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Subject: Re: [yamahacs80] HIgh Pitched Whine

From: Bob Stewart <bob@...>
Date: 2015-06-12

This is pretty loud.
And as I said, it seems to be eminating from the PSU... As in you can hear the power transistor on the -15Vrail whining away, if you've got the audio out disconnected.
But it manifests on the audio out as well. Round about 5KHz I reckon.




On Thursday, June 11, 2015, 'Stephen Parsick' wavecomputer360@... [yamahacs80] <yamahacs80@yahoogroups.com> wrote:
 

I recently read about a modification that was done by Kent Spong which involved re-routing the cable loom because it would produce some kind of high-pitched whine. Maybe Kent could elaborate on his?
 
Mine does that as well but it's only audible when playing lower notes.
 
Stephen
 
Gesendet: Donnerstag, 11. Juni 2015 um 17:06 Uhr
Von: "bob@... [yamahacs80]" <yamahacs80@yahoogroups.com>
An: yamahacs80@yahoogroups.com
Betreff: [yamahacs80] HIgh Pitched Whine
 

Hi


Still having issues with this CS50 PSU.

I've got a horrible high pitched whine all over everything. If I turn the amps off, I can actually hear this noise emanating from the PSU.

If I put a probe on the lines, I've got oscillation on both the + and -15V lines. Much worse on the -15V line.

I've recapped it, changed all the transistors, and diodes (Apart from the rectifiers)
Changed the 4458, but no change.

What's really odd is that if I touch the anode of the -15V zener (Opamp supply) with a scope probe, it collapses the Opamp supply.

Also... If I remove voice cards 3 and 4 from the rack and the problem goes away... even though they're still connected to the power.

Any incite, or suggestions  most welcome... I've got to get this thing sorted in a couple of weeks, so a client can use it on a session. :-s