I have a few questions.
If your amp did not hum at the techs shop then it's not the amp.
1. Is your amp in a rack or free standing on the floor.
( if in a rack take it out of the rack / unplug everything except the speakers )
2. You lifted ground, how did you do that . Switch on the amp or removing the ground leg off of the power cord. You need to lift the electrical ground of the power cable to the amp.Using a 3 to 2 adapter does the trick put you have to pull off any metal loop that would touch the center screw that holds the wall plate on the wall outlet plug.
Take your power DODD transformer out,plug straight into wall jack.
3. Have you tried other speakers to make sure it's not your speakers crossovers.
If the ground is till there then it's the amp for sure.
If you are clean then plug in the Preamp with nothing in the input section,turn it on. ( do not put the frame of the preamp in contact with the amp frame ).
4. LED lights of any kind on the audio AC wall socket all the way to the circuit breakers ( notoriously buzzy and it goes down the ground leg)
Same applies to dimmers of any kind.
5. If you put a meter on your AC wall jack ,what is the reading between the + leg to ground ( should be 120V ac ) then - to ground ( that should be 0 ac volts ).
If you have dimmers on that AC line turn them low to midway and then check your ground voltage again.If it goes higher than previous test with them off you might have found your problem.Even completely off LED light circuits still burn power that is leaked by the dimmers ( hence LED light glow when in the off position )
It makes no sense that the amp is quiet with another system and installed in your set up it starts buzzing.
Anyhow a lot of good thoughts in the upper threads but there is no mention on how your systems is installed in the room ( rack or no rack ) Components touching other components. I fight those issues daily with amp racks more so in permanent installation steel frames and rails.
Good luck.
If your amp did not hum at the techs shop then it's not the amp.
1. Is your amp in a rack or free standing on the floor.
( if in a rack take it out of the rack / unplug everything except the speakers )
2. You lifted ground, how did you do that . Switch on the amp or removing the ground leg off of the power cord. You need to lift the electrical ground of the power cable to the amp.Using a 3 to 2 adapter does the trick put you have to pull off any metal loop that would touch the center screw that holds the wall plate on the wall outlet plug.
Take your power DODD transformer out,plug straight into wall jack.
3. Have you tried other speakers to make sure it's not your speakers crossovers.
If the ground is till there then it's the amp for sure.
If you are clean then plug in the Preamp with nothing in the input section,turn it on. ( do not put the frame of the preamp in contact with the amp frame ).
4. LED lights of any kind on the audio AC wall socket all the way to the circuit breakers ( notoriously buzzy and it goes down the ground leg)
Same applies to dimmers of any kind.
5. If you put a meter on your AC wall jack ,what is the reading between the + leg to ground ( should be 120V ac ) then - to ground ( that should be 0 ac volts ).
If you have dimmers on that AC line turn them low to midway and then check your ground voltage again.If it goes higher than previous test with them off you might have found your problem.Even completely off LED light circuits still burn power that is leaked by the dimmers ( hence LED light glow when in the off position )
It makes no sense that the amp is quiet with another system and installed in your set up it starts buzzing.
Anyhow a lot of good thoughts in the upper threads but there is no mention on how your systems is installed in the room ( rack or no rack ) Components touching other components. I fight those issues daily with amp racks more so in permanent installation steel frames and rails.
Good luck.