[sdiy] That old modular power supply question (again)

[David G. Dixon]

Julian,

I would suggest either option 3 or 4.  In either case, you should go through
the schematics of your modules and look for places where one or the other
rail level is actually important.  For example, it won't matter to opamps
whether they are seeing 12V or 15V.  However, there will likely be lots of
places where the supply is being divided to obtain some specific voltage;
+/-5V, for example.  In that case, one of the two resistors in the divider
will have to be changed, unless there's a trimmer with a value big enough
(and enough headroom in the right direction) to make up the difference.
Another common example would be the divider (or the feedback resistor on an
opamp) which is processing the output of a comparator, perhaps to reduce a
raw pulse wave to the desired signal level.  In this case, the raw wave may
be +/-12V, +/-15V if a true comparator is used, or either one minus two
diode drops if an opamp comparator is used.  There may also be some stacked
diodes or zeners which were designed to clip or limit to some specific value
relative to one rail or the other.

I would say: make a decision one way or the other, and then go through each
module and make the necessary adjustments.  Don't just plug them into the
wrong supply and hope for the best.


> Or at least a variation on it...
> 
> I have a (mainly) 12v system, currently running off a power one psu
> trimmed to 12v.
> 
> I want to add a 15v section.
> 
> I have 2 options -
> 
> To add another power one psu (which i have anyway) trimmed to 15v to power
> the 15v section, using a completely sepperate power
> distribustion board / supply.
> 
> To change trim the existing power one to 15v and then add regulators on
> each of the 12v distribution boards.
> 
> 
> To me, option 2 seems like a better plan (although more work).
> 
> I can make up the distribution boards, and, id think that regulating down
> locally would give the best isolation between boards?  (im
> thinking bad doefper LFO modules that bleed onto the power rails)
> 
> I always hear of people running into troubles trying to power a modular
> with two power supplies also.
> 
> Anyone have any comments?