PV10 AL with noise problems

[Ovitzi]

I have e Conrad Johnson PV10AL. The one with three knobs in the front.
I have recently changed the tube sockets and tubes because of some squeaking noise problems. And it got way better. But I still have some noise. Its a hissing noise I can hear all the way to listening position when the music stops. Its an constant level, no difference when i turn the volume knob. Do you think it about time to do some capasitor changes? And which capasitors to change?
Can there be an issue that there are now earth/ground wire on this?
I have the parts list and the schema, and it looks like the capasitors in the line section have a bigger value than the part list says. It should be 2 uF, but it is 4 uF. Is that a problem?

[admin]

What frequency is the hiss? If it's 60 hz (US, not sure what frequency the power supply is in Norway but I do believe it is 60 hz as well), then it may be a ground loop.

[Ovitzi]

We have 50 Hz here in Norway. But it is more like pink noise, like a fm radio out of tune.

[AnotherJohnson]

The noise you describe, in my experience, may be due to a tube just being noisy (even if new), or dirty potentiometers or switches.

A thorough cleaning of pots and switches is free, and may solve the problem. If it doesn’t, try some other tubes if you can.

FWIW, the PV10 is old enough to be ready for its second recapping. If it were mine, I would R&R them all. Looks like electrolytics. If they’re not all bad now, they will be ... might as well take care of it when you’re in there snipping and soldering anyway.

[roberto]

Hola Ovitzi,

I am too with a noisy tube. Is the noise on both channels at the same time, and also the same level (SPL)?

[Ovitzi]

I have tried to change tubes, from Sylvania, to Psvane. Same noise. Both channels. Volume and input selected does no difference.

[admin]

I know you said you didn't think it was a ground loop but I wood rule that out 100%. Do you have a ground loop isolator rca cable or a calibration mic that can identify the frequency of the sound accurately?

[AnotherJohnson]

Can there be an issue that there are now earth/ground wire on this?
I have the parts list and the schema, and it looks like the capasitors in the line section have a bigger value than the part list says. It should be 2 uF, but it is 4 uF. Is that a problem?

You mention changing sockets as well as tubes.

What you describe as hiss is generally pink or white noise rather than an easy to distinguish humming sound.

If the free solution of cleaning doesn’t have any effect (clean the new tube sockets by removing and reseating the tubes once or twice), then tubes themselves would be the next suspect, even if you installed new ones. It is a characteristic of small tubes, and it is why known quiet tubes are so desirable. (Be sure to clean your input jacks and interconnect terminations too).

Replace one tube at a time to look for the noisy one.

You have an extra bit in play here. You’ve soldered stuff, and it sounds like you’ve also added a ground lead out to your mains.

Since you describe it as hiss, and not hum, I am less enthusiastic about the idea that it’s a ground loop ... but you certainly want to be sure you don’t have a ground loop, and with your addition of a ground wire, you might wonder about this.

I would point out that solder jobs are often audible, and often are described as an elevation of the noise floor, so this might be an issue. Sockets themselves can also be noisy, but cleaning by reseating the tube is usually enough.

Regarding your question about the caps, I think the values would not create the hiss. But they sure look old and ready for R&R.

You imply that your restoration project so far did produce an improvement. That’s great!

Can you get the PV10 all the way back to its original performance? I dunno ... resisters don’t age out as a rule, but some resistors are noisier than others. Have any resistors been replaced with non-stock types? The hiss from resistances is why cleaning and soldering technique are so important. Is there a darkened resistor (suggesting that it’s on the way out)?

FWIW, cleaning, tube, failing or out of spec resistors, and solder technique are all capable of producing hiss. Cap failure is more likely to produce hum.

A bit of advice from CJ to reduce noise is to plug source, amp, and preamp into the same outlet. In the era of the PV10, it was noted by CJ that you could change noise floor by inverting the power cord.

Ha det godt!

[plurn]

I have e Conrad Johnson PV10AL. The one with three knobs in the front.
I have recently changed the tube sockets and tubes because of some squeaking noise problems. And it got way better. But I still have some noise. Its a hissing noise I can hear all the way to listening position when the music stops. Its an constant level, no difference when i turn the volume knob. Do you think it about time to do some capasitor changes? And which capasitors to change?
Can there be an issue that there are now earth/ground wire on this?
I have the parts list and the schema, and it looks like the capasitors in the line section have a bigger value than the part list says. It should be 2 uF, but it is 4 uF. Is that a problem?

Since the noise is constant despite the volume level, I would think the noise would be produced after the volume control takes effect on the schematic. So this would be the area to look at.

Another possibility is that there is nothing wrong and the hissing noise is just the inherent noise for this unit and you have a bad system match. All electronics have some noise - some more than others. You have not mentioned what other equipment you are using. If you are using a high gain power amplifier eg 32db, or high efficiency speakers eg 95db or more, or in a worse case both, then any little hiss noise from the preamp will be very obvious and audible. If in a small listening room - even worse.

To continue the example, the same preamp in a system with a power amplifier with typical gain, eg 26 or 28db, and very inefficient speakers eg 83gb, in a big room might sound very quiet at the listening position with no hiss audible.

Let us know what your other equipment is so we can advise.

If you have a good multimeter that can measure true rms AC with audio frequency bandwidth, you could measure the AC voltage of hiss at the output and we can see if it seems excessive or not. If your multimeter has a low pass filter, ensure it is disabled. For a comparison, my CJ ET5 preamp with a very old tube that has just under 10,000 hours on it, with the volume at about the middle setting, has these measurements:
at volume setting 1 (lowest): 0.08mv AC
at volume setting 44 (a typical setting for me): about 0.9mV AC
at volume setting 50 (middle): about 1.5mV AC
at volume setting 99 (highest): about 7mV AC

In my system it is still very low noise except at very high volume settings which I never use for listening. My speakers are very inefficient though and are in a big room with a moderate gain power amp. I would think if yours measures 2mv AC or less with a suitable multimeter, then your preamp is probably normal.

Regarding the "capasitors in the line section have a bigger value than the part list says. It should be 2 uF, but it is 4 uF. Is that a problem?" Short answer - not a problem. Perhaps you are reading the wrong schematic and parts list? The one for pv10a (related to pv10al) that I have has no 2uF listed. It has a few 4mF (4uF) 400V listed. In any case in the position they are in, at least for C19 on the schematic, I think they are just used as dc blocking capacitors so 2uF would be good, 4uF would be better allowing bass frequencies to reach slightly lower. Not a big difference either way though.

From looking at your post on hifisentralen.no you seem to be using the pv10 parts list rather than the pv10a. Get the pv10a ones from the schematic section of conradjohnsonowners.com.

note: I am not an electronics engineer so some of my interpretation may be wrong.

[roberto]

I have e Conrad Johnson PV10AL. The one with three knobs in the front.
I have recently changed the tube sockets and tubes because of some squeaking noise problems. And it got way better. But I still have some noise. Its a hissing noise I can hear all the way to listening position when the music stops. Its an constant level, no difference when i turn the volume knob. Do you think it about time to do some capasitor changes? And which capasitors to change?
Can there be an issue that there are now earth/ground wire on this?
I have the parts list and the schema, and it looks like the capasitors in the line section have a bigger value than the part list says. It should be 2 uF, but it is 4 uF. Is that a problem?

All those brown color burned resistors should be changed too. There could be your noise. The value of the resistors due to their high temperature (brown burned color) suggested that they could be out of value too. Take it to a good technician and tell him to change those resistors. There could be your hissing problem too.

Happy listening!