SA-9900 - Preamp low volume hum

[Jerry's TV]

I understood from the user manaul that the FET should turn on after the protection relay. I'm sure either way is fine. My FET turn-on is like yours was... several seconds after the relay clicks.

 

[LesE]

True, it was designed that way. I always make sure that the volume is at minimum when powering up so there no signal present that would cause relay contact arcing and deterioration. So it's more a matter of personal preference for me.

 

[sajjad amer]

True, it was designed that way. I always make sure that the volume is at minimum when powering up so there no signal present that would cause relay contact arcing and deterioration. So it's more a matter of personal preference for me.

Following your footsteps when I ground pin 21 on aws-080 I loose right channel completely but hum on head phones completely disappears.
What is happening here?

 

[LesE]

Sajjad, just want to make sure you're on the correct board. AWS-080 is the Switch Assembly board which is accessible from the bottom of the amplifier. There should be a black wire on the pin that routes through to the top side of the chassis near the power switch. Pin 21 should already be grounded to the chassis but I found that there is roughly 0.5 ohms of resistace to ground which is providing an opening for hum to be introduced.

Is it possible that you are looking at pin 21 on the Control Amplifier board which is it's right channel signal output?

 

[sajjad amer]

Sajjad, just want to make sure you're on the correct board. AWS-080 is the Switch Assembly board which is accessible from the bottom of the amplifier. There should be a black wire on the pin that routes through to the top side of the chassis near the power switch. Pin 21 should already be grounded to the chassis but I found that there is roughly 0.5 ohms of resistace to ground which is providing an opening for hum to be introduced.

Is it possible that you are looking at pin 21 on the Control Amplifier board which is it's right channel signal output?

You are spot on, I was grounding pin 22, one with orange wire. My mistake, now connected pin 21 to ground and noise is even less than before. Thank you so much once again.