AW: "Stacked" Power Supplies - any thoughts?

[Stopp,Gene]

Welcome back, Juergen!

Hope your holidays were relaxing.

As the control panels of the new modular get closer to completion, I
have been thinking about what I will do for the power supplies. What my
plan is for now is to complete the panels, then wire up and mount all of
the different circuit boards inside, and leave a terminal block in the
back to attach the power supply to. Then I will try various power supply
options external to the unit, probably starting off with my big bench
supply to verify proper operation of everything. Once I do that, I can
try other power supply arrangements until I find something suitable that
will fit easily inside.

As I had mentioned a while back, this machine is really a collection of
many of the circuits that I build back in the lab at my old job (those
fun Fibermux days) and set aside. So it is quite a mish-mash of unusual
circuits, not really your typical modular (which is a good thing, I
think). It will consist of:

Upper left panel:

Completely patchable ASM-1
4-input mixer
two reversible attenuators
AR envelope generator

Lower left panel:

4 linear VCA's
1 Quad Passive Attenuator
1 VCADSR (probably a CEM3310 or SSM 2056)
1 IBM PC 486 motherboard w/ floppy and HDD
Monitor, keyboard, mouse connectors
Sound card audio inputs and outputs
8-channel DAC controlled by PC motherboard
8 CV outputs
8 Gate outputs
MIDI in and out

Upper right panel:

8 VCO/VCA pairs, saw/pulse
1 Master VCO CV controller
1 Output mixer for VCO/VCA pairs
1 Quad tri-square LFO
1 Shepard Function Generator (8 ramp and 8 tri outputs)

Lower right panel:

Quad VC Bandpass Filter Bank (4 in parallel)
Switched Capacitor Filter
4-pole Lowpass VCF (cascaded 3080's)
Stereo Digital Audio Delay
Final Output Mixer
Power Switch and voltage rail LED's

The 8 VCO/VCA pairs, the quad LFO, and the filter bank are all circuits
on 4 partially-stuffed ASM-1 circuit boards. The VCO/VCA pairs are to be
used with the Shepard Function Generator. The VCO's can be disconnected
from the VCA's so that I can have 8 VCO's as a tracking pitch source and
an 8-channel interpolating scanner, if I want. The switched cap filter
is the "Quasi-Digital Bi-N-Tic Filter" by Jan Hall, from an old issue of
Electronotes. The digital delay is made from Crystal 18-bit ADC/DAC's
plus RAM, with a VC clock.

I am now thinking that I will do the following for power supplies:

+/- 15 from a Power-One bipolar 15-volt supply
+/- 12 and +5 for the PC motherboard from another Power-One supply
+/-  5 from yet another Power-One supply

The +/- 5 will be used to power the analog switches in the commutating
filter, plus some of the panel pot voltage dividers. The +/- 15 will be
used for the rest of the analog modules. Notice that I am planning to
use a linear supply for the PC - I really want to keep switchers out of
this box.

I'll try to scan up some pictures some time....

 - Gene

 ----------
From: Haible Juergen
To: DIY; Stopp,Gene
Subject: AW: "Stacked" Power Supplies - any thoughts?
Date: Tuesday, June 02, 1998 6:52AM

Hi Gene,

sorry for the delay, just came back from hollidays.

	>My question is about regulation stability - can this be an
issue?
Each
	>one of these supplies is a dual 723/pass transistor design. I
know
that
	>a single 723 has pretty good stability as far as maintaining a
constant
	>output voltage regulation under varying current conditions, but
how
	>about regulated-regulation, or even
regulated-regulated-regulation?
Will
	>stacking these supplies cause any cumulative noise on the power
rails,
	>or any other effect?

I would be careful. I bet you will run into some side effects none of us
has
thought
of before. Stability of coupled systems is a tricky thing. It might
work,
but I would
not rely on it. Besides, you waste a lot of energy because you have
three
times the
voltage drop over 6 regulators than over 2.

This is what I would do instead, If I got these 5V PSU's for cheap: I
would
modify
one to get a +/- 15V output, changing a few resistors (yes, for the 723
it
involves
a change of configuration, too), and exchange the capacitors to higher
voltage
types. Then you need a new transformer, of course. Good chance to go for
a torioidal, if there wasn't one before.

Ok, I don't know if it is practical in your case. The capacitors might
be
larger,
and might not fit in anymore. But I'd ckeck this option, at least.

If you choose the right xformer voltage, you can get almost the same
current

from one pair of regulators as with 3 pairs of 5V regulators.


JH.