Hi,
I am using a laptop power brick. I've tried with other laptop charger and a wall wart too and the problem persists.
Evem that way, I think I will add a cap to the DC input of the amp.
I am using a laptop power brick. I've tried with other laptop charger and a wall wart too and the problem persists.
Evem that way, I think I will add a cap to the DC input of the amp.
I tried to put capacitors of several values at the input of the amp and at the output of the buck and nothing.
Tried from 0.1uF up to 2200uF.
I am wondering if I connect the pin of the volume potentiometer that now is connected to ground, to a resistor in series which connects to ground would improve this.
In this way the pot wouldn't be connected directly to ground any longer.
Tried from 0.1uF up to 2200uF.
I am wondering if I connect the pin of the volume potentiometer that now is connected to ground, to a resistor in series which connects to ground would improve this.
In this way the pot wouldn't be connected directly to ground any longer.
It might also be a ground loop. Is the circuit in a metal box? Otherwise the wires could be inducing it somehow.
Is the negative side of the speaker ( or output transformer) connected to ground? I also had some noises with the speaker floating.
Is the negative side of the speaker ( or output transformer) connected to ground? I also had some noises with the speaker floating.
Hi Thomas,
Initially I had problems due to the negative of the speaker not being grounded, but I fixed that some time ago.
The box is ABS plastic. I touched the transformer wires but they don't have any impact on the sound.
I think I will disconnect the boost and apply 12V directly to HT and see if there is buzz, then disconnect the buck, put a 7806 and check again.
Those are the only voltages sources in the circuit and one must be the guilty one.
Initially I had problems due to the negative of the speaker not being grounded, but I fixed that some time ago.
The box is ABS plastic. I touched the transformer wires but they don't have any impact on the sound.
I think I will disconnect the boost and apply 12V directly to HT and see if there is buzz, then disconnect the buck, put a 7806 and check again.
Those are the only voltages sources in the circuit and one must be the guilty one.
If you pull V1-A and the amp still isnt quiet regarding 50 Hz, you may need to add a balance to the output stage.
The ground referenced 270K (grounded at same physical point?) for the grids should have the output tubes operating at the same current, which would theoretically cancel the 50Hz hum on B+ in the output transformer.
Sometimes the tubes arent perfectly identical. A balance pot - guessing 50 Ohms - between the cathodes, with the wiper connecting to the 150 (or need it 125 now?) Ohm cathode resistor, may allow you to swing the (-) bias toward whichever tube is conducting a little bit more. Hopefully enough to null your hum.
You could also look at the spectrum across across the 270K on V1-Bs grid. Should have no DC across it, if the upstream cap is good. If the 50 hz is there, then it's for sure excessive on whatever B+ power you're using. Post a schematic of that too.
Hope it helps,
The ground referenced 270K (grounded at same physical point?) for the grids should have the output tubes operating at the same current, which would theoretically cancel the 50Hz hum on B+ in the output transformer.
Sometimes the tubes arent perfectly identical. A balance pot - guessing 50 Ohms - between the cathodes, with the wiper connecting to the 150 (or need it 125 now?) Ohm cathode resistor, may allow you to swing the (-) bias toward whichever tube is conducting a little bit more. Hopefully enough to null your hum.
You could also look at the spectrum across across the 270K on V1-Bs grid. Should have no DC across it, if the upstream cap is good. If the 50 hz is there, then it's for sure excessive on whatever B+ power you're using. Post a schematic of that too.
Hope it helps,
Hi Guys,
On my amps, I have put a bias pot on the cathode of a preamp valve, but it scratches when I rotate it. Is there a fix for this ?
Kind regards,
Pedro
On my amps, I have put a bias pot on the cathode of a preamp valve, but it scratches when I rotate it. Is there a fix for this ?
Kind regards,
Pedro
This message will go on both threads I have opened, so I can capture people that are only in one of them.
To thank you all for your support and sharing your knowledge with me, which gave me countless hours of fun, I would like to send you for free one PCB of one amp that you would like to try yourself.
I have basically two amps:
1 - Based on Fender Champ (Winner Slug)
2 - And a very low-power push-pull (Tiny Slug) based on the Superfly.
I can send you the PCB for free. Just pick one.
If you decide to build one, please give me your feedback: good, bad, so-so, garbage!
Have fun and Happy Easter.
Kind regards,
Pedro
To thank you all for your support and sharing your knowledge with me, which gave me countless hours of fun, I would like to send you for free one PCB of one amp that you would like to try yourself.
I have basically two amps:
1 - Based on Fender Champ (Winner Slug)
2 - And a very low-power push-pull (Tiny Slug) based on the Superfly.
I can send you the PCB for free. Just pick one.
If you decide to build one, please give me your feedback: good, bad, so-so, garbage!
Have fun and Happy Easter.
Kind regards,
Pedro
