Amp hum increases and decreases

[Joe Appierto]

If the cheater plug works, then you know that's the issue. Have you by any chance recently hooked up your cable service to your stereo system? I know I had to get one of those isolation transformers and hook it up to the cable lead before the hum went away in my system.

As I remember, even with the isolation transformer, the system hummed with both the Pr. 11A and the 140 unless I used a cheater plug.

[pstrisik]

Ha! Cheater plug worked. I didn't have time last night and gave it a quick try this morning, so I don't know more. My repaired mono amp will be picked up tomorrow, so I'll first see if there is a hum problem with them. If not, I'll be good. If so, I'll try to track down the ground problem more rather than depend on the cheaters.

Though it sounds like ground lift is acceptable practice. Some components have a lift switch even. Any cautions?

[ronenash]

Disconnecting the ground on tube components that have over 500 volts inside is not a good practice. Organizing your cables in a clean way usually solves he problem.

[pstrisik]

I'm doing my best!

If it is cables, it would seem that moving cables (while still connected) one by one should produce some variance in the hum but it doesn't.

[ronenash]

Try disconnecting the sources from you preamp one by one to see if you can get rid of the hum. It is usually coming from one of the sources. Its a tedious job to nail down hum problems but floating ground in a tube amp is not the solution imho. The risk is just too high.
I have done this in my system and the end result is that I have all amps and preamps Connected to one power distribution box (Wireworld Matrix), all digital sources and PC Connected to another distribution box and my analog sources and their marching phono stages Connected to a third distribution box. All distribution boxes are connected to a Torus power conditioner. This setup resulted in zero hum and noise.

I hope this will help out.

[klipschfan]

UNDERSTANDING, FINDING,
& ELIMINATING GROUND LOOPS
IN AUDIO & VIDEO SYSTEMS
http://www.jensen-transformers.com/a...%20seminar.pdf

[pstrisik]

Originally Posted by ronenash

Try disconnecting the sources from you preamp one by one to see if you can get rid of the hum. It is usually coming from one of the sources. Its a tedious job to nail down hum problems but floating ground in a tube amp is not the solution imho. The risk is just too high.
I have done this in my system and the end result is that I have all amps and preamps Connected to one power distribution box (Wireworld Matrix), all digital sources and PC Connected to another distribution box and my analog sources and their marching phono stages Connected to a third distribution box. All distribution boxes are connected to a Torus power conditioner. This setup resulted in zero hum and noise.

I hope this will help out.

Thanks Ron. It's all helpful.

Disconnecting sources from the preamp likely won't help as I have tried with the preamp disconnect from the amp. It seems like it is something about what is plugged into the wall. I will try the one by one method with things unplugged then plugging them in one by one. Hopefully the hum will disappear with most everything unplugged except the amp.

With your system it seems like everything is ultimately plugged into the same circuit. If true, it must be something about the power conditioning that is eliminating your ground issue.

[pstrisik]

Originally Posted by klipschfan

UNDERSTANDING, FINDING,
& ELIMINATING GROUND LOOPS
IN AUDIO & VIDEO SYSTEMS
http://www.jensen-transformers.com/a...%20seminar.pdf

Thanks for this! I will dig in and see what I can learn.

[pstrisik]

Sorry, Ray. It looks like I did take over your thread! How's your transformer hum situation?

[rlw3]

No worries, my lp 275s are quiet in the mornings but get noisy by 5-6 pm. Dont know if this is a heat build up issue or the power out of the wall getting dirty as the day goes on. If noise growth remains during cooler weather this fall then i would have to think it is a heat build up problem. Peter i assume you tried using the 3 prong wall socket testing device and all was good?