Hum Question

[blackharp]

Adjusting hum balance, I am only able to get it down to about 7.4 mV. Normal or a little high? Would the DC supply change the sound and in what ways?

[Paul Birkeland]

I would be sure that the 22 ohm and 0.51 ohm resistors are well soldered.  The DC filament upgrade will knock that down to below 1mV.

[blackharp]

Thank you, sir. I have read the DC supply can change the sound and make it "less transparent." Is there some truth to this, or is it a myth? Does it add or subtract anything? I love the sound as is... It could possibly use a little lower mid range but I'm comparing to a II, and it is more forward and has better separation.

[Paul Birkeland]

Adding the DC filament supply will remove hum sidebands that shouldn't otherwise be there, so there is a loss of something I consider to be undesirable. 

There used to be a lot more AC filament purists for SET amps, but that herd seems to be thinning out thankfully. 

[blackharp]

Ha! I love the honesty.

[Larpy]

I have a Kaiju that I built with the AC heater supply and after a couple of weeks I installed the DC heater supply.  Maybe (maybe) I heard a difference in the amp's sonic signature, but if I did it was neither better nor worse.  Just different. 

But whatever change there might have been was swamped by the reduced noise floor.  Even if the amp sounded ever so slightly worse after changing to DC (which it didn't), it was worth it just to hear no hum from my listening chair.