FW: Measuring the current draw of a modular

Magnus Danielson magda at it.kth.se
Tue Mar 11 04:24:03 CET 1997

>>>>> "LR" == Lahlum-FLR111 Ross <ross_lahlum at msmail.wes.mot.com> writes:

 LR> OOPS! I just realized after thinking about it that if you have a + supply and a
 LR> - supply sharing a ground return, the currents from the two supplies will
 LR> cancel out in the ground line.  Doh!  So don't do your current measurement in
 LR> the ground return... Sorry if I misled anyone.

Eh... i'd say your sligthly out on the ice here... sure, it will
cancel to some extent, but in reality this will not be true since many
synths and other equipment is certainly not fully balanced. Just take
a look at the ASM-1 schematic for instance... it does use +/- 15V and
ground for power, but just the VCOs is unbalanced, and the ADSRs is
living between +15 V and ground...

So there is a high possibility that there is an (more or less) steady
current between the powersupply ground and signal ground.

These powersupplies look so darn simple but they have many traps to
fall in... then again, real good once still look so simple that you
don't see why they work well...

I still learn everytime I think about it and work with them...

Who has measured the output impedance vs frequency of it's PSU lately?
Who has measured the isolation (between chassi and signal ground)
impedance vs frequency of it's PSU lately?
I only ask! I haven't... but I would sure like to do it...

Who has measure the impedance vs frequency of it's (large) capacitors
lately? It's really interesting :)


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