Strange slight hum + noise issue

[rhythmsandy]

Im getting a strange noise after using the amp for about 6 months. The problem is

channel 1: rca signal input is connected and no noise+hum coming out of it.
channel 2: rca signal input is connected and now the noise appears on both the channels and the strange part is its vice versa.

If one channel is connected then no noise and if both are connected then the noise appears.

connected the chassis to the ground but still the hum persists. No idea why this is happening any thing might have gone wrong?

 

[Ian Finch]

You know, it would help if you said what you are talking about.
What is "the amp" and what is your source. It should be clear so far that there is a common
link such as the grounding of the source output, which has probably changed in 6 months.

 

[RJM1]

It sounds like you have a voltage difference between the ground connections on the two RCA input connectors either on the input cables or in the amplifier. When you connect the two grounds together a current flows in the grounds and causes a hum. If you run an RCA cable between both input connectors on the amp and have no hum, measure the voltage ( AC and DC ) between the grounds on your input cables.

 

[rhythmsandy]

I did the measurement on two cases

1. 0mV when no inputs were connected to the amp
2. .2mV to .6mV when one input is connected and that value is fluctuating.

But how do I solve it?

This problem arised when i changed the internal wiring for the input signal with a Reference Microphone cable. I was using sommer before but now I have changed to Reference Microphone cable and the problem arised. You want me to roll back to older ones? but atleast should know what went wrong... where to look at now?

 

[AndrewT]

0mV .2mV .6mV

What are these?

AC or DC?
Low frequency or High frequency?

If AC, then the readings you post should look like this:
0mVac, 0.2mVac, 0.6mVac

If DC, then the readings you post should look like this:
0mVdc, 0.2mVdc, 0.6mVdc

Which?

when no inputs were connected

Is that open circuit input, or shorted input?

when one input is connected

Connected to what?

 

[rhythmsandy]

What are these?

AC or DC?
Low frequency or High frequency?

If AC, then the readings you post should look like this:
0mVac, 0.2mVac, 0.6mVac

If DC, then the readings you post should look like this:
0mVdc, 0.2mVdc, 0.6mVdc

Which?Is that open circuit input, or shorted input?Connected to what?

These are Vdc readings.
On AC readings the observed value is 0

These are connected to the JDS lab ODAC.

These are open circuit input.