multiple power supplies in a modular

[Stopp,Gene]

Despite potential harsh remarks about the validity of these questions, I
think that one of the reasons for being on a mail list is to short-cut
the time-consuming process of tedious research. And taking these
questions as an example, sometimes only years of mistakes can lead to
wisdom. Some of the subtler aspects of power distribution can certainly
be stuck into the category of "Black Art".

A quick answer to these questions would be, "it doesn't matter that
much". My first (and biggest) home-brew modular has distributed raw DC
and groups of 7815/7915 regulators spread amongst the modules. Works
fine, no noticable problems. Another system has a home-brew supply made
from a LM350/337 pair. Also works fine. A certain really big Moog that
I've worked on (and probably will be setting up this weekend at the NAMM
show), belonging to a fellow whose initials are KE, has at least three
separate BIG power supplies in it, works fine, no problems.

>From my experience, if you use a nice hefty gauge of wire for your power
distribution, you'll probably be okay. Even the star-grounding concept
doesn't really give a substantial benefit if you have heavy grounding
(to a metal panel, for example) distributed throughout the modules.

VCO's usually *are* quite power supply sensitive. For example, the
Elecronotes VCO's in the ASM-1 have the sawtooth comparator discharge
level set by a 20K/10K resistor divider to +15. This means that varying
the +15 will vary the sawtooth reset point, causing a change in tuning
and probably scale factor as well. Noise on the power rail will cause
frequency jitter. Incidently, this is the point where the sync signal
comes in.

The ASM-1 draws about 80 ma on each supply, not counting any panel
controls.

Although there has been some discussion about the noise level of the
78xx/79xx regulators, the effect of this noise is rather subtle and may
not matter for some applications. A little jitter in VCO's might add a
little bit of analog "feel" to a sound. It's a subjective thing, so I
wouldn't want to impart any good or bad advice here. One thing I will
say, is that for my next few projects I have some Power General
723/passtran supplies set aside. I want my next machines to be as good
as I can build them, and take my time doing it. I think that it's a bit
like building your own car as a hobby - every little piece needs to be
chrome-plated and perfect.

 - Gene

 ----------
From: Roger Arrick
To: Synth-DIY List
Subject: multiple power supplies in a modular
Date: Tuesday, January 27, 1998 8:51PM

Fellow synth builders:

What are the possible consequences of having multiple +-15, 1 amp
supplies in a large modular system as opposed to a single 2-3 amp unit?

What's the general sensitivity of VCOs to power supply V?

What about tracking VCOs that are on seperate supplies?

I'm not so sure what a big modular would pull.  Does anyone know exactly
what a complete ASM1 pulls?  This would give me a place to start to
estimate current draw.

Has anyone built a modular with module-based regulators?

Any input on 723/passtran verses 7805/7905 designs?

Thoughts on "Star" verses "daisy chain" wiring?

Thanks,
Roger.


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