Deluxe Reverb Build Noise When Adjusting Volume Pot

[cbdavid]

Hello Amp Builders!

My name is Christian and I have recently completed my deluxe reverb build and it sounds incredible! I am overjoyed with it other than the noise! However, as mentioned I'm having a noise issue. When I adjust the volume pot I get the noise you can her in the linked video:

https://youtube.com/shorts/u8lSayqNZVA? ... Bfdy8GIEVm

I have been following Robrobs troubleshooting and have replaced some troublesome tube sockets and removed tubes according to his guide but the problem persists no matter the tube configuration. I'm ready to provide any and all needed information I'm just not sure what needs to be shared initially. If you have time I would really appreciate the help! I'm a little lost on next steps and am very motivated to get this working. I have searched the forum but couldn't find a similar issue however if one exists with a method to fix it please leave a link.

Thanks,
Christian

[pdf64]

There's a cable plugged into the channel input, what's it connected to?
Does the amp noise change if that cable is removed?
The point being that an open cable will pick up that kind of EMI buzz. So we need to eliminate that as a possible noise source.

With the amp unplugged from the mains wall outlet and its power supply caps discharged, what resistance do you measure between the chassis metal and any lug of the 6.3V heater circuit?
The heaters of signal path valves need a low impedance, and a resistive path, to circuit common. Without that, they can transmit buzz through the cathode, and via magnetic field coupling, into the signal path.

[cbdavid]

Thanks for the reply, I should have unplugged the cable before the video. The noise does not change with it unplugged.

Onto the heater to chassis ground impedance (unplugged and discharged). Between two connected points within the heater circuit the impedance is low at ~0.21 ohms. The heater circuit to ground is an O.C and therefore is too high to measure on my instruments. This is what I should expect though no?

[pdf64]

... The heater circuit to ground is an O.C and therefore is too high to measure on my instruments.

The resistance should typically be near 0 ohms or 50 ohms. As it reads OC (open circuit I suppose) your build seems that it might be lacking any reference for the 6.3V heater circuit to circuit common (chassis 0V, ground).
Typical methods are for a heater winding centre tap connected to the chassis, or a pair of 100R heater circuit balancing resistors.
Implementing one or the other of these will probably fix the noise.
Does the mains power transformer heater winding (typically a pair if green wires) have a centre tap (typically a green/yellow striped wire)?

Do you have a pair of 100R 1/2W resistors left over?

Watch out to avoid confusing 100R (100 ohms) with 100k (100,000 ohms).

[cbdavid]

Somehow I missed connecting the heater winding centre tap to the chassis as I was following a variety of different build guide. I connected it to the chassis and it made a huge improvement and now there is just noise to deal with. Over the weekend I will trace the circuit and make sure all my grounds are good to see if I can reduce the noise. Also my tremolo circuit boosts the volume but does not provide the tremolo effect so I will need to troubleshoot that as well.

Thank you very much for your help. I hope your family's charity drive goes well, I've tried to donate to support them but my bank has denied it. I will try again later.

[pdf64]

.., now there is just noise to deal with.

I'm pleased you've got rid of the buzz!
Could you make another video demonstrating this noise?

Thank you very much for your help. I hope your family's charity drive goes well, I've tried to donate to support them but my bank has denied it. I will try again later.

Thanks, sorry it didn't work, please see whether donating directly to the STXBP1 Foundation is more successful?https://give.stxbp1disorders.org/give/3 ... n/checkout
https://www.stxbp1disorders.org