Sansui 1000 hum? What does the HUM. Balance 100 ohm do?

[noise415]

Can you indicate how loud the buzz is with the vol pot at min relative to at max ?
With vol pot at min, does the buzz change in level with different Selector switch settings?
Can you hear any buzz with the 12AX7 removed from the noisy channel? (Also change Mode switch settings and Balance pot settings).

thanks for the advice.
1. with the 12AX7 removed buzzing is gone or at a barley audible level.
2. level of the buzzing sound with headphones with volume down is fairly faint. Adjusting volume knob to 5 increases about 5 dB up to 7 buzzing increase past 7 and noise floor is louder than the buzz.
3 buzzing remains the same with selector on different inputs. Tape input sounds a little different but I'm thinking this must have an eq or something.
4 When playing with speakers the buzz isn't much of a distraction.

I wonder if I'm expecting too much from this amp or should I be able to remove this buzzing? Other than this hiccup I love the sound of this amp.

 

[trobbins]

Main circuitry focus appears to be from the Vol pot to the first 12AX7 triode and possibly into the tone networks.

This assumes it is a 'fault', and was not happening prior to the rework you did. If so, then it may be related to your rework, as you may have moved wiring or caused a cold solder joint related to C78 (20uF 350V) that is common to the 12AX7 stages. Perhaps recheck that aspect first.

Perhaps check the Vol pot to see if some contact cleaner can be sprayed internally to clean the track and wiper contact - some pots are totally enclosed (which makes this task quite onerous) - you would need a spray can of electrical contact cleaner/lubricant with the long thin plastic nozzle attachment. Such a cleaner can also clean the 12AX7 socket/pins with a light drizzle into each socket pin and some valve insertion wiping.

Imho after that it gets a bit electrical and requires bench work, with some plausible steps being:
- the addition of a temporary shorting link across 1M R73 (or R74 depending on channel with buzz) to rule out the Volume pot and coupling cap and associated wiring.
- temporarily lifting one leg of coupling cap C79 (or C80) to rule out the tone control circuitry and wiring.
- resoldering all joints related to the triode and its direct circuitry.
- replacing anode then cathode resistors, and cathode bypass cap.