joulupukki
Tele-Holic
In my quest to remove as much self-noise as possible from my single-channel AB763 build(s) (I'm gearing up to build v2) I've been studying different layouts. There are some interesting things going on in the Fender '64 Custom Deluxe Reverb Hand Wired amp (have only seen pictures, no schematics or diagrams) – like that it seems V1B and V2B uses a shared cathode?
I think, after making some good grounding discoveries in my v1 build, that I'm a bit more sensitive to what I want to try in the v2 build. I was looking through the Hoffman 1-Channel AB763 layout diagram (https://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf) and realized that the Phase Inverter is grounded with the power transformer ground lug and not the preamp through the negative feedback tail resistor. Mine is currently grounded with the preamp bus (which grounds to the chassis at the input jack).
Through some re-routing of local ground wires (to ground at the same point on the bus wire as the cathodes for a particular stage) I've been able to greatly reduce hum and buzz in my first build. I still would like to experiment with this (moving the PI NFB's tail resistor) to the output transformer ground to see if there's any difference.
Also, with all the other good fixes in my build, I'd like to remove the power transformer ground entirely and tie into the main preamp bus to see if there's less hum. I tried this earlier and it didn't really seem to help much, but that was before I made the other local circuit ground improvements.
But ... I wondered if any of you have had experience positive/negative using one way or the other with the NFB tail ground location in an AB763-style amp?
I think, after making some good grounding discoveries in my v1 build, that I'm a bit more sensitive to what I want to try in the v2 build. I was looking through the Hoffman 1-Channel AB763 layout diagram (https://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf) and realized that the Phase Inverter is grounded with the power transformer ground lug and not the preamp through the negative feedback tail resistor. Mine is currently grounded with the preamp bus (which grounds to the chassis at the input jack).
Through some re-routing of local ground wires (to ground at the same point on the bus wire as the cathodes for a particular stage) I've been able to greatly reduce hum and buzz in my first build. I still would like to experiment with this (moving the PI NFB's tail resistor) to the output transformer ground to see if there's any difference.
Also, with all the other good fixes in my build, I'd like to remove the power transformer ground entirely and tie into the main preamp bus to see if there's less hum. I tried this earlier and it didn't really seem to help much, but that was before I made the other local circuit ground improvements.
But ... I wondered if any of you have had experience positive/negative using one way or the other with the NFB tail ground location in an AB763-style amp?
