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In Reply to: RE: Scott 130 preamp buzzing on one channel posted by Michael Samra on July 26, 2017 at 13:48:29
buzz, the final cap for the heater supply was grounded to the ground of the B channel ground, moving this to the star ground point eliminated the buzz. Does raise a question, Michael. how is the grounding arrangement for the filament DC supply done? Where is the bridge rectifier grounded as well as the caps for the filament DC supply, together and then to the star ground? I see the hum control is center tapped to the negative of the rectifier. Thanks!
Follow Ups:
The fil supply grounds to the center tap of the HV transformer. In other words, ground the bridge for the fil supply to the hv CT. Scott schematics are confusing on their grounds.They did kind of a sloppy job of differentiating the grounds.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 07/27/17
Thanks, Michael, should I ground all of the grounds for the filament supply to the HV CT? In other words, the cap grounds and the filament return grounds? Or just the bridge to ground and the ground the caps to the filament return grounds and then to the star ground? Thanks, Randy
I would, yes. If there If a problem arises, we can change it.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
I grounded the filament supply caps, the filament string ground, and the bridge rectifier to one of the B+ power supply cap ground that daisy chains to the star ground, at this point there is a little buzz with the volume turned all the way up, at normal listening volume there is almost nothing at the speaker, very quiet! Connected to my newly restored W4-AMs (with Dave G. mods) the sound is very transparent and clean, thanks for all you help. If you think the DC filament supply should all go to the star ground, let me know, I saw in one pic that there is a pair of 1 watt resistors connected between the two can ground lugs, those cans have both the filament supply caps and the B+ supply caps, do you know what the resistors are for? They don't show up on the schematic. Thanks, Randy
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