Archive of the former Yahoo!Groups mailing list: MOTM

Request for Knowledge: Powering the MOTM SynthesizerOriginal Message -----
From: Tkacs, Ken
I wonder if some bright, literate person on this list might accept the
challenge to really, clearly (and with pictures!) explain the options for
properly and safely powering a large MOTM system, now that the power
requirements have changed.

--LH--
I will be happy to take on this challenge. Since I just finished wiring the
NAMM cabinets (which include 5 volt power) and questioning Paul at length
about the new 990 power board, I "think" I have it all together But, let me
take 5 minutes to throw out some basics incase someone wants to disagree and
shed some lighb on the subject I had not seen.

1. There is NOTHING wrong with running AC power to the front panel switch.
Loads of consumer equipment on the market with UL and CE approval does just
that. The MOTM 900 does just that. However, lets select an appropriate
switch for the job. I suggest a nice 250 volt AC 10 amp minimum rated
rocker if you plan to switch multiple supplies. And, many of them are rated
for high in-rush to cover the initial spike while charging them big 'ole
caps. Sure, using the standard MOTM toggle would look nice. And, you could
get by with that kind of switch for a single supply. But, its just not
appropriate application in my opinion.

2. Fusing. For maximum protection of your supplies, each should be fused
independently at the lowest value that allows you to load your supply. If
you gang 4 supplies on one fuse and increase the size accordingly, you are
compromising the protection of the supply. If any old fuse big enough was
good enough, they would only make one size. Now, that means the fuses are
downstream electrically from the switch. So, you need another fuse, large
enough to carry all loads right where the power enters the synth. It is to
the the FIRST thing on the hot leg after the AC connector. Otherwise, if
you switch fails, you have a small fire until the house breaker trips.
Notice the MOTM power switch has the fuse built in.

3. Use big wire to the distribution boards. Get some stranded copper 12 or
14 gauge. Nuff said.

4. Connect earth ground to the power supply case. Lug the wire, pick or
drill a hole, take a #6 to # 8 machine screw and locking nut and tie earth
ground to the power supply case(s). This is not optional, it is absolutely
required. Don't tell me it works fine without it because I can show you why
it is bad (not to mention a code violation).

5. When adding the 5 volt supplies (or for some supplies with 5 volt
output (built in) bond the bipolar ground for the +/- 15 and the separate 5
volt ground together AT or VERY NEAR the supplies. Run separate grouns
wires from the 5 volt ground and the 15 volt ground to the distribution PCB.
BUT, do not assume that on a triple supply that these two ground points are
common. They are not on the power one supply that Paul sent me for the NAMM
cabinets. Don't cheat and run ome wire to the PCB and jumper them at the
PCB. Jumper at the supplies and run two ground wires. If you are adding
the little 5 volt add on supplies, bonding the two DC grounds between the
supplies is also required.

OK, my 5 minutes is up and my day gig is calling. I'll do some PDF drawings
and such later.

Larry Hendry