[sdiy] Prophet 5 power supply news...

[harrybissell at wowway.com]

The beefier transformer ~could~ still help you, imho

Larger transformers have more core, that equates to a
better load reulation spec (it will run closer to the
designed voltage at a wider range of currents than a smaller
unit would) Smaller transformers are run more agressively
with a higher no-load voltage.

The lower flux in the transformer would probably result in
less acoustic noise (audible hum) than a smaller transformer.

There would be a little more loss from the power line (higher
magnetizing current) for the larger unit, not that you would
notice or care imho...

H^) harry



On Sun, 11 Nov 2007 11:50:32 +0100, ASSI wrote
> On Sonntag 11 November 2007, Gil W. wrote:
> > Now, when I connect the entire synth, with no CEM and
> > CA chips, I get correct -15v and about +14.90v,
> > stable. But as soon as I play the keyboard, I can see
> > the +15v rail voltage droping again to about +14.50v.
> > Stop playing and the voltage rises back to +14.90v.
> 
> Have you ever checked how much current is drawn on each rail (don't 
> forget to measure the return current on GND as well)?  There simply 
> may be some more circuits that draw way more current then they 
> should.  It's no use poking about in a polysynth if you have no 
> measurements telling you where to look.  If your P5 has seen some 
> abuse from the power supply, then it is quite likely that there are 
> even more damaged components than the few you've replaced so far.
> 
> > So can we assume that simply the Polysix transformer
> > is not up to task ? or do you think there could be
> > other issues that makes it behave like that ?
> 
> The P5 schematics call for 36VCT, 2.8A, you've stated your 
> transformer is 36VCT, 3.2A.  Again, if the spec you've given is 
> correct, then a beefier transformer does not help you.  If the synth 
> draws too much current the regulators would get overloaded anyway. 
>  How hot are they getting, are they properly heatsinked?  If they 
> get too hot, they will go into thermal shutdown.  Before I'd get a 
> custom wound transformer, I'd borrow an oscilloscope and look at the 
> ripple on the supplies with and without load, before and after the 
> regulators and the voltage waveforms out of the transformer.  That 
> should tell you if the problem is before or after the regulation.
> 
> Achim.
> -- 
> +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk]>+
> 
> SD adaptation for Waldorf microQ V2.22R2:
> http://Synth.Stromeko.net/Downloads.html#WaldorfSDada
> 
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Harry Bissell & Nora Abdullah 4eva