EML ElectroComp 101 – 1 volt per octave conversion mod

Update, 8/2019: we are now selling PCBS and kitsf that make it easy to install this mod! Click here for details.

This is a really fun synth! EML was a lesser-known American synth company competing with Moog and ARP during the 1970s and made some unique instruments. The EML-101 is a semi-modular duophonic synth similar in structure to the ARP 2600 and very unique and powerful. The bulk of our work on this involved designing and installing a circuit that allows the synth to accept standard 1 volt per octave-scaled CV via its “SEQ” input, as its oscillators have an unusual scale of 1.4 V/octave with a 4.6-volt DC offset.

We made the above video to show off our mod and the cool capabilities of the synth in general. In a lot of the clips, I’m using a Korg SQ-1 sequencer to sequence one of  the of the voices.

I also added a switch that bypasses the scaling circuit so it can still be used as it was originally designed. The circuit is a pretty simple op-amp based circuit to convert the scale of the input voltage and also add the offset. The 4.6 volt CV offset must be added to shift the oscillator into audible range, because the oscillators can all function as LFOs and if you were to just send 1 or 2 volts in, you would get an LFO range oscillation. The 4 oscillators and the fact that they can be turned into LFOs are pretty unique and allow you to get some interesting effects. You can also use all of them to cross-modulate each other, including at audio frequencies for FM effects.

ElectroComp EML-101
ElectroComp EML-101

One thing about these synthesizers is they use sealed potentiometers. This means they can’t be cleaned and if any of them start to act strangely, it’s best just to replace them since their insides are inaccessible. For example, when we got the synth, Oscillator 3’s pitch would dip dramatically every time the tuning pot was turned – a problem that was caused by the pot being dirty and after it was replaced the oscillator’s seemingly bad behavior went away.

Working on this synth was so much fun, it really made me want to get one for myself!

Work done: replaced power supply capacitors, replaced 4 faulty potentiometers, cleaned key contacts, replaced failed Darlington transistors in oscillators, added 1/v cv scaling circuit to SEQ input, calibrated to factory specs

6 thoughts on “EML ElectroComp 101 – 1 volt per octave conversion mod”

  1. I have a EML 101 and would like to have the 1 volt conversion mod.
    Is it possible to do this myself?
    Could you provide the parts and procedure?
    How much would it cost?
    Thanks. Louis Dosch

  2. How were you able to replace the centertapped sealed pots? Were You able to source new ones as I’ve been trying to figure out what to do with mine for a while now?

    1. It’s true, I don’t know of anywhere you can get them now. What we do is unseal and clean them. Use a small flat-head screwdriver and lift the metal tabs on the top of the pot. This is what holds everything together. With a heat gun, you can then heat the whole thing to soften the glue that seals it while using the screwdriver to gently leverage it apart just a little, just to the point that you have enough room to insert a small straw. Then clean with your pot cleaning procedure of choice. We use QD contact cleaner and compressed air followed by Deoxit F5 for lubrication. Give it a decent amount of time to dry before closing it up again.

  3. Hi Allison, very interested in the CV interface for my 101. Would you consider:
    1. Selling kit?
    2. Selling plans?
    3. Trade for Pratt Read bushings? Or other OEM parts ( CEM, SAD, P-R keys..?)

    Archive Sound

  4. Does anyone know if the EML 200 VCOs share similar topology/etc with the EML 100/101?
    Just wondering if this adapter should work with an EML 200 also?

    1. I’ve never worked on an EML-200, but I believe that the EML-200 VCOs require a “post expo” CV. That is to say, they don’t have an exponential converter built into them, and need to receive a CV that has already gone through the expo converter of your EML 100 or EML 101.
      I actually designed an anti-log converter PCB that we use for V/octave input mods on linear oscillator synths like Korgs and smaller CS-series Yamahas, and I suspect that if you chained this with the normal “EML-101 1/V Octave” scaling mod PCB I designed you would be able to control your EML-200 with a 1/V octave CV source.

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