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Pioneer SA-8800 headphone hum

W

Wally C

Member
I’ve got Pioneer SA-8800 integrated amp. Recently I’ve replaced all caps (except main filter caps). Everything is very good. However when connecting headphones, I can hear fainted hum. It’s not related to volume though. I can hear it when volume is 0. When increasing the volume, the hum stays the same. To make this thing very weird, the hum is not audible through speaker terminals, even when I connect headphones (through 330 ohms resistor) directly to speaker terminal.

I’ve traced power amp output wires and here is how they are routed: L and R wires are routed from PCB through left side of the amp to speaker selector switch. From that switch the wires (L & R for Speakers A and L & R for Speakers B) are routed the same way back to speaker terminal. The speaker selector switch is also used to connect (through 330 ohm resistor) two additional wires to headphone ¼” jack. The main power switch is on the left, next to the headphone jack. Maybe this switch is causing the hum? I’m thinking about bypassing power switch and see if that get rid of the hum. Anyone who owns SA-8800 can comment on this?


Cheers…..
 
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Thanks for the link, but I already have service manual for this amp. It doesn’t look like this is a ground issue. It is also not related to power switch. The hum is more pronounced in right channel, roughly twice as loud as left channel. It is still very low volume though. Looks like I need to use my scope to trace the source of this hum. Will keep you posted….
 
Problem is fixed. I decided to re-route the headphone cable using shielded wire. I’ve connected this wire to the same points as the speaker wires (right after the relay). Now the hum is gone. Headphones are dead quiet
 
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