MOTM

Thanks much for taking the time to share your info, Tom! And I've seen your
synth before and love it! :-)

John

-----Original Message-----
From: Tom Farrand [mailto:mbedtom@...] 
Sent: Wednesday, October 01, 2008 7:51 AM
To: JohnLeightonRice
Cc: motm@yahoogroups.com
Subject: Re: [motm] To wire or to not wire power supply sensing terminals???

How much current is the power supply required to provide?  What is the
wire gauge used to connect to your distribution point?  How long is
the wire run between the power supply solder lugs and the central
distribution point?  The answers to these questions, taken together,
will help answer the question as to whether or not one should employ
the remote sensing function.

The greater the current demand, the more volts that are wasted in the
wiring itself.  Larger gauge wire helps because it has a lower
resistance per foot, hence, a lesser amount of volts wasted for the
amount of current delivered.  The length of the wire run is also
related to the volts wasted.  Longer runs waste more volts.

Remote sense was designed into the power supply for a reason.  Will it
work without using remote sense?  The answer is "maybe".  Here's the
deal ... many VCOs use the power supply rail as the reference voltage
for the VCO pitch.  If the voltage is drifting up and down a little
because some other module is maybe lighting up LEDs according to some
LFO output, the reference voltage for the VCO is drifting.  That will
result in VCOs getting pitch-changed apparently without any input
patched.  If your VCOs did this would you conclude that "something" is
wrong?  If large enough wire is used to connect to the power supply
and the run lengths are not excessive, the VCO pitch drift will be
minimal (not audible).

If you do not use the remote sense, is it guaranteed that you will get
this drift?  No.  It depends on the answers to the first three
questions I posed at the outset.  If remote sense is used, does THAT
guarantee that VCO drift will be eliminated?  No.  Even with remote
sense it is still possible to wire a synth such that heavy current
consumption in one part of the cabinet will reflect VCO drift in
another part of the cabinet.  The number of variables that will
influence the outcome is significant.  Therefore, a definitive answer
cannot be stated with the limited information provided.


http://www.radio-flier.com/cabinet.htm
The above link shows what I consider a reasonable power distribution
method.  What cannot be easily seen is the remote sense wires going to
the black, Cinch brand terminal blocks on the right-hand side of the
cabinet.  I used remote sense and was pleased with the results.  I do
suggest that remote sense be used because it is provided for free and
it does help.  The only cost is a small bit of wire and the minimal
time required to connect it.

Peace
Tom Farrand



On Wed, Oct 1, 2008 at 2:08 AM, JohnLeightonRice <Drummer@...> wrote:
>
> In a DIY power supply thread on MUFF's forum here
> http://www.muffwiggler.com/forum/viewtopic.php?
> t=1200&postdays=0&postorder=asc&start=30 (look for matthias' first
> post about half way down) it was suggested that power supplies like
> the PowerOne models that have remote sensing terminals should have
> those sensing terminals wired up to the appropriate output terminals
> to make sure the output voltage is always the same when the load
> changes (adding or subtracting modules from the system would cause
> this I guess?) That way you don't need to readjust the ps trimmers
> after each change?
>
> I'm looking for second opinoins before I go ahead and do this.
> Someone said that MOTM power supplies don't have the sensing
> terminals connected and I also noticed on Richard Brewster's site
> here http://pugix.com/synth/portable-rack-cabinets/ that his DIY
> power supply doesn't have the sensing terminals connected either.
>
> If you look at the power supply pictures on the Synthesizers.com site
> it looks like they wire up the sensing terminals.
>
> So, is one way better than the other? Are both equally 'good'?
> Thoughts and recommendations appreciated! ;-)
>
> John L Rice
>
>