Some Notes on Making Buchla-Compatible Stuff

This set of notes started life as a jumbled text file for my own use, mostly
consisting of copied & pasted bits of advice I received from the SDIY
mailing list. I thought others might find some of this info useful as well,
so I cleaned it up a bit and posted it here.

I plan to pick up a Buchla 200e system as some point, so I am interested in
some of my SDIY stuff being Buchla-compatible and having a similar overall
look and feel.
(Note, however, that I am not planning on selling front panels; they
are for my own personal use. I’m just planning on selling circuit boards,
so people can make panels in whatever their own favored format is.
The info here is available in case someone is
interested in doing similar things on their own.)

So-called 1/8″ jacks

It turns out this is a fairly complicated issue, since there doesn’t
really seem to be a 1/8″ jack. 3.5 mm jacks are common on modern equipment;
this correspond to 0.138 inches. (Going the other direction, 1/8″ corresponds
to 3.175 mm).

The so-called 1/8″ jacks used by Buchla are actually Tini-Jax, which are
0.141″. Chris Muir wrote: “My theory is that because the Tini-Jax were about
half the size of 1/4″ with the same general look,
they were just called 1/8″. I’ve seen no evidence that
Switchcraft ever called them 1/8″.
Plus… no one likes to say (or spell) Tini-Jax.”

0.141″ corresponds to 3.58 mm, which means they’re a bit too
big to fit in a 3.5 mm jack. They can sometimes be forced, I’m told, but
doing this will weaken or damage the jack. Conversely, some people have
successfully used 3.5 mm jacks in 0.141″ inch sockets, although others
recommend against trying that. “Flight” of wrote:

I’ve been looking into the whole 3.5mm vs. Switchcraft 0.141″, even talked
Switchraft into putting a 3.5mm bushing on their 142A to see if it would
work. In summation: NO. There is just enough difference to cause all kinds
of problems. I know that many have used them reliably as 3.5mm jacks, but
even Switchcraft says they are not a suitable jack for 3.5mm situations.

3.5mm plug –> 0.141″ jack: With the 142a, the plug is too narrow to operate
the NC switch, so it won’t disengage. The plug also sits at a bit of an
angle unless it can be seated against the bushing shoulder.

0.141″ PLUG –> 3.5mm jack: It takes a little more effort to get the plug
in, but it will go in and work fine (usually), but it also overstresses the
bends in the contact spring and 1) may permanently bend the spring, making
the jack useless for 3.5mm plugs; 2) *will* shorten the life of the jack –
they are not intended for plugs of that size.

Later, “flightofharmony” wrote:
“I just checked a number of different plugs that I have with a micrometer.
The 3.5mm plugs measure (nominally, +/- .02mm variation) 3.5mm at the
sleeve, 3.0mm at the tip. The 0.141″ plugs measure (same variance) 3.59mm at
the sleeve, 3.48mm at the tip. It is the 0.5mm tip difference that causes
the problems with the 142A.”

As far as Tini-Jax sockets goes, it seems
Mark Verbos has been happy with Switchcraft 41, noting that Buchla has been
using them since 1963. The 41 doesn’t have a normalled connection, but the
42A does. These both are panel mount with solder lugs.

Cary Roberts recommends against the 142A, noting that its normalled connection
on ARP equipment was failure prone (hence ARP later switched to using
panel-mounted 42As.)

is the datasheet for the Switchcraft 41, 42A, 142A and
The datasheet says they need 0.25″ mounting holes; conventional
wisdom indicates this is a good size for 3.5 mm jacks as well. (As an aside,
“megaohm” noted that Blacet uses Kobiconn 3.5 mm mono jacks, Mouser part
number 16P012, and that Blacet also sells 3.5 mm patchcords at a decent price.)

The Switchcraft Tini-Jax
jacks are
on p. 1130
of the Mouser catalog. The 41 and 42A have Mouser part numbers 502-41
($1.85 unit, $1.68 >10, $1.60 >25, $1.46 >$50) and
502-42A ($2.51 unit, $2.09 >10, $1.95 >25, 1.78 >50).

Chris Muir says the Mogami 3.5 mm cables from Analog Haven work OK in
0.141″ jacks.

Cynthia Webster sent me an e-mail recommending Switchcraft 142AX. She writes:
“The X at the end means the newer lead free version. These are not listed
as ‘switching’ jacks… They are instead ~Shunting~ jacks – so we do not
use them for switching functions,
And make them bulletproof reliable by shorting the
North & South pins together, and separately short the
East & West pins together. Works like a champ!”

Banana jacks

Buchla (at least modern ones) seem to use this convention:

  • CV inputs black, outputs blue (or sometimes if there’s multiple similar CV)
    in/out structures they will alternate inputs black, outputs blue with
    inputs gray, outputs

  • CV velocity green
  • pulse inputs orange
  • pulse outputs red

Cynthia Webster confirmed that Cyndustries uses Emerson/Johnson banana jacks,
and believe that Modcan uses them as well.
Chris Muir
thinks that Buchla and Serge (i.e. ST) currently use them as well. Oren
Leavitt also vouched for Emerson/Johnson. Ian Fritz has been using them since
Pomona no longer makes jacks in that style. “Megaohm” also recommends them
as being easy to solder and reasonably priced.








Green (typo in Mouser catalog erroneously says these are White)





You can create the Mouser part number
by putting “530” in the front.
They are on Mouser
catalog page 1148.
has these for $0.50 to $0.53 for singles, $0.41 to $0.46 for >10, and
$0.33 to $0.39 in batches of 100. Digikey has them for a few cents more, and
Newark has them for a few cents more than that.

Pomona is an alternative to the Emerson/Johnson jacks. Chris Muir noted
that the Pomona quality is probability better, but they are more expensive and
deeper. Anthony Bisset wrote: “I find patching with pomona to be just a
bit on the stiff side and favor the EF Johnson jacks as they can
actually break in.
No chance with the Pomona monoblock machined approach.”

For banana patch cords, “megaohm” recommends Pomona’s “stacking standard
banana plug
each end,” from
catalog p. 2121.
The Mouser part number is 565-BX-Y, where X is the
length in inches (4, 8, 12, 18, 24, 36,48, or 72) and Y is the color (0 for
black or 2 for red.) For larger quantities, “megaohm” recommends calling
Cyndustries, who sell “a variety of assorted lengths and colors in package


The text in this section was kindly provided by Chris Muir.

The round momentary switch that is
all over the 200e is the C&K D6R.
Mouser doesn’t carry this one, but
Digikey stocks it.

Note that it comes in two versions with differing amounts of
force required to activate it. I think Buchla and Associates has
used both forces, but newer modules seem to be the F2 model.


The conventional wisdom is that a 1/4″ mounting hole is good for most switches
that show up in SDIY.

Jason Butcher informed me that classic Buchla stuff used C&K switches such
as the 7211, 7101 and 7103. These seem to be hard to find and pricey when
they are findable.

Paul Schreiber recommended some
(manufacturer part
number M2012ES1W01 and similar numbers), which to my eyes to be
quite similar to the C&K switches. The NKK switches have an actuator length of

The cheapest I’ve found these is at Mouser
p. 1635

633-M201101-RO – SPST On-None-Off ($3.19 unit, $2.94 >25, $2.56 >50)
633-M201201-RO – SPDT On-None-On ($3.50 unit, $2.50 >25, $2.39 >50)
633-M201301-RO – SPDT On-Off-On ($4.10 unit, $2.98 >25, $2.70 >50)
633-M201501-RO – SPDT On-None-(On) (parens indicate momentary switch,
for instance, in the Music Easel’s Pulser)
($4.60 unit, $3.56 25, $3.25 50)
633-M202401-RO – SP3T On-On-On ($9.88 unit, $8.88 >25, $7.90 >50)

Still expensive, but Paul says their reliability is top notch. (Huh – for
reasons I don’t understand, the 25 and 50 prices of the On-None-Off switch
are higher than the On-None-On switch. You could just get the On-None-On and
not hook one side to anything… strange.)


I plan to use Alpha pots with 0.236″ (i.e. 6 mm) D-shafts.

If I spend money on Buchla gear, I’m going to be spending it on a 200e,
not on vintage gear. So I’m personally interested in matching the 200e
style, not the old 200 series styles.

Chris Muir reports that
has a $50 minimum order policy, and that
their online RFQ form goes into a black hole. He and Mark Verbos
recommend calling them. Chris says the following Selco part numbers will
give a 200e-ish look:

DRD 150 006
Large Skirt 15 mm
DCN 150 006
Medium 15 mm
DRN 110 006
Small Knob 11 mm
C151 Gray 6
lined grey cap for 15 mm medium and large
C111 Gray 6
lined grey cap for small 11 mm


Luther said the sliders on his Music Easel have the dimensions of: 57mm
(2.2″) length of slot, 43mm actual travel of slider, and 65mm between mounting
posts. Mark Verbos said that they were made by CTS but are out of production,
and that the same sliders were used in the ARP Odyssey, Axxe, Avator, and
Sequencer, and that someone is selling replacements on ebay that have
shorter shafts but work fine.

If one was making something new – i.e. not too worried about an exact match
to fit in an original slider, then the 1/4 watt linear Alpha slider
with Mouser number 312-9201F-Value (assuming you were OK with a linear slider),
where value is the max resistance (1K 5K 10K 20K 100K 500K, or 1M),
from p. 679,
of the Mouser catalog might work.
It has a claimed lever travel of 45mm and a post-to-post distance of 65mm,
and the total body length is 73 mm. The body width is 12.5 mm. From measuring
an actual slider, I recommend using a 58 mm by 3 mm square hole in the
front panel. ($1.35 for 1,
$1.08 for >10, $0.98 for >100). More detailed dimensions are on the
The catalog doesn’t list 50K, although
when I put 50K into the Mouser search engine it came up without any problem.
Sadly, Mouser doesn’t seem to have any logarithmic sliders (good for mixers,
etc.) in the same size. It does have a smaller logarithmic one, though.

The Music Easel assembly guide reports that the sliders in the Easel
are 50K audio taper, and the schematic itself says “50K.” For many
reasons, I am convinced
that this is in error, and that the sliders are actually 10K linear.

Buchla power connector standard

The text in this section was kindly provided by Chris Muir.

Power on a Buchla module is delivered from a dangling connector.
There is a somewhere between a foot and a foot and a half of wire
dangling from a module (strain relieved, of course) that terminates in
an edac 306-010-500-102 connector.

1 Black: quiet ground
2 White: -15
3 Red: +15
4 Dark Green: +12
5 Orange: +5
6 Brown: noisy ground
7 polarizing key
8 Yellow: i2c clock
9 Green: i2c data
10 nc

Mouser link for the power connector.

This connector plugs into edge fingers on a power distribution board.

Random wisdom

When planning hole sizes for front panels,
Mark Verbos recommends using a drill gauge like
this to make
sure parts really fit.

If you need to know about the “Metric Fine” system (i.e. you see something
using an M-number indication), see
here and
here (thanks to Graham
Atkins and Danjel van Tijn for the links).

Cynthia Webster’s advice on hole sizes for front panels made using panel
making services like Front Panel Express: “You can always
err on the side of ‘too small’ and easily enlarge the hole that they locate
and create by using a hand drill if necessary (better than making the hole
too large!)”

David Dixon’s recommended front panel hole sizes: 1/4″ for toggle switches,
5/16″ for Alpha pots, and 3/8″ for 1/4″ (e.g. MOTM style) jacks.

On a couple of my prototype boards, I got the input pins on op amps switched.
To get the prototype working, Ian Fritz suggested bending the offending pins
upward, and using wire wrap to connect to them and do the swap. Dr. Mabuse
recommend the following wire wrap dispenser tools from Mouser
p. 2133

801-WD-30-B Dispenser with 50′ of Blue wire $18.68
801-WD-30-Y Dispenser with 50′ of Yellow wire $18.68
801-WD-30-W Dispenser with 50′ of White wire $18.68
801-WD-30-R Dispenser with 50′ of Red wire $18.68
801-WD-30-TRI Dispenser with 50′ three colors $30.71

Frac rack notes

The notes below are primarily for my own use – I’m building my PCBs into
a frac rack format, but using Buchla connector conventions for the front
panel. I’m calling it the “frachla” format. 🙂

Frac rack modules are 5.25″ high, with widths in multiples of 1.5″. Per
instructions on the Blacet website, mounting holes are 1/8″ wide,
0.75″ inches from the left and right sides and 0.3″ from the top and bottom.
The top 1/2″ and bottom 1/2″ should be left clear to accommodate the mounting

PAiA style L-brackets for mounting PCBs to panels:
Mouser part number 534-612 (one hole threaded)
or 534-621 (both threaded, 4/40),
p. 1853

(thanks to “numbertalk” on electro-music).

#4-40 1/4″ machine screws, Mouser part number 5721-440-1/4SS ($4.80 for a
pack of 100), matching hex nuts 5721-440-SS ($4.99 for a pack of 100)
p. 2300

My PCB adaptations
all have a longest dimension of 100 mm (3.95″). The mounting holes
along this dimension are 3.75 inches apart.


No guarantees or warranties
are made about the correctness or usefulness of the information on these

Any electronic project may present a risk of injury or
death, particularly when
dealing with mains voltages. It is important to follow appropriate safety
practices. The author of these
pages, Aaron Lanterman,
disclaims any liability for injury, death, or other damage caused in
using the information contained on these webpages.

Aaron Lanterman, last updated 6/13/09