White noise from CAV 50

[teb76]

Perhaps a fool question, stated that this is my first tube amp: when I have no signal at the input I hear a kind of white noise from the speakers, even at low volume. Is this normal? If not, what should I check?
Thank you.

[admin]

No, not normal.

Many things can cause noise. Couple of questions to help narrow down the problem:

1) Does the volume of noise change with the volume setting of the CAV50?
2) Is it really white noise, or a noise at exactly 60 hz?
3) Does the noise change if you manually move any power cords away from the interconnects?
4) Is the noise equal volume in both channels?
5) Does the noise change at all with dampening of the tubes (ie touching the tube ideally with a non-conductive item, but your hand, to dampen any potential vibration)?

[teb76]

No, not normal.

Many things can cause noise. Couple of questions to help narrow down the problem:

1) Does the volume of noise change with the volume setting of the CAV50?
2) Is it really white noise, or a noise at exactly 60 hz?
3) Does the noise change if you manually move any power cords away from the interconnects?
4) Is the noise equal volume in both channels?
5) Does the noise change at all with dampening of the tubes (ie touching the tube ideally with a non-conductive item, but your hand, to dampen any potential vibration)?

Thanks for answering!

1) Yes

2) Here is the spectrum, you are right, it' clearly coming from power suppy (in Italy 50 Hz) with a huge peak at 100 Hz, there's a floor but the clear peaks.

Screenshot_20221009-131238_Spectroid.jpg

3) It changes touching the input selector and the volume knob as well, no change toching other (cables, valve, ...). It's louder when the selector is an open (not used/connect) input, far better when in connected input.

4) looks louder on the right channel

5) no

[admin]

If it's 50hz or a multiple, it may be a ground loop.

The variance between the two channels concerns me about something more significant.

I like to start off with the low hanging fruit (ground loop). If you have a ground loop isolator RCA connector, put that between the denon and the CAV50. If not, turn everything off. Disconnect the denon from the CAV50 (so there are no other component connections than the CAV50 to the speaker), and use another source (like your phone connected via 3.5mm plug to RCA) and see if the noise goes away or changes.

[AnotherJohnson]

It’s probably one of the small driver tubes, and/or cable routing, and possibly some RFI.

Try reseating the tubes and the interconnects.
Don’t turn it on and off and on and off. Give the caps a chance to settle down ( a couple minutes) before any restarts.

[AnotherJohnson]

Unplug sources. Does it go away? If it’s a ground loop, it should drop out when the offending component is removed. But the cable routing, small tube, or filter caps are my guess.

Kevin Deal would ask “Why are you listening to NO PROGRAM?” “Stop worrying about how it sounds when there’s no music. Tubes make some noise. You don’t hear it when the program is playing. Forget about it.”

Hiss is not hum. Hum is clearly a primary frequency. You’ve got lots of frequency content.

Since you called it “like white noise”, which is hiss, at the start, my money is on small driver tube noise.

[teb76]

Everything disconnect and unplugged noise remain the same. Yes your right, at first it was a kind of white noise, actually it is not, as shown.
Should I try crossing valves or change it? Don't know...

[teb76]

Everything disconnect and unplugged noise remain the same. Yes your right, at first it was a kind of white noise, actually it is not, as shown.
Should I try crossing valves or change it? Don't know...

At volume higher than 30% I hear a click from the speakers when rotating the input selector

[admin]

You can try switching the tubes to see if that has any results. If so, then it narrows it down to a tube issue. Note, you may have to rebias.

The clicking may be from the actual volume control. Sometimes you get some oxidation there. A little deoxit spray and some vigorous turning up and down can fix that (all with the unit off and unplugged).

[AnotherJohnson]

It’s not likely to be a power tube, so don’t worry about rebiasing. It is a classic small driver tube issue.

[AnotherJohnson]

Replacement Tube Set RCAV50
12AU7 | 2 12AX7 | 2 6SN7 | 4 EL34

It’s likely to be one of the 12A?7 tubes. Start there. It could be a socket too, but R&R each tube should clean pins.

[admin]

I agree with AJ. If it's a tube issue, most likely not going to be a power tube. I would reseat all the tubes as it's low hanging fruit.

[AnotherJohnson]

Those 6xxx tubes are drivers too.

[teb76]

Thank you, I'll try also cleaning the socket with some contact cleaner and let you know.

[AnotherJohnson]

Contact cleaner is generally not recommended for cleaning pins or sockets.

[teb76]

Contact cleaner is generally not recommended for cleaning pins or sockets.

Good to know... I was going to use it... What can I use instead?

[AnotherJohnson]

The friction of r&r is enough. If you’ve got real corrosion, replace the socket.