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Modular Synthesizer

Purchasing    Patch cables    Sequencing    DIY mods

Apr-2013 - Latest addition to the studio is a customised Studio-22 modular synthesizer from (aka dotcom), so this section documents progress & mods... with a few warnings for newbies like me! More info on modular synths can be found in this forum.

Studio22 system

One advantage over conventional synths is that the oscillators (and noise sources) are permanently running. I'd not fully appreciated this before, but it means you don't need any external gear to get sounds out of it. With previous synths & sound modules, you usually end up repeatedly pressing keys on a keyboard (or running a sequencer) while you tweak the knobs, but with the modular the sounds are there all the time - in fact you have to go out of your way to shut them up!

Note there's no output level control on these oscillators so don't plug a PA or headphones directly into them unless you have some external control over the volume. You can patch them via a module with a gain control such as an amplifier or mixer module, but either way watch those levels; 10v peak-to-peak signals can do a lot of damage!

So if you want instant drones, patch one or more oscillators to the amp, and try different pitches and waveforms. If you want a regular pulse to check out the envelope generators & filters, switch the sample & hold module to 'internal'; its gate input socket becomes a pulse output whose speed is controlled by the sample rate knob. There's endless possibilities even without connecting an external keyboard or sequencer.

This basic test video shows my first lash-up after switch-on.

Purchasing supply individual modules, cabinets and accessories as well as a range of complete plug & play 'studio' systems. The standard Studio-22 comprises a walnut cabinet pre-filled with a selection of 18 modules, blanking plates, an internal PSU and a set of 1/4" jack-to-jack patch cables, but you can customise the package contents as required. Either ask for price quotes via email or use their downloadable SynthInvent tool to design your own system with immediate feedback on cost.

SynthInvent screenshot

Module widths are measured in multiples of 'Moog units' or MU, e.g. the Q108 VCA module is 1 unit wide, the Q106 VCO is 2 units wide. The Studio-22 cabinet, as its name suggests, has space for 22 units at the front and 4 at the back.

The 18 default modules are mounted with 17 at the front, leaving one unit free, and one at the back, leaving 3 units free.

You can free up one more unit at the front by moving the Q101 power on/off module to the back, but you'll need access to the switch unless you use an external mains on/off switch.

You can reduce costs by replacing the Q101 & Q102 power modules with the combined Q137 module (mounted either at the front or the back), the trade-off being less power sockets for chaining to other units.

Costs can also be reduced by choosing the MDF cabinet, or leaving it out altogether if you can source your own. Ditto for the patch cables, but I found reducing the no. of shipping boxes had very little affect on the USA to UK postage costs.

My final choice was to use the Q137 as described above and mounted at the back, freeing up enough space at the front to add the 2-unit wide Q150 'Moog-like' ladder filter. I excluded the patch cables as I wanted to make my own, and this saving helped to justify the walnut cabinet. The latter took a lot of conscience-wrestling but it really is the icing on the cake! Including a cabinet also meant the whole system came ready-assembled & tested so it was just a case of 'plug in and play'.

N.B. the mains voltage selector switch had been left in the 110v position so check this before plugging in!

Modules from other vendors can be mixed with dotcom modules, but see forums for advice on power connections/adapters and physical dimensions.


Patch cables

Saving money by making your own can be a good idea... a few lengths of unbalanced screened cable, a handful of 1/4" mono jack plugs, a soldering iron... but be warned - not all cables are the same! 

Some cables marketed as 'instrument' cables have a conductive coating around the inner core for draining away static electricity to reduce crackles when the cable is flexed, e.g. for guitarists moving on stage. This conductivity has no effect on normal audio signals but if used for control voltages (CV), the resistance may cause the voltage to drop slightly, although this depends on how well the CV driver can cope with loading. If the voltage is being used to control pitch, this could throw the synth out of tune.

Coincidentally, the Q104 MIDI-to-CV module had a fault (subsequently fixed free of charge) which made it very susceptible to loading, so these anti-static instrument cables were no use initially. A fully working Q104 can drive many loads without voltage sag so instrument cable may have been ok, but either way I ended up replacing the patch leads with standard twin-core microphone cable with one core unused.

Colour coding
The pre-formed cables from are colour coded according to length, but a functional colour scheme may be more useful for following the flow of a patch. There doesn't seem to be a standard for this, so I copied one of the other synth vendors and used black for audio, red for control, blue for gates and yellow for anything else such as triggers etc. 

On the other hand, you could just leave them all the same colour as one of the advantages with voltage control is that control & audio voltages can be interchanged; e.g. you can control the pitch of one oscillator with the audio output of another, or even itself; so the function of a patch cable may be ambiguous anyway.


Sep-2013 - If you're after those nostalgic sequenced patterns of Tangerine Dream, Kraftwerk, Jean Michel Jarre etc. be warned - these synths are essentially monophonic, so creating lots of overlapping sequences in a live environment comes at a price.  There's no problem if you overdub layers during recording, but for live perfomances you may need more modules or additional synths.

A typical 'voice' in a subtractive synth like this uses a VCO as a note pitch source, and a triggered or gated VCF/EG/VCA combination to control its envelope, so the no. of concurrent voices depends on the no. of sources and whether or not you want independent triggering for each one. This customised Studio-22 system has 3 VCOs and 2 VCF/EG/VCA sets, so this limits you to 2 independent voices. There are various compromises & work-rounds such as mixing all 3 VCOs into a single EG/VCA giving 3 independent pitches but with a shared trigger, etc. Modules can also be used in non-conventional ways to emulate other modules, e.g. a VCF in self-resonating mode can act as a VCO; see forums for other ideas.

This video shows a simple 2-voice example using Sequetron to sequence multiple patterns live via MIDI. The supporting PC only has MIDI interfaces so these need converting to the various CVs (e.g. pitch, gate, trigger, velocity) to drive the synth; one converter is required for each voice.
I only had a single channel Q104, and there was no room for another module so an external device from Kenton was used for the 2nd voice. Multiple channel converters are also available from both vendors; the Q174 from is a 2-channel module with the same 1-MU width as the Q104 (it only became available a few months after my purchase - Murphy's law!).

This video shows a couple of external sound generators (also driven via MIDI) to increase the no. of voices for live sequencing/playing.

Nov-2013 - Some experiments driving the synth via CV instead of MIDI. This video shows a Doepfer MAQ 16/3 sequencer driving the 3 VCOs independently with their mixed outputs connected to a single EG & VCA, giving 3 simple voices. Twiddling the MAQ knobs came up with a nice pattern so it was tweaked and transferred to a Doepfer Schaltwerk. The MAQ CV outputs were then free to control a VCF frequency both directly and via an EG module, resulting in this video.

Another 2 voice video showing Sequetron recording and controlling the synth via MIDI, with a brief taster of the hard/soft clipping option in the Q109 VCF.

Feb-2014 - Sampling is another way of increasing polyphony. It retains the modular's sound at the expense of hands-on control, although the sampler can be fed back through the modular to regain some of this. Capturing the sounds/patches can be tedious depending on your sampler's automation capabilities; this series of videos show how the Sample Aid tool can help. A test session comprising a 21-note, 19-velocity multisample is available for E-MU samplers E-MU 4B FAT-format (approx 65MB); contact me for portable .sfz/.wav format.


DIY mods

The dotcom modules are fairly easy to modify - there are no surface-mount components and all panel controls & LEDs are connected to the PCB via push-on connectors. The simplest DIY mods (if you are not averse to drilling the front panels) are to add toggle switches to the internal PCB jumpers which already exist on some modules.

The jumper links are shown in the data sheets supplied with each module and provide various configuration options, e.g. the Q106 VCO module has two 1v/octave frequency inputs which are normally configured as independent inputs, but a jumper allows them to be linked together. This is useful if you want to drive multiple VCOs with the same pitch control signal -  you would normally have to use a split cable or connect them via a Multiples module, but when the inputs are linked you can simply daisy-chain them together. Adding a switch allows you to change this option at any time without having to power off the synth, remove the module and change the jumper. Some other jumper options are shown below.

The toggle switches can be connected to the jumper pins via push-on connectors (recommended for ease of maintenance) or soldered. can supply switches pre-wired to push-on connectors so if you're likely to need these, order them at the same time to save shipping overheads.

All module PCBs are mounted parallel to the front panel using stand-off pillars, so for single switch mods some DIYers have avoided drilling by removing one of these and using the hole for the switch. If you do decide to drill the panel, it is recommended to remove the PCB and all controls first to prevent swarf getting lodged and causing shorts later. Either way, there is limited space behind the panels so the layout may have to be a compromise... and be aware that toggle switches vary in size so the old saying applies: 'measure twice, cut once'!  Here's my DIY results:-

Q106 Oscillator
The left-hand SPDT switch toggles the two 1v/oct sockets from being independent inputs (default) to being linked together for daisy-chaining.
The right-hand SPST switch is meant to toggle the output voltage swing between -5v...+5v (default) & 0...10v, but is redundant on my setup as it only works with the Q141 Oscillator Aid module - rtfm doh!

Q106 VCO switches

Q109 Envelope Generator
The left-hand photo shows a SPDT on-off-on switch which gives medium (default), short & long time constants. Note this 3-way option also requires some PCB track cuts and soldering. A much simpler option is possible with just a SPST switch and no PCB mods giving 2 time constants: default or long.
The right-hand photo shows a SPST switch which toggles the output voltage swing between 0...5v (default) & -5v...+5v.

Q109 EG time switch         Q109 EG level switch  

Q150 Transistor Ladder Filter
This SPST switch turns the automatic level control on & off (default).

Q150 Ladder Filter AGC switch

Q107 State Variable Filter
This SPST switch toggles the clipping between soft (default) & hard.

Q107 Filter clip switch

Q105 Slew Limiter
This DPDT switch toggles between linear & exponential (default) response. Using a simple switch limits the linear response to the Up direction only (the downwards slew time is zero), but there is a PCB mod which overcomes this (see web).

Q105 Slew Limiter lin/exp switch

Q108 Amplifier
The top-left SPDT switch toggles the Gain control range between -5v... & 0v... (default), the top-right SPST switch toggles the Control 'off' level between -5v & 0v (default), and the bottom-right SPST switch toggles the Control signal range between ...10v & ...5v (default).
In hindsight, the top-right switch would be better if placed to the left of the Control knob - a case of not thinking it through properly!

Q108 VCA switches

Q124 Multiples
Not a mod, but a recommendation to label the existing switch to clarify its operation to avoid accidents - connecting outputs to outputs may cause damage.

Q124 Multiples switch label

To be continued...