CV - voltage distributor for synth

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Freq Band

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I am almost done building this:

http://www.musicfromouterspace.com/analogsynth/cvdistributor.html

But I am putting 3 of these circuits on one board, to split 3 different CV voltage types (Hz/volt, gate, and trigger), needed for my diy modular.

QUESTION:
The PSU input caps...are listed for the one TL084. What if I'm feeding 3 chips? (+/- 12v)
Do I need to duplicate (add) the caps (and same values) before each chip's power pins? .....or is the one input set enough, and then power is distributed to all three TL084's.
I have a hunch I'll need to increase the 1uf to be higher if it's feeding 3 chips.. I'm sure there is some equation that will tell me, but I'm guessing 10uf might be ok?
(or would there be one set of 'lytics, and 0.1 bypass caps on every chip?)
The 2 datasheets I have make no mention of PSU input caps.
--------------------
'NOTHER Q:
What would I do for "protection".....diodes somewhere?,,,,after all, I am DIY'ing this, and could foresee a CV short, now and then.

=FB=

cvdistributor.gif
 
[quote author="CJ"]somebody "f"ed up that shemo, s/b

0.1 uf bypass

pw supply caps s/b in the 1000's of uf[/quote]

Nah, this is synth work, which is not picky, not only is this synth work, it is CV work which is even less picky. Your power supply which is offboard has the big cabs, or should. This is standard for modular synths, couple small uF bypass caps on the power input for each modual. Individual bypass caps for the opamps is almost never needed here.

adam
 
What does it matter if you short the CV? It happens everytime you plug in a phono jack. This has been going on for ages in modular synths, it does not hurt anything. Some people feel it is bad and they use banana jack instead, but 98% of the time it is not a problem.

adam
 
I got paid to maintain Arp and eMu modular synths, and never heard of a control voltage splitter. Just wire everything in parallel. All outputs are 1K, all inputs are 100K. No harm can possibly happen, and the "loading errors" are negligible. You can't hear few-percent error of amplitude, and pitch is so fussy and drifty that you have to hand-trim every minute or so anyhow.

> one set of 'lytics, and 0.1 bypass caps on every chip?

Assuming your main power supply is clean, yes that is a good safe rule. 0.1 at each chip and say 10uFd-47uFd on each board.

For the mild TL074 series, if I could get a 22uFd cap somewhere so that there was less than 4 inches of conductor to every chip, I wouldn't even use the per-chip caps. (They can be essential on less-stable chips.)

If you put the chips in sockets, TLO74 chips are too cheap to worry about "Protection diodes". And if you put 220 ohms in series with each power line (between the main supply connectors and the electrolytic caps), odds are that the TL074 will survive reverse voltage.

What the heck is the 1K||0.001uFd network supposed to do? (For that matter, the 100 ohms on the output is pretty pointless on TL074.)
 
I got paid to maintain Arp and eMu modular synths, and never heard of a control voltage splitter. Just wire everything in parallel. All outputs are 1K, all inputs are 100K. No harm can possibly happen, and the "loading errors" are negligible. You can't hear few-percent error of amplitude, and pitch is so fussy and drifty that you have to hand-trim every minute or so anyhow.

This is fallout from MOTM modular synthesizers, everything overbuilt and excessive. 4 jacks wired together as a multipul is no longer good enough for people. I think the logic is to cut down on cross talk between moduals, which never seemed a real issue to me.

What the heck is the 1K||0.001uFd network supposed to do? (For that matter, the 100 ohms on the output is pretty pointless on TL074.)

I could not figure that out either. I stopped trying to figure out Synth DIY circuits a long time ago, they do alot of goofy things like this. Learning electronics became alot easier when I stopped looking at this stuff as well. Maybe he just felt a need to put something in the feedback loop, just tieing the output to the inverting input is just to boring. Emitter followers seems like it would make more sense, and be alot simpler, but they never seem to use those nice simple transistor circuits.

adam
 
The only comercial synth I remember having "distribution modules" is the Synton modular, a pretty rare modular synth from Holland. I still have that module somewhere...

Best Regards,

Synthi
 
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