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

[GRAHAM ATKINS]

Gil,

You should be able to buy a suitable transformer "off the shelf".
Take Tony Allgoods advice and use a torroidal transformer. They
are more efficient and inherantly less noisy, thats why you see them
in upmarket Hi-Fi amplifiers.

Graham
On Nov 12, 2007, at 19:17, Gil W. wrote:

> 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
>>>
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>>
>>
>> Harry Bissell & Nora Abdullah 4eva
>>
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