Diagnosing/repairing hiss on PV-1 phono stage?

[GordonW]

Hi- I have a PV-1, in very good shape here- except that the phono stage seems inordinately noisy. By that, it has a lot of background hiss, that seems to be independent of what tubes are in it (it came to me with Sylvania 7025s in it- but I have also tried Telefunken 12AX7s in all three positions (which were pretty quiet when tried in a Dynaco PAS3 phono stage)- with no change in the hiss.

There's also a tiny bit of hum- but that's pretty minor, compared to the hiss. No appreciable hum or hiss exists in the line stage.

I suspect it may have something to do with the power supply, since it's about the same in both channels. Is there something about the regulation or the caps in the power supply, that can cause this? And, if so, has anyone had luck with rectifying the situation? My first inclination is to try re-capping the HV part of the power supply (C2 and C4A/C4B/C4C on the original schematic diagram).

Or, are there other "common" issues (resistors?) that can cause this, in this model?

Thanks!

Regards,
Gordon.

[admin]

Hi Gordon,

Welcome to the site. As for the problem. I, unfortunately, don't own the PV1 so can't speak from experience. The first thing I would do is make sure the hum is not a ground loop issue. That will cause a hum and will be independent of the tubes. We have the PV1 schematics in our database so you may want to pull that and see if any overt issue is identified.

Let us know what happens, best wishes.

[GordonW]

It's much more hiss, than hum. And, the noise is present even when shorting plugs are in the phono input. The preamp and amp both only have two-wire power cables- so it's not likely a ground loop...

Regards,
Gordon.

[roberto]

Hola Gordon, if I were you, I will change again the tubes. Bad tubes make hiss, and no other component does that. Why don't you ask this question to Mr. Jeff Fischel. He is now in charge of the Conrad Johnson Company, and he is very handy. He likes to help!

Happy listening!

[ronenash]

I don't have the schematic for the pv1 but given its age i am assuming there are electrolytic salads in the power supply. These all need to be replaced. Leaky caps can cause noise. Also look for resistors that changed color or measure wrong. Focus on the phone section of the circuit.