The DBRB | dual bridge rectifier board

[scottjoplin]

The amps I built don't have an option for the hum loop breaking resistor between signal ground and power ground, I could implement it by modifying the PCBs, but at present I've just added one 10 ohm resistor in series with the input ground of one channel. What are the down sides of this?

 

[jwilhelm]

This depends on the actual amplifier. The source side of the 10R resistor would be a cleaner ground reference. If the amplifier uses a DC servo the cleaner side of the ground reference is the ideal place for the servo to connect. Feedback reference should also connect there.

 

[scottjoplin]

I understand that, however as I said, at the moment it is only on the input ground of one channel, that is, between the shield and input return, to combat cross channel ground loop, which it does, although, not perfectly I admit. I am wondering what is the down side?

 

[jwilhelm]

There would possibly be increased distortion in the channel with the 10R resistor in series, but it would much less audible than any ground loop. The shield of the input is no longer at the same potential as the input reference of the amplifier (antenna), but at 10R separating them I doubt this is an issue. There should likely be high current diodes connected in parallel with the 10R resistor for safety from shock on the shield though.

 

[scottjoplin]

Thanks, that's what I suspected. The shields are connected at the source (the cause of the loop) and to earth at this point so safety isn't an issue.

 

[jwilhelm]

Are the shields connected directly to earth ground? That's not ideal.

 

[scottjoplin]

I don't know, it's inside a Behringer DSP