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Adcom GFA-2 service manual?????

englissa

englissa

Active Member
Evening All I bought a Adcom gfa-2 a while back and just now got to messing with it. It seems to operate ok but when i checked DC offset one channel is around 40 mv the outher is around 10mv. I would like to adjust this and bias but without a service manual i'm not going to. I looked everyplace i know where to look, googled for it , sent a message to Adcom asking about it with no reply so I'm asking here if anybody knows where i can get one or know how to adjust bias and offset . thanks Englissa
 
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Most Adcom's don't have an adjustment...some just rely on transistor matching, and some others use a DC servo to cure offset.

Adcom still sells manuals for all their old gear, which is why no one else does. Call them on the phone, and for $15 or so they'll sell you one. Why? Because until you know how it is built, you won't know how to address the problem (small though that problem may be).
 
Echowars I emailed them but got no responce,, Ok i will give them a call . How far does dc offset have to be before it is a problem ? englissa
 
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I guess you'd have to define 'problem'. Sonic problem? Or danger to the equipment?

As far as sonics, in my book anything over 20mV is an issue, and anything over 50mV needs attention (of course, if there's an adjustment, it gets adjusted).

Damage to gear (such as speakers)? You're several orders of magnitude away from that. Need at least a couple of volts for things to start freaking out.
 
Echowars When i first powered it up it stayed in protection for a few minutes then clicked on,,after that it came on in about 10 sec, thought maybe dc offset is at it limit for protection to kick in, maybe there are outher issures i'm not aware of ?????????
englissa
 
englissa said:
Echowars I emailed them but got no responce,, Ok i will give them a call . How far does dc offset have to be before it is a problem ? englissa
Click to expand...

Don't be surprised if it takes a few phone calls to get through. And don't hold
your breath waiting for a return email. Great gear, lousy customer service IMHO.
 
Welll Adcom answered me and sent a PDF file service manual,, dam shame it isnt more readly readable but i think i can make out what i need, here is the service manual, If can add it to this mail englissa
 

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englissa said:
Welll Adcom answered me and sent a PDF file service manual,, dam shame it isnt more readly readable but i think i can make out what i need, here is the service manual, If can add it to this mail englissa
Click to expand...
I was just tasked with setting the offset on a old (but nice and clean!) GFS-2 and discovered this website, and have to add that schematic I just downloaded is really bad! I wasn't able to make out the location of the test points but I am certain I can find the emitter resistors and will have to just "wing it" I suppose...
If you happen to read this, I wonder if you ever get a better copy?
rf
 
rfburnz I'm sorry but the poor copy i got from then is all I have, It took me a while but I figured it out, If you need help PM me and I'll see what I can do for you , once you figure out the test points its simple englissa
 
What they sent me is nothing more than a copy of what was e-mailed to me, yea it was a bitch to figure out but I did it , Yes it was FREE englissa
 
Hi
I am trying to adjust the DC balance and offset but can’t read the voltage setting in the service manual. It’s “X” V +/- 50mV. Does anyone know what it should be? Thanks for your help.
 
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