I finished building 5F1 champ amplifier, but I get horrible hum 🙁
It is very loud, almost as loud as the amplified guitar signal.
Also, volume pot affects it (at minimum gain I hear almost no buzz). Connecting jack into input 2 has no effect on hum, but on the first input it makes it even worse.
I suspect it has something to do with preamp section, and input jacks/grounding.
I tried different grounding layouts I found on the internet, and also changing the preamp tube, but nothing seems to fix the problem.
(I also noticed HT has 400V instead of 340, which is just within tolerance, but you never know)
Current grounding:
Safety earth has it's own lug.
Second lug separate wires (power transformer CT) - (reservoir cap/first filter cap) - (second filter cap and the rest of the audio circuit ) - (volume knob) - (preamp tube bias resistor)
Non insulating output and input jacks are directly grounded to chassis (just using the mount, not wiring). I know it's probably not a good idea, but a lot of vintage amps get away with it.
Any advice would be appreciated.
It is very loud, almost as loud as the amplified guitar signal.
Also, volume pot affects it (at minimum gain I hear almost no buzz). Connecting jack into input 2 has no effect on hum, but on the first input it makes it even worse.
I suspect it has something to do with preamp section, and input jacks/grounding.
I tried different grounding layouts I found on the internet, and also changing the preamp tube, but nothing seems to fix the problem.
(I also noticed HT has 400V instead of 340, which is just within tolerance, but you never know)
Current grounding:
Safety earth has it's own lug.
Second lug separate wires (power transformer CT) - (reservoir cap/first filter cap) - (second filter cap and the rest of the audio circuit ) - (volume knob) - (preamp tube bias resistor)
Non insulating output and input jacks are directly grounded to chassis (just using the mount, not wiring). I know it's probably not a good idea, but a lot of vintage amps get away with it.
Any advice would be appreciated.
No...
I use Hammond 290AEX transformer. It has no centre tap, and the voltage is 6.3V. I just twisted the wires tightly, and connected to the heater sockets. Not grounded.
I wanted to add virtual ground later, but with the amount of hum I'm getting now, I thought it couldn't be what is causing it? Or is it obligatory?
It is usual practice, with a centre tapped 6.3V heater winding, to ground the tap. I suspect you have no connection between the input jack and ground.
I installed 2x 100 ohm resistors from heater to the ground and it reduced hum dramatically. Thanks!
I used this setup before, but now never realized how much difference it can make.
Now it is at an acceptable level. I think I can improve it by cleaning up the wiring etc. I'll also try a humdinger pot.
I used this setup before, but now never realized how much difference it can make.
Now it is at an acceptable level. I think I can improve it by cleaning up the wiring etc. I'll also try a humdinger pot.
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