Looking for advice on power distribution

Don Tillman don at till.com
Sat Apr 13 20:19:11 CEST 1996


   Date: Fri, 12 Apr 1996 12:36:34 -0400
   From: Bob Zimmer <bzimmer at voicenet.com>

   In designing a fair size modular system of 30 or so modules, it has occurred
   to me that there are two ways to distribute power to the separate modules.

   First, a large linear or switched supply (3A or so) sending power down buss
   lines that are connected to the modules.

   Second, a large rectified supply (3 to 5 amp xfmr, bridge rectifier, main
   filter cap) sending power down buss lines that are connected to the modules
   and then having separate small regulators (78L15, 79L15, 78L05 etc) with
   small caps surrounding them on each board.  This would add about $1.50 to
   each module, but if it would be a better and safer approach, it would be
   worth it.

   Any comments on which would be the best approach?

   I realize that this is mundane to EE's, but for those of us who aren't ...

It's actually a very reasonable question!

Of course the answer depends entirely on the power supply interaction
of the specific modules and how much you care about the quality of the
whole production (Though, if you're going through all the trouble of
building a modular, I'm guessing you wouldn't want to scrimp on
quality anywhere.)  

Anyway, in general...

I would do both.  Having tiny local regulators is a big win because
there's no interaction between modules, and you have less thermal
drift compared to one big regulator chip heating up.  And they're dirt
cheap.  Having one central regulator is a win because you get
system-wide overcurrent protection and you need smaller filter caps
(as part of the function of the regulator is to remove ac ripple).

So I would do both, using the big central regulator as a
pre-regulator.

An extra advantage is that the tiny local regulators will individually
dissipate less heat as their input voltage can be regulated to just
above the drop-out point.

   Date: Fri, 12 Apr 1996 13:23:00 -0600
   From: majmoog at leonardo.net (Kevin Lightner)

   The most important and overlooked aspect I've found when building large
   modulars is a very good ground between all the cabinets and modules. These
   ARE voltage controlled synths remember. :)

Yesyesyesyesyesyes.  Absolutely.

   Although I've seen some great regulation specs on switchers, I still can't
   bring myself to sticking one in a modular synth. Power one, Condor,
   International Power are my favorite linears.

A switcher is only reasonable for the case were you have a sustantial
amount of power being used by non-audio stuff.  The Chroma is a good
candidate because of the huge amount of power that the microprocessor
circuitry eats up.  A Mellotron is also a good candidate because of
the motor.

  -- Don




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