[sdiy] Custom Prophet 5 Power Supply (was - bad voltages)

[Gil W.]

Hi !

The transformer I used (Polysix one) seems to be as
low as only 700mA !!! I never tried a 3.2A trans. It
was actually rated 3.2VA ! My bad.

Anyways. No I got two options:

1. I found a dealer who sells the exact transformer
used in the Prophet 5 (same maker and model, new).

2. I can go to a transformer-maker and build a custom,
improved one...

Both options will cost me about the same.

What would you all recommend me to do ?

If a custom one, than what should I ask for ? It will
still need to fit into the synth case.

The transformer maker guy has told me he can let me
have:

- Some kind of screening on the transformer for less
noise when placed over pickup based instrument (still,
not toroidal)

- Make a few inputs: 220v , 240v, 260v - so I can
select the best input for the desired output voltage

- Up to about 100VA-115VA (that would be up to 3.2A)
within the same dimentions of the original one...

Thanks all for your advice !!






--- harrybissell at wowway.com wrote:

> 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
> > 
> > _______________________________________________
> > Synth-diy mailing list
> > Synth-diy at dropmix.xs4all.nl
> >
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> 
> 
> Harry Bissell & Nora Abdullah 4eva
> 
> _______________________________________________
> Synth-diy mailing list
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> 


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