Noise troubleshooting

[jimbones]

getting warmer, err closer to finding the culprit. I believe it is the tube in my ET5!! One channel is hissy. Lol. OK that was a brand new Gold Lion that lasted a year (Maybe 500 hours on it)

[admin]

Tube life is always a little bit of a tossup. I've had some tubes last for a decade of use and others fail within months. At the end of the day, a tube replacement is still going to be the easiest/cheapest "fix".

[jimbones]

OK so here is the final fix, a bit complicated and I have absolutely no idea why it has to be so complicated but here it is.

One amp plugged into a duplex on circuit A (with Gnd)
One amp plugged into another duplex on circuit B (Gnd lifted)
Replaced Preamp tube one channel hissy.

The bad tube was a Gold Lion with only about 500 hours on it. I had a spare Siemens tube. Although it came with my pre I dont know how many hours are on it but it has better SQ than the GL. I will call Brent Jessee to get another 6922 per his recommendation.

[admin]

I'm glad the noise is gone but I am a little concerned about the ground being lifted on one of the amps. If grounding has an audible result, it's typically a ground loop issue. That should be a 60 hz hum.

Have you tried having both the amps on the same circuit? Or even all the stereo equipment on the same circuit? For diagnostic purposes I would even throw a ground loop isolate in there to see if that has an effect as that is a sure way to diagnose a ground loop in my experience.

[jimbones]

I'm glad the noise is gone but I am a little concerned about the ground being lifted on one of the amps. If grounding has an audible result, it's typically a ground loop issue. That should be a 60 hz hum.

Have you tried having both the amps on the same circuit? Or even all the stereo equipment on the same circuit? For diagnostic purposes I would even throw a ground loop isolate in there to see if that has an effect as that is a sure way to diagnose a ground loop in my experience.

It was a buzz (about 480 hz) a multiple of 60 hz and I did try it on the same duplex. NG. The Isolator: Is that the RCA ground loop isolator?

[admin]

Yes, a RCA ground loop isolator would be something I would test the system with to see if it is some way related to ground loop vs an internal issue.

Something like this: https://www.amazon.com/Conext-Link-Chan ... 138&sr=8-5

[roberto]

To make sure from where the hum is coming, I suggest to disconnect the RCA cable from the input of the amplifier y turn it on. Is there hum?, No?, might be the RCA cable or from the preamp to the amp. Still noise? So disconnect the inputs in the preamp a leave only a connection from the output of the preamp to the input of the amplifiers and turn them on. Do you have hum? Yes? The preamp is the cultprit, NO? it is coming from the TV cable box. Disconnect the cable box Antenna or coax tv cable from the TV box. NO hum?, then you need an antenna coax noise suppressor.

Please tell us your findings. Usually that ugly noise is a bad RCA cable.

[artoly]

I hope you get it sorted jimbones.
You and others in this thread will know a lot more than I do about ground loops, but I had one. I was a bit nervous about lifters (I imagine that an understanding about alternative earth paths, would make them less risky). Eventually ended up with an Ifi GND Defender on my Premier 350 (actually on a mains block, because the 350 does not have the same plug type as the Ifi). I tried lots of RCA and power cable swapping beforehand, and then tried the Ifi in front of every box, but putting it on the 350 was the only place that made the noise go away. It worked, so it stayed. Hopefully they are as safe as they purport.

[jimbones]

I looked up the Ifi product. It looks like a ground lift product at the IEC end of the cable... I dont know how it is different from a cheater

[admin]

I suggest to disconnect the RCA cable from the input of the amplifier y turn it on.

Roberto,
I've heard some people say that tube amps should always have a RCA connected (to preamp) when turning them on (and to not turn it on unconnected). I don't know if there is any true concern?

I looked up the Ifi product. It looks like a ground lift product at the IEC end of the cable... I dont know how it is different from a cheater

It would be the same I suppose. The ground connection is interrupted so not sure what difference it makes on what side of the cable that is done?

[roberto]

That's not right. You can do it without any problem. I have being servicing a lot of different brands over more than 50 years and the truth is, there is no reason why you should not do it. When turning the tube amp off, you must wait at least 1 minute before you reconnect something. Tubes are still on when there is no AC...transistors usually in 5 to 10 seconds are totally off.

[roberto]

If you are trying to find a problem, the only way is turning the unit on without any connection. If you want to play safe, make a short to the RCA cable, and there will be no problem. Shorting the cable will prevent any odd noise or a possible oscillation. We are talking CJ here. If the amp is bad, it might oscillate...but I never, never had a CJ power amp with an oscillation because to turn it on without any cable. If a possible oscillation might occur, there must be a warning in the operation manual about this, right? My advice is: treat you goods with respect and don't do anything that could harm the amp or the speakers. If you have caution doing all the tests, you can isolate faster the problem.

[admin]

That's not right. You can do it without any problem. I have being servicing a lot of different brands over more than 50 years and the truth is, there is no reason why you should not do it. When turning the tube amp off, you must wait at least 1 minute before you reconnect something. Tubes are still on when there is no AC...transistors usually in 5 to 10 seconds are totally off.

I think you are right about this. I can't remember where I read this but it was probably on some other audio forum. For those reading, I would disregard my statements about not turning on an amp without input connectors.

[roberto]

Even a little bit more about playing safe on tubes...they should not be turned on without any load. I use a big 4 ohms resistors...not speakers while I am servicing them. The transformers must have at least a phantom load. But for a minute or so, it is safe, specially without any input voltage. if you have a cd player or a preamp connected to the input of the amp and there is no phantom load or speakers, you could burn the output transformers. The transformers need to release that energy through the phantom load or the speakers. These might me what you read dear Admin...this is a true thing and we must have caution with it.

[roberto]

Dummy load = phantom load. The right name is dummy load. Also is good to have another very important tool on hand: A Variac transformer with Amp meter.

Happy listen to all.