
writing songs for Cluster and your solo work, do you listen to music,
and if so, what are some of the bands that you are listening to now?
DM- It's a very different kind of music I listen to, I listen to
all kinds of international music, coming from every place; when I
listen to American it's mostly things like Captain Beefheart or Tom
Waits. All kinds of music, you know. What I don't listen to is
electronic music!
KA- Do you have a personal favorite Cluster album, one that you're
just more proud of than the rest?
DM- Oh, mostly the last one, One Hour I liked, and the next that's
coming, of course! (laughter) And I liked Sowiesoso, and also
Zuckerzeit, I like them. I like them all in a way.
MP- What have your favorite collaborations been?
DM- I have to say it's Mr. Beerbohm, who's my best friend. He
lives in Berlin. It just works sometimes together because it's fun.
MP- Could you tell us a little about your creative process?
DM- Oh, this is really just always improvised, and coming from one
second to the next. We always work in a multitrack studio, of course
this is more than improvising; we build up, but we begin by
improvising anyway.
MP- You're not using any computer sequencing?
DM- No no, never, never, computer sequencing, we are to stupid to
even... We're really not into computer machines, we always need
somebody else to help us record. When we make a recording just on our
DATs like One Hour, we go to a studio to get somebody to put it
MP- With the computer, the tendency is to over edit and go back and
fine tune, until the life of the performance can be extinguished.
DM- Yeah.
MP- Improvising directly to tape, that's something Cluster fans
might be tempted to try themselves.
KA- My last question is if you have any plans, because of the
enthusiasm you've been greeted with, are you even contemplating the
idea of doing a live album?
DM- We are doing a live album now, we record every show, it's going
to be a double album, and we play together with this band Bond, and
The Brain, and it's a whole big show we make, we are really five
people, they play first and then we come, and we are going to make a
big bonus track on both CDs from both Bond and The Brain, so it's
going to be a really lovely live CD of us.
KA- Will this be on Sky Records?
DM- No, it's coming out in America on Gyroscope/Cleopatra. It's
going to be "Cluster Live in America, the Erste Begegnungen (First
Encounter) tour".
MP- Will Americans be able to find any of your film music work?
DM- No, it's just in Germany.
MP- The cities you chose on the tour were probably related to record
sales over the years; I'm interested why you didn't choose to
play Detroit. I was always able to find your records there, but since
I've been in LA, it's very, very difficult (Note: this should
change with Gyroscope's recent release of the entire Cluster
catalog on CD, available through Curious Music).
DM- We would have liked to, but it didn't happen.
KA- (Laughs.) That's a very diplomatic answer.
DM- Because Diane, our fantastic tour booking agent didn't make a
booking in Detroit, because she hates the cars. (Laughter)
KA- We thank you for your time!

Contact Curious Records for the complete Cluster catalog. Many
thanks to Russ Curry of Curious Music for arranging the interview,
for making Cluster's music available in the US, and for arranging
their tour.

Curious Music
1847 Clarice Court
Coralville, Iowa



Source of Uncertainty/Stack Collision with Heap/Condemned to Freedom

Wednesday, March 18, 2015

Buchla Quad Opto LPF DIY

Buchla 410 Quad Lopass Filter clone

This is the filter from the Buchla 410 Module Cluster found only in the CBS Performance III instrument. It is a slightly later version of the 192 dual opto LPF module, which some modified for CV in alongside the front panel Frequency pot. You might have to have an account on to see Buchlajoe's photo of a 192. Note the shrinkwrap for opto isolation; not sure if the distance provided alters the response characteristics.

Edit: It IS basically the same circuit as the Buchla 192 opto LPF which originally lacked CV inputs (the pot provided 0-15V). I've modded this 410 circuit into a 192 and they sound and act alike. The 192 loses the negative voltage rail. Thanks to the user who shared photos of a vintage module!

It uses +/-15V power rails and incandescent lamps and photoresistors. I dropped in 14V lamps and the only type of photoresistor at my local surplus dealer and it works perfectly.

As lamps are slower than the LEDs in vactrols, expect a much slower decay, especially if you're only used to the 5C3 vactrol!

On my build I find the filter closes completely at minimum CV input, cutting off bass lines and bass drums as I fed CDs into it. It doesn't quite open all the way to pass through the very highest frequencies; this may be due to the lamp and photoresistor combination I've used. Your experience may vary.

Quick soundbites:

Incandescent lamps and photoresistors.
Test build.



The 2N4339 is again available at mouser although they're a bit pricey. For this use, a J201 might suffice. There is a Vishay 2N4339-E3 but I haven't tried it out. It's less expensive than the InterFET version. J201 at mouser are $3.30, part #106-J201.

The original used the enormous Mallory PVC large film type capacitors found throughout the 100 series and in some 200 modules. It's thought that like the 910pF ceramic capacitors found in certain non-critical spots that Don had access to military and consumer surplus deals and used them applicably. The good news is that the Mallory PVC have become known as good-sounding. Modern "Orange Drop" capacitors are fully applicable for this circuit as well, although large pitch solder footprints have not been provided for them. Vishay MKP1837 and 1830 "ERO" film type box capacitors with a 5mm pitch are fully acceptable and they have a very good reputation for sonics in certain circles.

The 2N3565 may be swapped for 2N3904 or other generic NPN. The 4248 may be swapped for 2N3906 or other generic PNP.

The only electrolytic capacitor's value is a bit difficult to suss from the schematic; it looks like 100uF. 10uF might be fine in the same place; I don't know. I've used a 100uF audio grade Elna Silmic II in my recent perf build and it's fine.

Provision is given to include on the trace/solder side, a pair of "D" case 15uF tantalum capacitors for power smoothing. 


Buchla 410 Quad Filter Etch

Click here to download the PDF from which to etch.


Buchla 410 Quad LPF Parts

Note the single short bare wire jumper at the center of the PCB, as well as that being where the -15V supply is fed. You may optionally solder in "D" case 15uF tantalum SMD capacitors of the type used in Roman's builds for power supply smoothing.

Yes, I've taken my artwork from the 410 build and copied and flipped it around to create this layout, causing the text and parts legend to become reversed in places. I'm leaving it like this in the interest of saving the time it would take to do a cosmetic and applying it to module builds and the development of new module layouts. I'm pleased with the symmetry apparent in this layout.


Buchla 410 Quad Filter Continuity


Buchla 410 LPF Resistors

Buchla 410 LPF Build

Before worrying about isolating the lamps and photoresistors you'll want to do the standard pre-power check-over...looking for any solder bridges, cold solder joints, etc.


With no other connections besides power, the lamps should all be fully dark. A single reversed PNP transistor can cause most of them to slightly illuminate as well as not function properly. You of course need to confirm full functionality prior to sealing up the opto sections.

Using an alligator clip or probe which is connected to +15V, touch it to the input side of each 150K resistor (toward the input solder pad). Both lamps per quadrant should fully illuminate. 


Shrink wrap becomes opto shield/casing
You can take a 1/2" diameter piece of black shrink wrap to isolate the lamps and resistors, one tube per lamp + resistor and seal the open ends with epoxy or electrical tape.

The lamps and photoresistors may need to be directly in contact with each other. Checking this out...


I'm going to use interrupting audio jacks on the two right-side filters so that the audio output of the left filter normally runs into the second; this will result in a 24dB cutoff slope at the output of the second filter. Modulate both filters equally with the same source(s). To use the second filter independently simply plug in an audio jack.

The CV pots have +15V to the right side lug and ground on the left, with the center lug going to the Pot in solder pad at the 150K resistors at the outside corners of the PCB. The CV ins can be wired directly to the input banana jacks or you can put a 10K pot in this path, in to the right lug, left to ground, and center to the PCB CV input solder pad.

Note that I've supplied extra ground and +15V solder pads which are to be wired to the front panel as needed. Don't forget to wire a ground wire to one of the audio jack ground lugs. One is fine; you don't have to chain all of the audio jack grounds. The front panel acts as a ground plane to all audio jack grounds. This is how Don did it.


This module is from the Buchla era of 15V CV controller ranges. To use with 10V types (later 200 modules, 200r clones, and 200e systems) swap the 68K resistors at the CV IN solder pads for 47K or similar value resistors. Exact values have not been determined in use.

Adding resonance: Working upon a daughter board with opamps to provide resonance. Will be optional for purists wishing to avoid any and all opamps in their 100 clones.

Note that the 106 mixer cannot be used to add resonance to this circuit; the 106 sums both sections to the "ALL" output, and you need a single inverting section to be independent of that output. You can of course disconnect one of the sections from the ALL output by removing its 68K resistor to the ALL summing section, but there is not enough gain in the circuit to produce more than a very subtle increase in resonance.


The circuit appears to behave as do ladder filters when resonance is increased: the passband reduces in volume. This means not so much bass when you increase resonance...but with four filters, you can run two in parallel and sum them in a mixer, one with res and one without...

Friday, January 30, 2015

Buchla 106 Mixer DIY Version 2b

This is a new, confirmed/tested layout of the 106 discrete mixer. A previous version included an ill-fated attempt at adding inversion per channel. This version is per the original schematic only, and adds the convenience of PCB-mount potentiometers.

The main issue with this design is to make sure all of your transistors are matched for gain, all six in the same range, better than 5%.

2N3565 are specified for this circuit but 2N3904 are just fine. Elna Silmic II audio-grade capacitors are fine (100uF 35V, 10uF 50V). The 220r, 2K2, 1K, and 10K may all be carbon composition type resistors if you wish. 5% tolerance carbon film are fine for the rest of the circuit.

Alpha 9mm PCB-mount snap-in 50K audio taper pots are used (6 quantity), available from and THONK. Modifications are required prior to mounting and soldering them to the PCB; please see my 156 Dual CV Processor post for instructions and ordering. Note that three washers on each pot behind the front panel results in a perfect shaft height to support the Davies knobs slightly above the front panel without rubbing. Don't use a washer on the front side, just a nut each, to secure everything.


+15V and ground. 


Download by clicking here.


Buchla 106 V2b Continuity
Unsure what happened here; listen to 8-bit electro while viewing this image.


Buchla 106 Version 2b Final Parts

Note the single 68K which is mounted on the trace side of the PCB. The green line is a bare wire jumper.

Buchla 106 V2B solder/trace side

Buchla 106 detail
Detail of the trace-side mounted 68K resistor.

A .040" #60 drillbit is used for all Alpha pot holes.

Buchla 106 V2B parts side

All pots must be modified like this; procedure is detailed in my 156 post.


Here is the original schematic. You'll note some discrepancies between channels. There are swaps between 10uF and 100uF in places. Two versions have different pF range cap values.


The wiring pads are beneath their target audio jacks, for the most part.

Buchla 106 mixer V2 wiring
A sharp eye will catch that the left-side blue wire is connected to the ground lug and not the signal. I caught that during testing.


This will be a new, better-aligned artwork coming shortly. The old one will be slightly off.

Thursday, January 29, 2015

Buchla 175 Dual EQ / Line Driver DIY

Buchla 175 Equalizer Line Driver clone

Many thanks to the good gent who documented his vintage 175 module for this project. Oddly, I've had to change the circuit from what was shown on his actual module...have sent him this prototype for comparison; will comment if any differences are detected.

This is a discrete, dual equalizer module with bass cut/boost and treble cut/boost per channel (two channels). No opamps. Very useful for shaping the input or output of the 190 dual reverberation module or for general tone shaping. It is unknown why EQ is not a regular function in all modular synthesizers. It is extremely useful for tone shaping in addition to filters, etc.

It is also known as a line driver module as it has a strong output. It should be able to drive headphones (if you wish to use it for such I'd recommend adding a dual audio pot as a volume control at the output of the circuit and of course an appropriately-sized headphone jack). My earbuds show it to have the same output level as the square output on a 144 clone, or apparently unity gain. The 144 causes the 175 to clip a bit when adding full bass boost.

Although the layout is optimized to mount the potentiometers directly to the PCB, if is certainly possible to stack two of these PCBs with standoffs and hand-wire to front panel pots for a quad module, or to add this PCB/circuit to another module build requiring EQ.


+15V and ground. +12V would likely work.


The 100 series is optimized for 1V signals. 


4) 2N3565 or 2N3904
2) 2N4916 or possibly 2N3906
2) 2N3566 or possibly a BC550C with an Hfe of 500 or so

All of the above types are available at

4) 100uF 35V Elna Silmic II audio-grade capacitors
4) 10uF 50V Elna Silmic II audio-grade capacitors
1) 2200uF electrolytic capacitor, Mouser 

1) 47r
4) 2K2
2) 10K
6) 6K8
2) 68K
6) 330r
4) 15K
2) 100r
2) 3K3
2) 33K
12) 1K5

Thanks to Mike S. for getting the resistor BOM in shape!

Optional: The 100r, 10K, 2K2, and 47r can all be carbon composition type resistors if you wish. 

2) .0047uF 100V "Orange Drop" capacitors, Mouser
4) .22uF 100V "Orange Drop" capacitors, Mouser have these 400V (as seen in the pics).

These are the core capacitors for the EQ. The "Orange Drop" types are known for sounding good and are fairly easy to acquire; many tube amplifier and guitar parts shops have them. Know they are fairly large and you'll have to bend the leads to work with this PCB.

The original caps were precursors to the "Orange Drop" types, being Mallory polyester types often seen in the Buchla modules (huge, cabernet-colored types he must have gotten in quantity from his aerospace connections).

Pots are unknown; my prototype uses 250K linears. I've just completed the prototype pictured with 1M Audio taper and can confirm, =use linear taper=. 250K should be good. 1M is also just fine. I haven't tested to see if 1M provides any greater amount of control range.

A .040" #60 drillbit is used for the Alpha pot  stand off and lead holes.

Buchla 175 clone

Buchla 175 clone
In the event of a water landing, the Orange Drop capacitors double as flotation devices. 

Buchla 175 clone


Click here to download the PDF file.


175 V2 Continuity

Note that ground continuity only functions after the installation of the jumpers.


175 V2 Parts Legend

Note that the 3K3 with the asterisks (*) at the center are unknown; my second build, pictured here, did not use them so use them if you wish, or not.

Green lines are bare wire jumpers.


-Note that the input/output wires are shielded; ground them at the front panel jacks but trim the shield from the end soldered to the PCB.

-Pots are 1M linear taper Alpha 9mm snap-in PCB-mount types available from and THONK. Some modification is required; please see this post for specific instructions.

-Remember 1mm drillbits (#60) are perfect for the pot leads and standoff pins.

-Note that the potentiometer standoff pins may be soldered onto the PCB; provision is made in the ground areas for such and it causes the pot shaft to become ground.

-Put the finished PCB up to a bright light (behind the PCB) to check the potentiometer soldering for bridging.
-Do a continuity check before powering it up. Bridging may occur to ground while soldering.

All pots must be modified like this; procedure is detailed in my 156 post.


175 V2 Front panel art

Click here to download the correctly-sized PDF file.