IVANOHÉ I The analog beast

Construction of an analog modular synth

Some years ago I start this project and, if everythings go right, it should take most of my live to finish : Building a Modular Synth.

Photo of the beast

Front

Inside

List of modules

• 3 Electronote Tri-square VCO PCB
• 1 ssm2044 VCF
• 2 VCA
• LFO
• 2 ADSR
• 10 stages sequencer
• 1 MIDI/Control voltage converter, CV/MIDI and trigger (drum pad)/MIDI
• 1×2 Inputs Mixer
• 2×3 Inputs Mixer
• 1 Sample and hold
• 1 Ring modulator (AD633JN)
• 1 Timbre modulator
• 1 Octavizer
• 1 Differentiator
• 2 Inputs modules (amp)
• 2 Outputs modules

some sounds of the synth.

Why doing this?

Why spending so much time (hundred of hours) building an analog monster from the past, which can probably appear in a Frankenstein movie, when you can get a wonderful digital synth/sampler instead?

The answer is simple. A modular Analog Synth is the perfect amusement park for someone like me who like to create sounds and build electronic stuff. All the knobs (about 120) and the inputs/outputs jacks (about 161) give you lots of possibilities to create electronics sounds (or to get a good headache sometime :) ). For example, nothings prevent me to do Frequency Modulation (FM), or Amplitude Modulation (AM), of a VCO with my own voice. Try to do that on some digital synth!

Some building tips

If you ever want to build your own analog synth, take note of the following:

• You will save some money by building a modular synth yourself. However, it takes LOTS of time to do it. If your time is precious, you are better to buy one instead.
• This is not a beginners project! If you never have done soldering (electronics, not plumbing!) you are better to start with something simpler like a Paia Kit.
• Some knowledge about electronics is required. Even if you follow the building instruction to the letter, your first board won’t work the first time (Murphy’s law). You will have to debug the board yourself (burned chips, wrong part, cold solder joint, capacitor on the wrong side, etc).
• Even when the circuit board is working, the work is only half done! Doing the front plate, drilling hole, connecting everything to the board, labelling, etc, take a lots of time.
• You need at least 4-5 modules before being able to use the synth. At least a VCO, VCA, VCF, ADSR and some sort of control voltage generator (Midi to CV maybe or an analog sequencer). You won’t have lots of fun and sonic possibility after your first module is done.
• Watch out for the synth builder syndrome! You may not have time anymore to do complete musical song: Doing experimental sound can take all your remaining time (this is not necessary a bad thing).
• This is a LONG project. Yes I know, I already said that, but this is the most important negative point.

If I didn’t discourage you, here some more positive things and tips:

• When the basic modules are done (VCO, VCF, VCA, ADSR, CV), things start to be very interesting. Adding a new module will significantly multiply the sonic possibility!
• To save some time, try to plan ahead of time what the next few modules will be. For example, if you plan to eventually do a second VCO, do the front plate at the same time you do the first one. When you will do the second VCO, the front plate will already be waiting.
• Power Supply tips: You will have to build your own power supply since you may need to use -15,0, +15 volts. This is the heart of your system, so you are better to do it right! Plan for something that can give you some current (at least 1 AMP on each rail). That way, you won’t need to worry after adding lots of module. On my synth, my first power supply stage (transfo, rectifier, diode bridge + big capacitor) give a rough + – 18 volt. After that, it is distributed to many regulator that do the clean + – 15 volts. Having this configuration allow a better noise immunity since not all your module is on the same supply. Also, if one module fail and short the supply voltage (this has happen to me), only the other module on the same regulator will be temporary affected. Finding the broken module will be much easier. For the best system, you can plan for a regulator on each module but this is more work to do (and more money to spend).
• PCB Tips: Whenever you are doing your own PCB with copper plate + chemical, having them done by a company or if you just using the kind of copper board with pre etched pattern, try to space your components and leave some extra inch on the PCB. It will be easier to debug, easier to modify or add a small feature, and you will have some space to fix your bracket in place to attach to the front plate. I made the mistake of doing really small PCB to save some money… Now I pay for it. You should see how creative I must be to find place to fix a bracket. Another one: I was not planning to fix the PCB to the front plate for most of my module: just the wires connected between the PCB and Front plate were holding this all together. This is not good!
• There is 2 popular type of connector: Banana plugs and phone plugs (1/4”). Banana plug have the benefit of being stackable. This reduces the amount of female connector need on the front plate. They are less expensive too. Phone plug have a better noise rejection since there is a shield on the wire. However, the audio voltage levels are in the 5-10 volts range, so a noise of some mV will probably be not noticed. This is why I choose banana plug.
• Buying a scope is heavily recommended. The good news is you don’t need the latest one. A cheap one or used one will do the job nicely. Remember that we are dealing with audio rate frequency (max is around 20khz) so any scope can “see” that. I have an old second hand Tektronix (Lamp based) that’s doing the job correctly.
• It’s really good to hear the result your own hard work. The sonic quality is excellent even for something build by hand! (Subject to the circuit you choose to do)
• You will have something unique in the world.

Where to Start?

Good question. This is the equipment you need:

• Soldering iron: I suggest a good one (middle range). Don’t take a real cheap one, you’ll regret it!
• Desoldering tools: A simple manual pump or some desoldering bread. Very useful!
• Multimeter: Nothing fancy here. A cheap one will do the work. I have an analog one and it does the job. The kinds of measurement done most of the time are continuity test and DC voltage reading.
• Scope: Optional, but heavily suggested. (See tips higher)
• Tools: Long nose pliers, wire cutter, screwdriver, Dremel (to do the hole on the PCB), drill (to do hole in the front plate). A note about drilling: Doing hole in aluminums front plate is difficult with a hand drill. The best tool is a column drill; it’s so easy to do a good job with that!

Layout, schematic, pcb.

• Barry Klein’s book is a good starting point.
• ASM-1 : This is a must see project (see the links)
• The synth DIY mailing list is a good place to ask question, read about the subject (see the links)
• I have a PCB Layout for the Electronote Tri Square VCO (from M. Klein book, also in Electronote publication). You’ll need one of those reference for part list.