Custom Half-width Buchla Modules

I was asked to design and build a pair of custom half-width Buchla modules for some clients. They each had two half-width slots spare in their custom built cases and wanted to fill the spaces with Euro to Buchla CV and gate translator modules.


The brief was simple (and the same for both clients): 5 channels of 1V/oct to 1.2V/oct CV translation and 5 channels of gate boosting to Buchla levels; the Buchla stepped pulse was not required, just big pulses (10V or more).

This was a great opportunity to use the Synovatron Proto range of prototyping boards which accomodate 5 channels and offer stackability if more circuitry is required than will fit on one board; see below.

The Proto range of boards

As the Proto boards are designed primarily for Euro there was space on the 4U Buchla front panels to add some extras in the form of a passive attenuator. Here are the front panel designs that we agreed on:-

CV and Gate modules

To keep costs down it was decided not to have panel marking as the functions are obvious.

The CV module design used a straightforward precision amplifier with gain of 1.2000 (yes that accurate), 1M Ohm input and 0 Ohm output impedances. The gate module used comparators and output and LED drivers. The outputs each have diodes in series allowing them to be wire-ORed by just connecting outputs together (common to Buchla, wish it was used on Euro).

The CV module electronics fitted nicely on a ProtoJax board with plenty of space as you can see:-

For the gate module I decided to put the input comparators and sockets on the ProtoJax board and output buffers and LEDs on the ProtoXp board and stack them together (it  probably could all have been put on one board but it was simpler to make use of the space). The stacked ProtoJax and ProtoXp boards can be seen here:-

The gate board was powered from an MTA connector and the CV board took its power from the gate module (hence the 10-pin ribbon headers for a linking ribbon cable); this was at the client's request as they only had one spare connector (these are very low current modules and daisy chaining them didn't cause any crosstalk issues). 

The finished panels looked pretty good; they were made by Schaeffer using Front Panel Designer http://www.schaeffer-ag.de/en/front_panel_designer/the_idea/.

  
If you are interested in the Proto range of PCBs or in having a custom module built then please contact me at synovatron@btinternet.com

Synth Repairs

Analogue Systems RS-40 Noise, Sample and Hold, Osc

This came in as 'defective'. After a while it became obvious the noise output was not working. This was traced to an open-circuit LEVEL contol pot (10k lin) which was replaced. Still it didn't work as a sample and hold - i.e. I was expecting to see a stepped output from S\H OUT. Not having used the RS-40 before it took me a while to realise that the noise and clock signals are not normalled to the Sample and Hold circuit like the front panel markings suggest; the lines linking NOISE OUT to EXT SRC IN and INT CK OUT to EXT CK IN suggest to me these are linked in some way but no. 

RS-40

After looking at the jacks it was clear that these are not normalled (I'm not sure if this is the case with all RS-40s but this one looked clean and unmodified so I'm assuming it was factory standard). I used external patch leads and to link the noise and clock outs and ins and hey presto it worked. The first thing that I saw on the scope was at each sample point the sampled signal is present for what I guess is the duration of the sample pulse (about 0.2ms). When using the RS-40 to modulate a VCO I could not tell that the noise spikes were a problem, in fact it is probably above hearing range (at least mine). 
 

Noise spikes

However I didn't much like it and I didn't much like not having the noise and clock not normalled to the S/H circuit. I spoke to the owner and he agreed to have a couple of simple mods applied.

The noise and clock signals are present on the jack board close to where they would have to go for normalled connections. The switched contacts were connected to ground on both EXT SRC IN and EXT CK IN jacks by solder bridges. I removed the solder bridges and fitted links as can be seen here. This worked a treat allowing it to work without patching but still allowing external signals to be patched in if need be.

Solder removed from red arrows and links applied at yellow arrows

The noise spikes 'problem' although not audible was fixed by placing a 10nF cap across the S/H output amplifier's feedback resistor (27k) making it a low-pass filter with a cutoff of 590Hz. This got rid of the spikes without adding noticeable slew.

10nF capacitor

Spike free steps

5 into 1 Analogue Systems to Doepfer Bus Adaptor/Expander

The new 5ASM2DB Analogue Systems Module to Doepfer A-100 Bus Adaptor/Expander is now in stock and available to order. 

SchneidersLaden have stock of 5ASM2DB which can be ordered from their website at http://www.schneidersladen.de/en/manufacturer/synovatron.html.

For DIY enthusiasts it is also available as a kit or as a bare PCB direct from Synovatron (please email synovatron@btinternet.com). 

The 5ASM2DB offers five Analogue Systems sockets on one small circuit board with low-current LED indicators to show that ±12V and +5V power is available. It comes with a ribbon cable to connect to the A-100 bus and four self-adhesive nylon PCB mounting pillars (you can of course use screwed in pillars so a drilling template will be provided).

If you have several Analogue Systems modules in a Euro rack then the 5ASM2DB could be a better alternative to using several ASM2DB Adaptors because it expands the bus and frees up A-100 Bus connectors for Euro modules; it costs roughly the same as three ASM2DB Adaptors. ASM2DB and DM2ASB Adaptors are still available.

5ASM2DB Adaptor/Expander

5ASM2DB Adaptor/Expander

5ASM2DB DIY Kit

New product preview

This is a design that has been hanging around for over a year in a 95% complete state but I have now taken the bold step of finishing it and going into production. It is called the 5ASM2DB and is a 5 socket version of the popular ASM2DB Analogue Systems module to Doepfer bus Adaptor. It is fabricated on a small circuit board and has 3 LEDs that indicate the presence of ±12V and +5V. The 5ASM2DB will be supplied with 4 self-adhesive nylon mounting pillars and a short ribbon cable so it can be placed adjacent to a busboard and linked via the ribbon cable (standard Euro rack 16 pin cable). It is not recommended for use with the Analogue Systems RS-370 as this draws a whoppng 680mA from the 5V rail.

It will be priced at roughly that of 3 ASM2DB Adaptors so the aim is you get 5 for the price of 3; which will be of interest to those of you with many Analogue Systems modules to go in a Eurorack case.

Availability is from mid-September and will also be available as a DIY kit and as a bare PCB for the more adventurous DIYers. Here's an image from the CAD package - it will not be red BTW!

Confused by Cwejman ribbon cables?

I received an order to build some Cwejman standard ribbon cables that were 40cm long. Up until then I had no idea they were different to standard Eurorack cables. So here is what I found out and hopefully this takes the mystery out of it for anyone who is lucky enough to own one of these top modules (and it's also a sales plug - no pun intended).

Eurorack DIY Prototyping Cards Rethink

Post updated 3rd July 2018

The Synovatron Eurorack DIY Kits have now been discontinued. Because many of the kit components are easily available from online retailers it made sense that Synovatron just provides the unique (e.g. PCBs) and harder to source parts (e.g. pot brackets). This provided a great opportunity to reassess the PCB designs rather than just reorder more of the same.

What has emerged is a revised and rebranded Eurorack prototyping solution that is more usable and more elegant than before. The revised product revolves around three PCBs in the Synovatron Proto series: ProtoPotz, ProtoJax and ProtoXp. 

The new Proto PCBs' holes line up with each other to allow each board to be stacked one on the other using header plugs and sockets; allowing power and signals to be routed between boards without resorting to linking ribbon cables. Here is an example board stack-up:

ProtoJax, ProtoPotz and ProtoXp boards stacked together

Examples of headers and sockets used to stack the boards

ProtoPotz

ProtoPotz is the direct replacement for DIY1 PCB (as used in DIY Kit 1 and DIY Kit 2). It is designed to hold up to five 16mm P160KN series pots using brackets. What's new about it?

• Plated-through holes for robustness and convenience, essentially it's a double-sided PCB. 
• Better supports the A-100 bus with dedicated positions for 10 or 16-way open or boxed headers, small electrolytic capacitors and protection diodes (to protect against reverse power connection.

ProtoPotz pot breadboard PCB

Here is the range of pots available from Mouser that Synovatron recommends for use with ProtoPotz:-

ProtoJax

ProtoJax is an evolution of DIY2 and DIY3 PCBs. It is designed to hold up to five Cliff CL1384 3.5mm mono jacks. It is almost identical to ProtoPotz except it has footprints for jacks instead of pots and another two rows of breadboard holes. What makes it more advanced than DIY2 and DIY3 pcbs?

• Larger breadboarding area. 
• Supports the A-100 bus similar to ProtoPotz.

ProtoJax jack breadboard PCB

ProtoXp

ProtoXp is a completely new PCB. It is an eXpansion board designed to add more breadboarding area to ProtoPotz or ProtoJax boards. It's features are:-

• It has a cutout that allows the A-100 bus ribbon cable connector to fit without fouling on the ProtoXp board. 
• The same ±12V power bus structure as the ProtoPotz or ProtoJax boards.

ProtoXp expansion breadboard PCB

DIY2 jack breadboard PCB

 

DIY3 jack breadboard PCB

cvgt MM Buchla Translator ModuleModules

The first cvgt MM modules have started shipping to clients at the top of the pre-order list. If you want to be added to the list then please make contact on synovatron@btinternet.com

I will build in small batches and work through the list in chronological order and will then contact you when your order is ready to ship. Only at that point will I request payment (see prices below). Please note that this does not form any contract between us and you are not in any way commiting yourself to making a purchase until such a time that you make a payment.

 

Initially the cvgt MM will be only available directly from me but if there is enough demand then it is possible they will become available at all the usual distributors in due course. 

The current variants are:-

• Buchla-Euro (round or hex nuts on 3.5mm jacks; please select)
• Buchla-Serge*
• Buchla-BugBrand*
• Buchla-Fenix*

*These are banana socketed variants and only the colour of the banana sockets is different (to match the target system); All are variants (inc. Euro) are to translate from Buchla to 1V/octave systems.

The User Manual is being worked on and will be ready very soon and will posted here in an update. Please checkout the Eardrill website for more info on the ModuleModule concept and other great products from Chris Muir.

Euro variant

Serge variant

Euro (top), Serge (bottom)