A Little Hiss- Is it time to replace power filter caps?

[Noelstan]

Hi everyone! Until recently I had my CJ PV-7 running on a transistor preamp tape loop and from there out to the amp. When I went direct from the PV 7 to the tube amp, I heard a little hiss with my ear very close to the speaker! With the cd on pause I turned up the volume on the CJ and the hiss didn’t change that much so it is something I can live with. But I read that sometimes the noise in both channels that stays the same could be failing power filter caps! Also the Little Dot didn’t make any noise but that’s a different animal.

My unit has the power filter caps mounted on a side board, not the can! some are easy to get to but there are some that are not! Was this an upgrade preformed at a certain time in it’s history? Are there any other caps that I should consider? Has anyone ever gotten the main board out so they can see the soldering traces etc? I don’t think you can just remove a bottom “hatch” to get to them. I noticed the output terminal pads probably come off with the main board but what nightmare lies in getting that board out,if I need to? The unit sounds good. Is that little hiss in all -inputs-outputs- normal? Thanks in advance! All tubes replaced with 2 NOS mullards and 3 gen gold lions!

[admin]

Before looking for faulty components. Any chance this is a ground loop? It would be 60hz (or 50hz depending on your country).

[AnotherJohnson]

If it’s what’s properly called hiss, it is not a ground loop. Hiss is more like white noise ... random emission, not cyclic hum.

If it really is hiss, the usual culprits are things like

A small tube

Resistors

Electromagnetic radiation getting into a tube or interconnect

Dirty connections (resistance again)

Your caps are not the likely source of hiss.

But, if it’s really hum, as admin speculates, the caps are likely suspects.

[roberto]

Hola Noelstan, and welcome.
If you turn off the preamp, do you still have that hiss?
If you use different inputs, still have that hiss? In other words, use aux 2 or use tuner. Disconnect all the inputs of the preamp, and only the output of the preamp connected to your amp. Do you hear the hiss? I
AJ is correct saying that hiss is produce by small tubes. Your preamp use 3 tubes for the phono stage and 2 for the Line stage. V4 and V5 must be the exact tube number. The audio circuit of the PV7 uses five vacuum tubes of two different types: three 12AX7 (V1, V2 and V4) and two 12AT7 (V3 and V5).
Confirm the position of these tubes. 12AT7 usually are more hissing than the 12AX7.
To me, I am with AJ, a small tube could be causing the hissing. Brand new tubes, one could be hissing too. Only changing them could fix the hissing.

Happy listening!

[Noelstan]

Thanks to all!
No it’s a white noise hiss! I know all amplifiers have a certain amount of noise. The PV-7 is old but the board looks unmolested and almost new! The only questionable spot I can see is that around the small Zener diode array near the regulator has scorch marks. Not black but light brown. As I said all the tubes are new. They are exactly what CJ called for. The unit came with all EH tubes but I did not do a “hiss” test before replacing them with the Genalex Gold (12AX7) and NOS Mullard (12AT7) the ones made for the British military. They all came from Tubedepot.com

The hiss is present on all inputs and since it is a preamp with no headphone jack I have to have it hooked up to an amp to evaluate! The high hiss sound is only noticeable with an ear right up to the speakers. Maybe this is still in spec for an older tube preamp? It doesn’t bother me when listening of course! Could the unit be operated without the three phono section tubes to test? Thanks again, Noel

[roberto]

When you select aux, the phono tubes are not passing any signal through...only V4 and V5 are passing the signal. There is not need to take them out for a test. While selecting phono and you do want to do a test, them you must short the phono input. Just with an old wire having a couple of RCAs, just short them and you can do the test.

Happy listening!

[jeclk]

Hello,
I live in France and I have had a PV7 for a very, very long time.
but it has a problem, after connecting it a hissing sound appears.
I would like to upgrade it.
I took some measurements and on the capacitor in 0.01 in 600v
I have 25v!!!!!!!!!.
I would like to know the value on the pins of the regulator with the small radiator, it is the MJE 340
the 2 parallel capacitors of 2uf in 200v which surround the AT7 tubes, I have 78v on each.
if anyone can help me thank you

[admin]

Hello,
I live in France and I have had a PV7 for a very, very long time.
but it has a problem, after connecting it a hissing sound appears.
I would like to upgrade it.
I took some measurements and on the capacitor in 0.01 in 600v
I have 25v!!!!!!!!!.
I would like to know the value on the pins of the regulator with the small radiator, it is the MJE 340
the 2 parallel capacitors of 2uf in 200v which surround the AT7 tubes, I have 78v on each.
if anyone can help me thank you

Not sure what the voltage ratings should be but you think this is a bad cap? Is there any visible damage like bulging? Is the hissing in both channels or one? It's not a 60 hz hum, correct?

I suppose you could pull the caps and directly measure to make sure they are up to spec.

[jeclk]

yes indeed I don't know the values,
It is planned to change all the capacitors.
the whistling sounds on both channels.
on the other hand I took measurements on the 7812 regulator which is encapsulated in the radiator on one terminal I have 12.07v but on the other I have 19v, which seems strange to me. I am therefore also going to change this regulator.
I have a technical diagram of the PV7 that everyone must have, but it is blurry to see the component figures, I downloaded it from the site but it is the same impossible to find a clear diagram.
thanks for your intervention .
For the diagram the only solution is to ask C-J.
Could you ask for the diagram, you can see that the one on the site is cloudy.

[admin]

I don't have any official association with CJ. They do not release their schematics any longer and haven't for newer models period. CJ does all service in house only and won't send replacement parts. So if you want their input, then you pretty much have to send them your unit. Sorry.

As for the issue at hand. You can try and replace parts a few at a time, although a complete recap would probably be worthwhile considering the age of the unit. Not only would it give a good chance of fixing the problem, it would potentially give you a major improvement in sound quality.

It goes without saying that if you are going to replace so many components, it may be worthwhile to put those funds into a newer unit in the CJ line. Just something to consider.