Adcom GTP 400

[rodrigosalvati]

Hello,

I am trying to repair an Adcom GTP400 preamp for and intermittent whining noise, but now I and am getting a loud ground loop when connecting to certain equipment.

My first question is:
Should the preamp outputs rca ground shell be grounded to the chassis and ground in the PCB?

The inputs are all grounded, but the out is not.

Thanks,
Rodrigo

 

[rayma]

All RCA ground shells are connected to audio ground in some way, through the boards and connectors.
It's best to check with an ohm meter. They are also connected to the chassis by a single connection
between the audio ground and the chassis ground.
Adcom GTP-400 - Manual - Tuner / Pre-Amplifier - HiFi Engine

 

[rodrigosalvati]

Thanks. It seems the RCA connector has a problem as there is no continuity between the shell and the pin. There is continuity between chassis ground and the hole on the PCB where the ground of the connector is soldered to.

 

[rayma]

There is normally a high resistance (10k-100k) between the RCA shell and the RCA center pin.
You have to use a high resistance range on the meter for that, not the diode function.

 

[rodrigosalvati]

Problem solved. I ran the red wire to ground.
Thanks