I've finished modding up my T amp. It's pretty good actually. I put it all in a small Hammond diecast box, painted bright red. I put a regulated 13.5 volt power supply in there.
Initially, I changed the input caps to be 15uF, but this caused a huge power-on transient. The larger caps didn't seem to help the sound at all, so I took them out and left it with the stock caps.
I added a larger electro in parallel with the on board PSU filter cap. I rewired all the input, power, and output circuitry with better wire & conenctors etc. I kept the stock output caps across the speaker terminals.
I use the stock volume control and power switch, but I'm switching the AC line with the switch, instead of the DC. This all works fine.
The only problem I have is that I hear power supply noise when the volume pot is in the middle third of its travel. It sounds like 120 Hz sawtooth noise. It goes away completely as the volume approaches maximum.
Before you jump on me, I checked that it's not caused by routing the AC line through the volume control switch. I took that off, and it made no difference at all.
It seems to me that the amp input impedance must be high enough that when the pot is in the middle, which is when it has highest resistance to ground and to signal, some radiated noise can be picked up. Yet moving the PSU further from the amp doesn't help. Could be picking up noise from the DC power signals, I guess. Maybe I should shield them.
Any clues about how to trouble shoot this? Anyone noticed anything similar?
Initially, I changed the input caps to be 15uF, but this caused a huge power-on transient. The larger caps didn't seem to help the sound at all, so I took them out and left it with the stock caps.
I added a larger electro in parallel with the on board PSU filter cap. I rewired all the input, power, and output circuitry with better wire & conenctors etc. I kept the stock output caps across the speaker terminals.
I use the stock volume control and power switch, but I'm switching the AC line with the switch, instead of the DC. This all works fine.
The only problem I have is that I hear power supply noise when the volume pot is in the middle third of its travel. It sounds like 120 Hz sawtooth noise. It goes away completely as the volume approaches maximum.
Before you jump on me, I checked that it's not caused by routing the AC line through the volume control switch. I took that off, and it made no difference at all.
It seems to me that the amp input impedance must be high enough that when the pot is in the middle, which is when it has highest resistance to ground and to signal, some radiated noise can be picked up. Yet moving the PSU further from the amp doesn't help. Could be picking up noise from the DC power signals, I guess. Maybe I should shield them.
Any clues about how to trouble shoot this? Anyone noticed anything similar?