• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

signal ground and earth ground

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi frank2395,
We use a resistance to reduce circulating ground currents. A direct connection would tend to encourage this.
The currents we are concerned about can flow through the sheilds of the connecting audio cords and back through the chassis and ground pin on the power cord back to the offending equipment. Could even be as simple as a different phase of power off the breaker (fuse) panel.
These currents can become very high (destructive). I'd rather burn out a resistor rather than PCB traces. This may possibly destroy components. Close lightning strikes are my favorite example of this. There is no real protection against this.

-Chris
 

EC8010

diyAudio Moderator Emeritus
2003-01-18 7:57 am
Near London. UK
ttray321 said:
If I use this circuit, I may try only one diode.

No, for safety you must use two diodes back to back in parallel, and high current ones at that. A cheap convenient source of high current diodes is a 35A bridge rectifier...

Incidentally, I believe the diagram in the earlier post has an error in it; the lower AC terminal of the bridge rectifier should connect to the same point as the upper AC terminal (ie, the negative side of the upper DC supply).
 

anatech

Administrator
Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi ttray321,
The capacitor is for RF frequencies. Depending on what is earthed and what is at circuit ground. The value will be different depending on who designed and built the object in question. Try different values as these are ballpark anyhow.
I normally earth the chassis for safety and RF shielding, hence the lack of C for me. Then there is no safety issue when the resistor burns out.
-Chris
 
EC8010 said:


No, for safety you must use two diodes back to back in parallel, and high current ones at that. A cheap convenient source of high current diodes is a 35A bridge rectifier...

Incidentally, I believe the diagram in the earlier post has an error in it; the lower AC terminal of the bridge rectifier should connect to the same point as the upper AC terminal (ie, the negative side of the upper DC supply).

I truncated that diagragm, but maybe not enough. The only part that's really relavent is the bridge rectifier connected to the AC/Mains ground.
The bridge will not pass signal ground loop current ( no loop hum), but will conduct over a few volts and serve as a safety ground.

A 35A bridge rectifier is just fine.

;)