MOTM

Hi,
I'm looking for help from someone with experience with a large system.
The first question concerns power supply location.  My cabinet (which 
was built previously for another use) has 5 rows of 34 U spaces each 
for a total of 170 module spaces.  (Yes, It's BIG)  I do hope to fill 
this thing eventually.  I've got a large linear power one supply 
capable of supplying plus and minus 5 amps at plus and minus 15 volts, 
(Is that a double negative?) which I figure is enough to power the 
whole cabinet filled.  The question is where do I put it.  Has anyone 
had negative experiences in the way of hum or electrical noise from 
mounting their power supply near the back of the modules?  Would it be 
better to have the power supply external and connect it, say with a 
hubbell?  I'm not worried about hum from the AC lines into the thing, 
my studio is completely wired with balanced line AC.

Second question is what about cooling?  My cabinet is unusual as it 
has a closed back.  I estimate that the modules will generate about 90 
watts of heat when the cabinet is filled.  If I mount the supply in 
the cabinet as well I'd probably have about 180 watts to dissipate.  I 
don't want my modules to act up due to heat and cutting the back out 
of the cabinet is out of the question.  Has anyone had any experiences 
with cooling problems?  I could cut some slots in the top and bottom 
of the cabinet, or I could mount a couple of whisper fans and baffle 
the inside to ensure circulation over the backs of all the modules.  
I'm really not in favor of the fans, although practically every synth 
I have has one, in a recording studio environment all that fan noise 
adds up.  Of course that can be overcome by playing really loud :)

One other thing;  I love the idea of naming a synth Darmok!  It is 
inspired!  I suppose it only plays in metaphors.  I've been trying to 
think of a name for mine.  Perhaps I will have to start watching old 
Star Trek episodes.  The one where Picard plays the flute comes to 
mind.

Anyway thanks in advance for the help.
Paul Haneberg

> was built previously for another use) has 5 rows of 34 U spaces each
> for a total of 170 module spaces.  (Yes, It's BIG)  I do hope to fill
> this thing eventually.

((I'm looking for that Lexus LS430 brochure, checking trade-in value of the Taurus))

>question is where do I put it.  Has anyone
> had negative experiences in the way of hum or electrical noise from
> mounting their power supply near the back of the modules?

In the back, in the bottom, in the *center* of the cabinet. Then you make a wiring "tree" with
14ga wire. The tree goes "up" to each row. You use barrier strips/spade lugs to tie to each
'row'. Then, you place 2 MOTM-960s per row, to to the 'left' and one to the 'right' at the 1/3
and 2/3rds distance from the ends.

Then, you can use the 20" cables without problem, and you can disconnect a row from any other
row.

Now, the important thing is NOT TO DAISY-CHAIN. In other words, each row has 3 SEPERATE WIRES
back to the bottom "Master Barrier Strip". I would get 3 wire colors like blue, yellow, and
black. Use black for the grounds.

To conclude: on the bottom with the Power One is a honkin' barrier strip, like Allied #607-1352.
This is a 'double row', 25 position. You need 5 x 3conductor = 15 terminals plus 3 to the supply.
Each row has say a 9-position: 3 in, 3 out Left, 3 out Right. Each row has a pair of wiring
harnesses with 0.250 FASTON females on one end (connects to '960) and spades (screws into barrier
strip), all 14ga stranded wire. I hope I'm making sense, it's been a long day. B-1 bombers and
squads of F-16s keep flying patterns over my house. Hmmmmm.......

The excercise is left to the reader on proper connections, ty-wrapping, etc.

>
> Second question is what about cooling?  My cabinet is unusual as it
> has a closed back.  I estimate that the modules will generate about 90
> watts of heat when the cabinet is filled.  If I mount the supply in
> the cabinet as well I'd probably have about 180 watts to dissipate.

YIKES!!

OK, this is where you need thermal management.

First: is each row 'sealed' from the others? In other words, are the rear edges coplanar, so that
if a back is attached, heat from say row 2 can't "flow up" into row 3? If this is the case (pun
alert), then you have to VENT EACH ROW. This is probably the best way, because it prevents a
temperature gradient in the case, and prevents the top row from getting all the heat.

Now, the Power One will get 1/2 of that heat. And, that heat is concentrated on a small area, of
the Power One chassis (first lesson you learn in Thermo 101: heat and temperature are NOT THE
SAME THING). So, you need to mount the chassis on 3/4" standoffs. If you bolt it flat to the
bottom, this is what we refer to as "a bad idea". You want air to flow all around the supply, and
you DON'T want the bottom of the cabinet as a heat sink.

Next, you want to cut a rectangular opening in the back cover, and STICK THE POWER ONE CHASSIS
OUT THE BACK, exposing the power transistors to the "outside". This is where 80% of the heat will
go. It will face the wall, who cares it is looks a little odd. It doesn't make sense to "lock it
up" inside a case, then wonder why the inside temperature is 170F.

You will not need fans.

Paul S.

Paul's tips are graphically illustrated here, if you haven't already 
seen the Synth of Doom's power distribution scheme:

http://www.users.qwest.net/~daveb2/distribute.htm
http://www.users.qwest.net/~daveb2/distribute_sod.htm

As far as closing up the back: you could cut vent slots at the top 
and bottom to help carry away any heat. Although the back of my cab 
is open, the power supply doesn't seem to generate any heat worth 
mentioning.

Moe

>>>>>>>
>question is where do I put it.  Has anyone
> had negative experiences in the way of hum or electrical noise from
> mounting their power supply near the back of the modules?

In the back, in the bottom, in the *center* of the cabinet. Then you 
make a wiring "tree" with 14ga wire. The tree goes "up" to each row. 
You use barrier strips/spade lugs to tie to each 'row'. Then, you 
place 2 MOTM-960s per row, to to the 'left' and one to the 'right' at 
the 1/3 and 2/3rds distance from the ends.
<<<<<<<

> 
> In the back, in the bottom, in the *center* of the cabinet. Then you make a wiring "tree" with
> 14ga wire.

Just for clarification, if using 14ga. from a Power One to distribution
terminal blocks and/or 960's then 14 ga. should be used from the Power One
to the power switch and connector/fuse (?).
Jeff

For AC wiring, you use 16ga, 600V rated insulation wire.

Paul S.

----- Original Message -----
From: "Jeffrey Pontius" <jpont@...>
To: "Paul Schreiber" <synth1@...>
Cc: <motm@egroups.com>
Sent: Saturday, December 01, 2001 1:53 PM
Subject: Re: [motm] Power Supply Hum and Cabinet Cooling Questions


> >
> > In the back, in the bottom, in the *center* of the cabinet. Then you make a wiring "tree"
with

> > 14ga wire.
>
> Just for clarification, if using 14ga. from a Power One to distribution
> terminal blocks and/or 960's then 14 ga. should be used from the Power One
> to the power switch and connector/fuse (?).
> Jeff
>