[sdiy] Modular patching rules

[Ken Stone]

I used to go for higher gate voltages, but I've been told that my 10V gate
signals through their 1k resistor were killing Modcan inputs. If that is
true, Modcan aught to be ashamed of itself. Since then I do 5V gates, with
the user able to swap resistor values if they like.

The best philosophy is to drive (output) at the highest levels that can be
safely used across platforms, but have your inputs designed to take the
nastiest thing anyone is likely to shove into it - e.g. +/-15V (we11...
+/-13V) swing from a saturating op-amp with no limiting resistor.

Ken

>Hi.
>
>Getting slightly indecisive here with the modular getting slowly 
>bigger. Some advice from the experts would be very welcome.
>
>Regarding gate and trigger levels, should I aim for +5V gate/trig or 
>+10V as a standard -  What do you guys do?
>
>A lot of the boards I've got waiting around (assembled or otherwise) 
>are EFM, which look like they *mostly* have 100k input impedance, but 
>are missing 1K resistors on the output (easy enough to fix). These seem 
>to often need +10V for gates,and up to 10V or so for control.
>Is 0 to+10V common for a module CV input range, or is it  worth 
>tweaking the CV control ranges to make them 0 - +5V? That would make 
>sense for a VCF being swept by a +5V EG for example, but if swept by a 
>±5V LFO, the LFO would need attenuating to cover the whole range 
>without dead zones at the top and bottom - maybe that's just standard 
>practice?
>
>The other issue with EFM stuff, is that frequently there is no op amp 
>summer on the audio and CV inputs.  I think they help with preventing 
>overvoltage in the circuit, although they  don't necessarily prevent 
>audio overload. Zeners would help with that. Is that way too 
>simplistic, or just plain wrong?
>
>I'm about to start really going for the modular with around 20  CGS, 
>homebrew and EFM modules built, and waiting to go behind panels, and 
>need to fix on some standards.
>
>Any thoughts appreciated.
>
>cheers,
>
>Dave the indecisive..... ( I think.....)
>
>
>
>On 10 Feb 2007, at 21:53, Tim Parkhurst wrote:
>
>>
>> Well, a properly designed modular shouldn't have too many problems.
>> You might want to check your gear (especially if you have a bunch of
>> home brew stuff), but the "standards" for modular synth gear are:
>> 100K input impedance
>> 1K output impedance
>> +/-5V Audio levels
>> 0 to +5V control signals (0 to +10V in some cases)
>>
>> You may also use +/-5V signals for control purposes. Still, none of
>> this should damage anything. Go ahead and patch a VCO output back into
>> one of it's FM inputs, or take the output of the VCF and see if it
>> will trigger your ADSR (it probably won't, but you never know). You
>> CAN get into trouble if you do something like run a +14V signal into a
>> system that is powered by +/-12V, but a signal over 10V is pretty
>> darned hot and really isn't necessary (and pretty rare unless you've
>> designed something strange). By the way, 25v p-p is only +/-12.5V. Not
>> too outrageous. Oh, and for reasons the EEs in the crowd can explain,
>> you WON'T get a +/-20V signal if you mix the +/-5V signals from four
>> VCOs in a system (in a system with a 15V supply, you won't get more
>> than that total in any case).
>>
>> None of this is guaranteed, but spend a few minutes with a scope to
>> make sure you don't have anything too completely crazy (like a +/-15V
>> signal coming out of a home made VCO), and then patch away.
>>
>>
>> Tim (not completely crazy, but I play one on TV) Servo
>> -- 
>> "Imagination is more important than knowledge." - Albert Einstein
>>
>
>
>
_______________________________________________________________________
Ken Stone   sasami at hotkey.net.au
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>