[sdiy] paia 4700 power supply troubles

[Jay Schwichtenberg]

Way, way long ago when I had one of these I had to build a power supply out
of 78XX & 79XX regulators to get it to work. The PS had enough ripple on it
that the filter and noise source had problems.

Jay


> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of
> rkmoore at memphis.edu
> Sent: Monday, March 29, 2004 12:49 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] paia 4700 power supply troubles
>
>
> Hello,
>
> I'm still struggling to get these 4700 systems fully functional.  I've
> had problems getting the filters to work and there's a pretty
> significant hum through the output.  At first I thought that the hum
> was just due to grounding issues, but now that I've looked at the power
> supplies it seems that the troubles may be there.
>
> I looked at the output of the supplies suspecting abnormal ripple and
> found a 20VAC component.  This seems really odd to me, but I also
> noticed that there were no resistors in series with the primary
> filtering capacitors.  I would think that they would be necessary to
> smooth out the voltage.  The capacitors are new (I replaced the old
> ones) and the diodes check good.  Is this the way the output of this
> power supply should be?
>
> I checked the supplies loaded and unloaded and got similar results.
> The modular system seems to be functioning fine except for the filters
> and the possibly abnormal hum.
>
> Richard
>