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

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

cvgtMM - A ModuleModule version of the CVGT1

This project has kept me busy for the past few months. It was suggested some while ago that I do a ModuleModule version of CVGT1 to go in a Buchla (see my earlier post). My initial thoughts were that it was probably not the best solution as front panel space in a ModuleModule is quite restricted and Buchla real-estate is not cheap. However what I didn't consider was that Buchla can also talk to Serge, BugBrand, Fenix etc and Serge users seemed to want this solution. Consequently I set about designing (or redesigning) CVGT1 to fit in a ModuleModule form factor. Chris Muir from Eardrill produced a great interface document which defines just about all I needed to know for designing a ModuleModule (I'll refer to ModuleModule as MM from now on). 

Because of the smaller front panel space I had to lose some features i.e. scaling and offset on the Buchla to other synth CV channel but as it is in a Buchla and will interface to an external 1V/octave synth I've fixed the scaling at 0.8333 (1/1.2) and zero offset. The PCB design allows either 3.5mm jacks or 4mm bananas to be fitted; so one PCB can be configured to for Euro or Serge etc.

Clearly this design has PCBs parallel to the front panel unlike CVGT1 which has them perpendicular hence the change in jack style.  The PCBs had a completely new layout with all front panel related parts on the first board (Front Panel Interface Board) and most of the circuitry on the second (Main Board). Here are some design images of the variants (there are a few very minor tweeks to the graphic since this was drawn and you'll see a few variations in the prototype pics below).

I built a prototype and that's all working nicely. Aside from the new PCB layouts I had to make some changes to the pulse/trigger/gate circuits to run from ±15V rather than ±12V but there were no major changes. Heres a scope image of the Buchla compatible pulse I achieved:-

Here's the prototype with an ink jet printed plastic overlay on the front panel.

All components are conventional through-hole types - I may go over to surface mount if I get more orders than I can personally cope with but think I will still retain through-hole if anyone fancies a kit. You will also notice that the scaling trimmers are front-panel accessible (with a small screw driver) however these are for very fine trimming ±0.5%.

The first pre-production modules will be available in just over a week when the screen-printed panels are in stock. I have a number of interested 'customers' that I will contact soon and will start a pre-order list; please feel free to contact me to get on the list: It will be a 'no-commitment no money up front' arrangement as before with CVGT1 and I will poll all interested parties in turn when I have a module ready to ship to see if you want one. I have not finalised a price yet but guess it will be in the same ballpark as Eardrill's own range of single panel medium complexity MMs.

It will be interesting to see how this takes off, CVGT1 started slow and now there are 200 out there with bags of interest still.  I will do an update in the next week or so. Thanks for reading.

Another custom built Euro to Buchla Translator module

I was recently commissioned by a client to build a custom Euro Buchla interface module, similar to the two I previously built, but with offset switching. The previous two designs both had fixed offset and gain and were intended for use with envelopes, LFOs etc. In other words there was no 1V/octave to 1.2V/octave scaling required just offsetting to ensure the Euro signals stayed in the 0-10V range of the Buchla (you can refer back to my earlier post here).

This module is intended to be used alongside my client's CVGT1 module (which provides the ground reference connection) and adds more CV channels. My client uses Expert Sleepers' SilentWay software for pitch sensitive CV and was not interested in scale conversion as the software does the necessary recalibration however he also wanted the flexibility to be able to interface envelopes, transients and LFOs and so wanted to be able to DC shift signals when he needed to.

The spec was 4 channels of Euro to Buchla (scale of 1, 0V or +5V offset) and 1 channel of Buchla to Euro (scale of 1, 0V or -5V offset); so 10 connectors a 5 switches in 8HP.  

My 8HP prototyping panels proved to be difficult as the existing hole positions meant that the connectors and switches would have been too close to each other plus I only had a few left and found they were scratched; they got binned. I used Schaeffer for a quick-turnaround panel; not cheap but very well made. In a moment of madness I got 5 panels made, including engraving (which the original 2 modules didn't have).

Euro to Buchla CV Interface Module

I was commissioned by a client to design and build an interface module that allowed his Euro synth to modulate his Buchla synth and vice-versa.

Format Jumbler?

Euro uses 3.5mm mini jack sockets and Buchla uses 4mm banana sockets (which are colour coded). However this design is not just a 'format jumbler' because aside from the connector differences the signal ranges are different.  Buchla uses CV signals in the range of 0V to +10V and Euro uses nominally ±5V (well actually anywhere between -11ish Volts to +11ish Volts).  My client wanted 4 channels of Euro to Buchla and 1 channel of Buchla to Euro. 

Design Spec

The design spec I settled on was ±5V in (Euro) gives 0V to +10V out (Buchla) on channels 1 to 4 and 0V to +10V in (Buchla) gives ±5V out (Euro) on channel 5. As you can see the inputs and outputs both have 10V swings and so a gain of 1 is required but with a 5V offset (-5V one way and +5V the other). The input impedance of 100k and output impedance of 1k was used as it's fairly standard.  I used clamping diodes on the Buchla outputs so that an input more negative than -5V didn't cause a negative output to the Buchla. Because there might not be a common ground reference between the two synths a GND socket was also added to the design. Note that Buchla colour coding uses black for CV outputs and ground connections, blue for CV inputs.

Implementation

As the job was for just one module I used one of my standard 8HP front panels (order code 8HPP) and a new DIY prototyping PCB (order code DIY3) to build the design onto. 

The 8HPP front panel has 10 3mm pilot holes which had to be opened out to fit the 4mm and 3.5mm sockets plus a new hole for the GND socket. I settled on the position for the GND socket equidistant between the four lowest connectors really just for best spacing; I looked at putting it below the lowest two connectors but decided (incorrectly) that there would be not enough space to get fingers in and also avoid the mounting rail.

8HPJ (left) and 8HPP (right) Front Panels

The DIY3 is a bigger version of the DIY2 prototyping board and allows more complex circuitry to be realised due to the larger breadboarding area, power rail support for op-amps and A-100 Bus support (it is effectively a hybrid between DIY1 and DIY2 boards). The idea behind DIY3 was to be able to do more with jack-socket only designs such as buffered mults and attenuators, amplifiers, logic and gate/trigger circuits etc.

DIY3 Prototyping Board

The First Module

Here is the first module which I'm pleased with. It showcases the DIY prototyping board's capability nicely. The client was happy too.

The Second Module

On the back of the first order another client expressed an interest in the same functionality but preferred the GND socket to go below the lower two connectors. There was enough room to clear the mounting rail but pushes it closer to the channel 5 connectors than is ideal but still looks ok.

Further Modules?

I have another two expressions of interest for these modules especially if they were production rather than prototype versions. One suggestion was for front panel graphics to be added using the same font/style as Buchla which I like the idea of. Another thought is that not just CV translation is useful, gate/trigger translation would be useful too (as they are not compatible between the two 'standards'). I could also provide these as very basic kits (all the bits you need, a circuit diagram and a layout pattern). If I can get a few more interested parties to make it viable I would consider a small production run with purpose designed PCBs and a screen printed front panel. So if there is any interest out there please make your thoughts known to me.

Cheap DIY front panels from UK DIY store!!!

Tone's Top Tip for July

Whilst wandering around my local Homebase DIY store I noticed a rack of metal and plastic extrusions. In there was a range of 2mm thick aluminium clear anodised strip in 10mm, 15mm, 20mm, 25mm and 30mm widths i.e. approximately 2HP, 3HP, 4HP, 5HP and 6HP respectively (note that the online links wrongly refer to it as flat tube and not all widths are listed online). The strips are 1m long and cost between £4.50 and £8.00 each. They have a similar finish to Doepfer front panels but with a slight vertical graining. Here's a pic of 6HP and 4HP strips.

If you are OK at cutting and drilling they are a cheap solution to narrow DIY panels. Good dimension info here. I guess they are available in most large DIY stores so it's worth having a look next time you are there.

Eurorack synth prototyping products now available

Please check out the product and support pages on this blog. 

Kits and cables are also available through eBay; just search "Modular synth prototyping kit" or click here

Update on New Eurorack modular synth prototyping kits - Circuit boards have arrived

The new DIY prototyping circuit boards have arrived. They look good and the quality is very good.

The pots, pot brackets, headers, caps and jacks all fit which which is a huge relief.  To give you an idea of what they'll look like assembled checkout the preliminary piccies below of both types of board with some components assembled ready for prototyping to start. Note I have added some LEDS to one of the DIY2 boards too.

Time now to sort out the packaging, data pack, options and pricing - about another week before they become available.

Update on front panel artworks

Just thought I'd give a little more detail on front panel artworks as there is already some interest.

The picture below of my module currently in development shows the CAD drawing for a 12HP front panel in the top left. The adjacent front panel overlays show an evolution from a very simple, flat looking artwork to more 'sexy' metallic looking and coloured alternatives with some apparent depth.

 
Edit 08/07/11: The following graphics, based on ink-jet/laser printable vinyl overlays, was attempted on the first off batch of CV Tools modules but has been withdrawn in favour of a standard screen printed panel for two reasons. The first was that it was not liked that much by customers; people saw it as a cheap label. The second was that it was expensive and difficult to apply accurately. I will still use the overlays for prototypes.Please read the following but note it has all been superceded by events.

My task is to make this a service that is affordable by streamlining how I go about setting out the pot scaling, legends, functional grouping (separating lines or boxes). A good place to start from is if you use Schaeffer Front Panel Designer to get the panel made then I can use the DXF file generated to align the graphics to the holes; obviously with as much description from you as possible about what you actually want to see.

The one-off 2mm anodised panel from Schaeffer cost me 27 Euros (about 23GBP, $35US but it is beautifully machined!!); I anticipate the cost of an artworked plastic overlay would need to be less for that size panel to make it attractive, including my design effort (that's why I need to streamline the process - the slicker I get the more viable it'll be!).

The hardest part is lining up the overlay accurately on the panel as the overlay is self-adhesive. I'm getting quite adept at this now as I have prototyped several overlay types. You do get several chances and I may include a spare.

I am still developing the technology as it needs to have great graphics, be cheap to make whilst still having good wear and scratch resistance properties.  This balance is not easy and I will still need to explore better processes and techniques so initially this will be for smaller prototypes with some caviats on how much abuse it can handle. The artwork is great quality though and the durability is reasonable but could be better. The price will reflect this fact. Having said all that I'm going to use it in my system as it stands as I don't tend to abuse my hardware.

Any suggestions and comments would be most welcome.

New Eurorack modular synth prototyping kits preview

Hello fellow synth fans,

In the next few weeks I will be producing a range of Eurorack standard modular synth prototyping kits for synth constructors and enthusiasts; these kits will comprise Doepfer compatible printed circuit boards (PCBs) and components. 

These  will enable you to make neat prototype or one-off projects that accomodate bracketed pots, PCB mounted jacks, switches and LEDS so that they can be easily mounted to a module front panel.

The idea is that you build your designs on the breadboards supplied and get the front panel manufactured separately, either by yourself, or by a company such as Schaeffer http://www.schaeffer-ag.de/en (I can provide some template files that you can use directly or can modify as you require. I will also look at providing some standard panels e.g. five pots and five jacks but this is still being costed; more on this in the coming weeks).

I will also be able to provide you with a relatively low cost high quality front panel overlay to give your module a professional appearance; this service will also be explained in more depth in the coming weeks.

This is an overlay I made for a product in development
(this is the next product - a versatile voltage processor)

There will be 3 kits available:


Kit 1: This comprises 2 single-sided prototyping matrix-type breadboards and cable as follows:-

• DIY1. This PCB is primarily for mounting control pots and prototyping most of the circuitry on a breadboarding area.  It is provided with 5 control pots and mounting brackets; the pot values supplied are 50k linear (type B) but you can request 10k, 100k linears (type B) or 1M log (type A); 2 100nF decoupling capacitors and a 16-pin header are supplied fitted to the board; the pots and brackets are supplied loose. Not all pots need to be fitted and there is provision for PCB mounting of LEDS. The PCB has +12V, -12V and 0V busses.

• DIY2. This PCB is primarily for mounting jack sockets but switches (Taiway series 200 sub-min toggle switches) and LEDS can also be fitted.  It has a smaller breadboarding area than DIY 1. It is provided with 5  3.5mm jack sockets but some can be left out to fit switches or LEDs.

• Doepfer compatible ribbon cable.

• Data sheet.

Kit 2: This comprises just the DIY 1 breadboard and five pots and brackets.


Kit 3: This comprises just the DIY 2 breadboard and five jack sockets.

A range of components such as pots, brackets, knobs, jacks and cables will also be available.

This is just a preview and I will put up more details, costs and photos in the coming weeks.