Parasound P/HP-850 Preamp Problem - diyAudio
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Old 3rd January 2013, 03:29 PM   #1
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Default Parasound P/HP-850 Preamp Problem

I have not one but two P/HP-850 preamplifiers that are exhibiting the same problem.

On both units, on all inputs both channels come out the left output.

Example:

With both channels plugged in, all audio comes out the left channel, no matter how you turn the balance dial it all comes out the left. If you turn it center it's slightly louder than with it all the way to the left or the right.

With only the left input hooked up if you have the balance knob at center or left the left channel plays, with it turned to the right nothing plays.

With only the right input hooked up if you have the balance knob at center or right the left channel plays, with it turned to the left nothing plays.

This behavior happens whether you're listening from the headphone jack on the front or either of the sets of output jacks on the back.

Here is a download link to a copy of the schematic which I got from Parasound support. I can also take some pictures of the inside of the units if that will be helpful to anyone.

P/HP-850 Schematic

Any help with repairing these units is greatly appreciated.
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Old 3rd January 2013, 09:07 PM   #2
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I tried multiple sources just to rule out the source as an issue, and they all had the same problem.

However I just left the thing on and kept checking it periodically, a few hours later the one that I left on stopped doing it, but it's done it before in the past. The other unit will still do it if I hook it up and try it, so I wonder if the chip that handles the input/output routing is old and flaky or what.

Since it does it over both the headphones and the RCA outs I'm guessing that means it's probably in the input selector chip, volume/balance part of the circuit or in the first gain stage.
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