Pc2002m ground switch

[70barracuda]

Getting some hum through my speakers, and in the Yamaha instructions for the pc2002m it says you can turn off the ground switch on the back to eliminate the hum. Before I do, is there any issues it would cause? I'm running a pre amp into dual mono pc2002m using the xlr connections.

 

[mbz]

Does not appear to be any safety issue. The switch simply "breaks" the connection between in the input/xlr GND pin and the amp chassis GND.
So try it and report back. If hum still present then determine hum frequency, either 50/60Hz mains hum or rectified 100/120Hz. Mobile phone ap like spectroid or ... or you can record and upload into freeware audacity or ... May help to localize cause.

 

[70barracuda]

So turned the amps on with the switches off and got a super loud hum. Turned off immediately and put switches back to on. Still a low hum. Used the app mention and it's a 120hz sound.

Weird thing is it's only when the second amp is turned on. Doesn't matter which one, once the second is turned on the hum starts.

 

[avionic]

Doesn't matter which one, once the second is turned on the hum starts

Both channels .. ?

 

[70barracuda]

Yup

 

[avionic]

dual mono pc2002m using the xlr connections.

There is only one power transformer.. So technically it is not a dual mono..

 

[70barracuda]

There is only one power transformer.. So technically it is not a dual mono..

I'm running two pc2002m's in mono. Probably worded it wrong.

 

[avionic]

Oh ! ..Nevermind..

How about running the power amps on two separate AC circuits ?

 

[avionic]

Any noisy electronics nearby ? Dimmer switches ?

 

[70barracuda]

Oh..Nevermind.. How about running the power amps on two separate AC circuits ?

Can't try that right now but I will be adding a separate breaker and outlet just for my system so I can try one on each once it's all done.

Fish tank with heater, filters, air pump etc on the same circuit...

 

[avionic]

Can't try that right now but I will be adding a separate breaker and outlet just for my system so I can try one on each once it's all done.

Fish tank with heater, filters, air pump etc on the same circuit...

Possibilities ..

 

[avionic]

Did either amplifier have input power issues or modifications ?

 

[70barracuda]

Did either amplifier have input power issues or modifications ?

Not that I know off. They both are pretty clean and stock looking inside. I've only cleaned switches and attenuators.

 

[avionic]

Did you have them plugged into the same receptacle ?

 

[Sparkplug]

You get the hum with inputs (xlr) connected or without? If you’re on xlr getting the hum, try unbalanced inputs or no inputs to see what happens …

 

[mbz]

Still a low hum. Used the app mention and it's a 120hz sound.

Suggests after rectification???

Weird thing is it's only when the second amp is turned on. Doesn't matter which one, once the second is turned on the hum starts.

A bit of a reach but could it be that the GND from PC(1) is significantly different to PC(2) and GND loop by xlr's back to pre?

Turn off that GND switch on any one(only) PC amp and retest.

What pre are you using?

 

[70barracuda]

Pre amp is a Yamaha c-80. And it still makes the hum with the inputs disconnected on the amp.