Modular CV/audio levels.

Dave Kendall

Hi guys.

Going *slightly* mad with indecision here.....
I'm trying to settle on a standard for audio and signal levels for the modular.

So far ±5V looks like a good choice for audio, and having all modules able to take levels up to the rails (±15V ) seems a good idea.

But how about CV and gate voltages? The paia midi2CV8 puts out +10V gates and CVs, the EFM MIDIGATE puts out +5V triggers, and several homebrew/perfboard projects running on HCMOS will put out +5V gates. One advantage of +5V gates - I guess you can use the positive portion of a bipolar ±5V CV as a gate...... I have used a CGS style comparator to trigger some circuits, but would like to avoid always having to do that.

Some VCOs/LFOs put out ±7.5 volts - it seems a shame to attenuate them unecessarily, or is that not really an issue?

FWIW all the modules (12 behind panels, and a further 10 in various states of build) are from pcbs - a lot of EFM and CGS modules, with a few others - a Charlie lamm Irwin SSM2164 VCA for example.

I couldn't find any previous threads on this subject, and would really welcome any discussion, ideas and opinions about this, as it might help me come to some sort of useful decision, even if that decision is to live with different standards, and use level shifters and offsets etc. to deal with problems....... Shocked

cheers,
Daved and Confused

fonik · Posted: Thu Dec 20, 2007 11:49 am Post subject:

i mean, the question is rather how to configure the gate/trigger inputs.

do you plan to build any module that needs more than +4V as gate/trigger signal? if not you are fine since both, +5V and +10V, would trigger it...
if there are any modules that would need more than that: how many? maybe it's worth to modify these modules only and you are fine again?

Dave Kendall · Posted: Thu Dec 20, 2007 4:55 pm Post subject:

Thomas Henry · Posted: Thu Dec 20, 2007 8:47 pm Post subject:

The very first thing I did when I got into synthesizers was buy and study the complete Electronotes collection. I'm self-taught in electronics, so that was perhaps the wisest decision I've ever made in my life.

Anyway, somewhere in the collection is a very nice write-up from Bernie on the standards. Naturally, his treatment is logical and makes a great deal of sense. I've always followed his standards in my own work.

Thomas Henry

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

It's a funny business this signal level stuff. I've never given it much thought myself even though I'm mixing 12V en 15V modules but I've never had any problems anywhere either. Mind you, none of these modules will actually output anywhere near the rails. You'd have to build them with rail-to-rail opamps for that to happen.

In my opinion it's easier just to plug it in and hear what it sounds like. You're unlikely to blow anything up at these signal levels. To be honest, I have no idea at all what signal level my LFO puts out. I just plug it into whatever I need and use it. If the level is too high, I attenuate it. You'll most likely want to attenuate anyway. I find I never sweep anything over it's full range, so matching up the levels exactly will only achieve something I don't want...

Triggers are probably the only tricky thing, although I've never given trigger voltages in my modular a closer look. They "just work" anyway. Probably because most triggers only require a couple of volts and aren't easily overloaded either.

EdisonRex · Posted: Fri Dec 21, 2007 3:44 pm Post subject:

Dave Kendall · Posted: Fri Dec 21, 2007 6:54 pm Post subject:

Thanks for the thoughts guys.

I guess the levels issue is something I can probably afford to relax about in a modular, although the fixed architecture synths will take a bit more planning....
I've wondered about getting the Preferred circuits Electronotes set for a while now. I've just got hooked on saw animators recently, and many designs I've seen on the web hark back to an Electronotes article or 2.
I guess I'll have to see how the money situation is after Xmas and new year!

cheers,
Dave