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Setting Bias - Adcom GFA-555

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I have a Adcom GFA-555 amp that I have went through and replaced all capacitors, even the large filter caps. My dc offset is setting pretty at 9mv per channel but I was wondering if you would touch the bias.

What effect would it have on the amp if the bias were off?
 
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To low --distortion.To high-- over heating. Wouldn't hurt to check it.
 
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ouimetnick said:
But if for some reason the bias was set to low, no damage will occur.. just crummy sound?
Click to expand...

That's generally correct, but I've repeatedly confirmed that increased distortion caused by low bias isn't necessarily noticeable to the user. Music signals have an astounding capacity to mask amplifier noise and distortion, which leaves me deeply skeptical of all unsubstantiated claims regarding amplifier performance improvement.
 
I got the amp all put together over the holidays. Changing those 26 year old filter capacitors significantly changed the sound. More musical. Less muddy. Greater detail.

The amp could use a bias checkup but I am having a terrible time finding documentation on adjusting it. I have a GFA-555 service manual but it contains the procedure for a PS board unlike mine. They may be similar enough that the procedure also pertains to it but I would like to run it by the forum. Hopefully some of the past Adcom techs will chime in or others who have the same board as mine.

Here is my board along with the link to the schematic:

Link to schematic: www.civilwarmedicalbooks.com/bias/hfe_adcom_gfa-555_schematics.pdf

My GFA-555 PS board:

PS.jpg




Here is the link to the only GFA-555 service manual I can find which has the bias alignment procedure in it. Remember the board in this manual differs from mine:

www.civilwarmedicalbooks.com/bias/Adcom_GFA-555_service_manual(1).pdf

Here is board the top link refers to:

other
 
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