help finding 115/230 primary to 12v secondary relay tranny

[martin manning]

You didn't say you had a 5VAC winding available. I'd use that for sure, with a FWB rectifier and 5V relays, or a voltage doubler to get 9V regulated using 9V relays. Then you could have power for a pedal available from your foot switch.

[Tonegeek]

You didn't say you had a 5VAC winding available. I'd use that for sure, with a FWB rectifier and 5V relays, or a voltage doubler to get 9V regulated using 9V relays. Then you could have power for a pedal available from your foot switch.

I don't have a 5v tap but that tranny is an option although kind of overkill and expensive. My amps use 12v relays but in a pinch I could build a tripler.

[martin manning]

In that case I'd be inclined to put a FW voltage doubler on the filament winding and regulate it to 12V. This would end up elevating the filament string half-way to the regulator input voltage, maybe 8V or so.

[Tonegeek]

In that case I'd be inclined to put a FW voltage doubler on the filament winding and regulate it to 12V. This would end up elevating the filament string half-way to the regulator input voltage, maybe 8V or so.

Not sure I am following you. The FW doubler is the circuit I had the hum with.

[martin manning]

I think using the filament supply will be hum-free if you use the standard CT ground or 2x 100R artificial CT, and keep the doubler and relay coil circuit isolated from chassis ground. You don't really need the regulator, which would make isolation easier.

[Tonegeek]

I think using the filament supply will be hum-free if you use the standard CT ground or 2x 100R artificial CT, and keep the doubler and relay coil circuit isolated from chassis ground. You don't really need the regulator, which would make isolation easier.

Attached is the circuit I had before that caused some hum in a 2 relay system (only on one relay - PAB). I wonder if it would be quieter using the 100R resistors instead of the center tap. I did try more filtering to no avail. I think the diode switching is bleeding in somewhere. OOPS, drawing should have 0 volts instead of -12V.

[martin manning]

Did you ground the relay supply, i.e. the 0V?

[Tonegeek]

Did you ground the relay supply, i.e. the 0V?

I can't remember, but doubt it.

[martin manning]

You would want to ground it at only one place, either at the CT (vrai ou faux) or the 0v DC. I don't see why either way wouldn't work, and if the DC is the ground reference the filament string average would be elevated to half the DC voltage plus half the peak AC. Maybe just have to try it and see?

[Tonegeek]

You would want to ground it at only one place, either at the CT (vrai ou faux) or the 0v DC. I don't see why either way wouldn't work, and if the DC is the ground reference the filament string average would be elevated to half the DC voltage plus half the peak AC. Maybe just have to try it and see?

I think I tried the CT but don't remember so I will try it again. If that hums, I will lift the ct and add 2 100k resistors and tie D8 to Gnd. like the MK 4: (Is this what you mean, or did I miss something?) Really I think I have tried everything but using the ground reference resistors but it is not too hard to try it all again. I did read somewhere that some prefer the 100R resistors over the CT. It may be a few days before I get to it.

[Tonegeek]

Decided to make time to work on this after all. I just tried the exact circuit from my last post(using the 100R resistors, no center tap). It hums enough to be an issue at high volume. I also tried with the 6.3V center tap on, no resistors. You can't ground the low side of the DC relay supply to the main bus this way as it will short through the diodes back to the hot legs of the the filament winding. So leaving the DC floating it was quieter than the way Boogie does it. This way is useable, but barely. However it is still not as quiet as using a separate transformer. I put the transformer supply back and it was quiet as a mouse. BTW on this arrangement I did connect the low DC side to the main bus as it does hum unless you do. I sure did hope the filament winding would do it for me.

[martin manning]

Thanks for the report. I was surprised to see both the CT (2x 100R) and the DC grounded in the schematic you posted. Did you happen to try grounding the DC side only?

[Tonegeek]

Thanks for the report. I was surprised to see both the CT (2x 100R) and the DC grounded in the schematic you posted. Did you happen to try grounding the DC side only?

U referring to the MK 4 schematic? Yes I tried it exactly like the schematic and without the 100R resistors. No difference. I wonder if bypassing the doubler diodes with small caps would help? Guess I will try that and see. Heck that MK 4 schematic could be wrong although it looks ok to me. Like you said, it should work, but it hums just enough to be an issue.