[sdiy] modular synth "standards"

[Happy Harry]

Hi Kenneth (et al)


>From: Kenneth Martinez <kmartinez at bency.com>
>To: synth-diy at node12b53.a2000.nl
>Subject: [sdiy] modular synth "standards"
>Date: Wed, 21 Feb 2001 15:10:07 -0700
>
>Working on my first DIY synth project here, and I'm trying to make it 
>follow
>"standards" where possible (and yes, I know there's plenty of them to 
>choose
>from).  I realize there's a variety of physical connectors for modules, but
>I'm wondering mainly about electrical characteristics.  If I want to be 
>able
>to interconnect with various commercially-produced modules at a later date,
>looks like I should use a +15V/-15V power supply; and 2 grounds (as with
>MOTM).

That sounds good. Blacet and EFM use the same standard.
>
>So, what else?   What are "typical" p-p audio signal levels in the system?

2 schools of thought:

#1: All signal levels are Control Voltage levels... like 0-10V or
+/-5V or similar... so the onlt difference between a VCO as a signal
source and VCO as a control is the frequency.  This means that a lot
of signals have to be attenuated before a module, and amplified after
a module... (esp a VCF)... and this can lead to more complex and more
noisy circuits.

#2: Signal levels at line level... maybe 500mV to 1V pk-pk. This can go 
right into a mixing console without any attenuation.

I favor #1 but others make a good case for #2.  Some clown will
undoubtedly mention a #3 that I've forgotten ;^)
>
>My VCOs will scale using 1V/octave, although some other circuits are
>0.5V/octave, so I'm basically using 0 to +10V CV.  I've seen some mention 
>of
>negative CV, but am not sure how common that is...?

Negative CVs are very useful. Picture a vibrato on an oscillator. Its
Much easier to use a +/- voltage to make +/- frequency... than to add
the desired vibrato and have to retune the oscillator.  OTOH if you want a 
'trill' that would be a square wave of positive going direction
only. So you really want both.

This will apply mostly to LFOs... Sine and Triangle waves are often
bipolar, and square and saw are often unipolar.

Usually Envelopes are positive only... but some can be inverted and
offset.

If you collect from commercial modules, they will be compatible with
er... what they are compatible with... its no longer your choice.

H^) harry

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