• 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.

Grounding scheme

Status
Not open for further replies.
Jump to Latest
#3
Star grounding is a very good idea. But you also want to make sure that you don't create any (geometric) area between conductor pairs, such as each signal input conductor and its ground conductor. [Otherwise, a time-varying (e.g. AC) magnetic field will induce a current in the loop they form, which, in the case of an input pair, will induce a voltage across the grid input resistor whenever an input device is connected or the input is shorted.] Each input signal/ground conductor pair should be tightly twisted together, all the way from the input jack to the grid resistor, and preferably should be inside a shielded cable, with the shield grounded to the chassis at one end only (the input end).

The same idea goes for all other conductor pairs inside the amp, including AC pairs, DC power/ground pairs, output signal/ground, etc, although just tightly twisting each pair together is usually good enough, for those.

Also, keep all low-level signal conductors away from everything else, if possible, especially high-power and AC conductors and devices. And keep everything away from the AC, if possible.

Cheers,

Tom Gootee
 
Last edited:
#4
For my modified stereo 5-10 amp I used two ground busbars. One for the input and phase splitter stages, the other for the output cathodes. The two were joined at a star point, where the PSU ground joined them. HT (B+) decoupling capacitors for each stage were grounded on the busbar near the stage. The aim was to avoid loops, and to keep output stage currents well away from the input stages. Also, keep PSU charging pulses well away from everything. I did not bother to keep the two channels separate, as they have to be joined at the input and PSU anyway and I did not want to introduce a loop so both inputs were grounded together to the input stage busbar.

For safety the chassis was connected to mains ground. The signal star point was connected to the chassis via a big 10ohm wirewound resistor. This is big enough to reduce hum loops, but small enough to blow a fuse if there is a short.
 
Status
Not open for further replies.
Top Bottom