Adcom GFP-565 OpAmp question

KT · 8th July 2007, 07:24 AM

Hello, I'm considering replacing the gainstage chips and main ouput buffers of my GFP-565 with OP627's and BUF634's, respectively. Unfortunately, I didn't purchase the AudioXpress GFP-565 modding issues when they were available and the service manual I purchased from Adcom many years ago has disappeared over the course of time. On the Adcom board, there's a stage with chips labeled IC201 and IC202, a stage labeled IC205 and IC206, and another stage labeled IC401 and IC402. I think that one of these is the gain stage, one is the output buffer stage, and one is the tape out buffer stage, but I'm not sure which is which. If someone could shed some light on which stage is which, I would greatly appreciate it. Thanks! KT

TerryC · 10th July 2007, 12:14 AM

201, 202 gain/buffers
205, 206 tone controls
401, 402 tape out buffers

This may be helpful as well...

ADCOM GFP 555II upgrade question

The AudioXpress articles are invaluable, but go way beyond simple componenet swap out. Back issues can be purchased from their website. Reproductions of the service manual are available from mutliple sources on the web.

KT · 10th July 2007, 08:02 AM

Thanks, Terry This information helps a lot. When the AudioXpress articles came out, I was really tempted to get them. I had so many preamp projects in the pipeline at the time, though, that I passed. I should have sprung for them though. Well, now I'm upgrading the chips since I have the OPA627s. I always thought the GFP-565 was a marvelous performer. A good all-around preamp that doesn't hype up any particular aspect of the sound. Just solid and musical. I'll probably purchase the AudioXpress CDs at some point, but for now thanks for the info. I'll just change out the opamps for now and slowly work towards the full mods later. Best, KT

8th July 2007, 07:24 AM	#1
KT diyAudio Member Join Date: Oct 2003 Location: USA	Adcom GFP-565 OpAmp question Hello, I'm considering replacing the gainstage chips and main ouput buffers of my GFP-565 with OP627's and BUF634's, respectively. Unfortunately, I didn't purchase the AudioXpress GFP-565 modding issues when they were available and the service manual I purchased from Adcom many years ago has disappeared over the course of time. On the Adcom board, there's a stage with chips labeled IC201 and IC202, a stage labeled IC205 and IC206, and another stage labeled IC401 and IC402. I think that one of these is the gain stage, one is the output buffer stage, and one is the tape out buffer stage, but I'm not sure which is which. If someone could shed some light on which stage is which, I would greatly appreciate it. Thanks! KT

10th July 2007, 12:14 AM	#2
TerryC diyAudio Member Join Date: Jun 2005 Location: WA-USA	Re: Adcom GFP-565 OpAmp question 201, 202 gain/buffers 205, 206 tone controls 401, 402 tape out buffers This may be helpful as well... ADCOM GFP 555II upgrade question The AudioXpress articles are invaluable, but go way beyond simple componenet swap out. Back issues can be purchased from their website. Reproductions of the service manual are available from mutliple sources on the web.

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10th July 2007, 08:02 AM	#3
KT diyAudio Member Join Date: Oct 2003 Location: USA	Thanks, Terry This information helps a lot. When the AudioXpress articles came out, I was really tempted to get them. I had so many preamp projects in the pipeline at the time, though, that I passed. I should have sprung for them though. Well, now I'm upgrading the chips since I have the OPA627s. I always thought the GFP-565 was a marvelous performer. A good all-around preamp that doesn't hype up any particular aspect of the sound. Just solid and musical. I'll probably purchase the AudioXpress CDs at some point, but for now thanks for the info. I'll just change out the opamps for now and slowly work towards the full mods later. Best, KT