Adcom GFA-545 II Schematic Needed - diyAudio
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Old 27th October 2006, 03:48 AM   #1
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Default Adcom GFA-545 II Schematic Needed

Hello, I came across a sweet looking Adcom GFA-545 II with a few minor issues.
I was hoping someone out there might e-mail a Schematic and a bias adjust spec for this little jewel.
Many Thanks in advance

email me at: ebayer0u812@sbcglobal.net
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Old 29th October 2006, 05:01 PM   #2
anatech is offline anatech  Canada
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Hi justonemoreamp,
What problems are you having?

-Chris
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Old 30th October 2006, 12:19 AM   #3
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Hello, I have a burnt resistor tied to the emitter of Q605 and no burnt outputs, but blown fuses so I want to completely go thru the thing before restoring power to it.
It appears that it might have frontend damage as I have tested all the outputs and driver and they all appear to just fine.

Hence my request for a schematic. Overall it appears to be a very straight forward design, but I have read it has a offset servo up front and I would rather not second guess that section of the amp.

It also has Adcom marked Ic's up front and if they have been damaged I would like to see the circuitry to allow replacements to be picked tested and installed from my selection of AD and BB chips.

I already have a partial schematic of the output s and drivers section only ( i found that here on the forum) but no front end section is to be found ( I have scotch tape if and when i find it )

Plus I dont like to second guess and invent bias adjustments so hence my request for a bias spec. for the output stage. I normally repair amps all day long. So I can follow any instructions you might have to offer.

I just want to do this old girl justice and see the job completed properly and to spec. It will go nicely on my tech bench with my Adcom tuner preamp I use for a source everyday

Many thanks in advance for any support you might be able to render.
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Old 30th October 2006, 12:27 AM   #4
anatech is offline anatech  Canada
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Hi justonemoreamp,
The 100 ohm resistor for the current source is burned??? If that's true, the diff pair is toast, and probably Q605,Q615, D605, D607 and more.

Choose a low DC offset op amp for the Adcom 3A if you need to. It's filtered so there is no "sound" from it per se. Pin 7 should be running around +12 VDC supply. Check for capacitor electrolyte on the PC board just in case.

-Chris
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Old 18th September 2012, 03:11 AM   #5
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Default here's your schematic link--6 years later

Adcom manuals, schematics and brochures - Hifi Manuals

johnny on the spot
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