Adcom GFA-5500 bias/DC offset

RyanJoz

I recently adjusted the bias on my GFA-5500. The bias voltage prior to starting was 7.9mA for the left channel and 7.9mA for the right channel. The factory service manual states these should read 50mV +/-5mV.

I now notice static more than I did previously. Did I miss something in the manual? I disconnected the pre-amp and speaker connections to make the bias adjustments. I work for a company that has calibrated meters so I brought one home from work to adjust the amplifier.

The DC offset measures 4.5mV (L) and 5.4 mV (R) so both channels are in the spec from Adcom.

This is the first time the amplifier was opened up as I bought it new about 3 years ago. The amp used to run cold as ice and now warms up similar to how my receiver does. The amp also used to have very poor bass response (suggested by VR3 to check/adjust the bias)

Thanks in advance.

RyanJoz

bias was in mV, not mA. It was a typo.

SugarmillMan

Can you translate for us common types?

RyanJoz

the bias was set too low according to the factory service manual. have you had issues with static after adjusting the bias? The amp now warms up nicely, where it ran ice cold before.

The bias started out around 8 mV before adjustments and the service manual states that it should be at 50 mV.

Bass response has drastically improved, but there is some static/distortion in the midrange at certain frequencies.

Hopefully this description will help more.