November 2019 Thread Update:
See posts 55, 62, and 63 for updated listening impressions. I executed on the upgrades offered by John Hillig at Musical Designs/Musical Concepts in the form of the LX Elite Mod with Mini-Platinum upgrade.
The results are just stunning.
I'm going to refer to the amp, in its current, highly modified state, as the GFA-"5500 MCEP".
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Original first post:
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I just acquired a used Adcom GFA-5500 two channel amplifier. it is the non-IEC power cord version. I took the liberty of checking bias and DC offset; the bias was quite low at under 15mV on each channel (service manual says 50mV +/-5mV). I adjusted both and it's stabilized at just over 49mV on each channel.
Next, I adjusted DC offset. Right channel was fine at .7mV. Left was way off at 19mV. Now they're both hovering around 1mV after temp has stabilized and some current run through the amp.
My issue: bass, while much improved from my first listen and now very tight and well damped, seems underwhelming.
Using my ir thermometer, there is a running difference between heat sink temps; roughly 117 for the left channel and 110 degrees F for the right channel across the face of the heat sink.
My question: Is this an indicator that I need to start looking at cap replacement? If so, which ones; the smaller low capacity caps on top (there are 8) or the four primary beer-can sized filter caps underneath them?
I checked the fuses and they are all functional (look normal and had continuity according to my fluke meter), but I'm going to replace them anyway as they are a hodge podge of mismatched brands. I know I know....blame the OCD.
Any input is appreciated. If I need service, I'm in the Orlando, FL area and am willing to drive quite a ways to avoid absurd shipping costs. Recs for nearby businesses are welcome (or far away ones with reasonable shipping costs).
Thanks in advance, gents.
Oh, and as a note, I'm coming from an Arcam AVR 300 with a healthy amp section itself. Using it as a pre amp now.
See posts 55, 62, and 63 for updated listening impressions. I executed on the upgrades offered by John Hillig at Musical Designs/Musical Concepts in the form of the LX Elite Mod with Mini-Platinum upgrade.
The results are just stunning.
I'm going to refer to the amp, in its current, highly modified state, as the GFA-"5500 MCEP".
****************************************************************
Original first post:
****************************************************************
I just acquired a used Adcom GFA-5500 two channel amplifier. it is the non-IEC power cord version. I took the liberty of checking bias and DC offset; the bias was quite low at under 15mV on each channel (service manual says 50mV +/-5mV). I adjusted both and it's stabilized at just over 49mV on each channel.
Next, I adjusted DC offset. Right channel was fine at .7mV. Left was way off at 19mV. Now they're both hovering around 1mV after temp has stabilized and some current run through the amp.
My issue: bass, while much improved from my first listen and now very tight and well damped, seems underwhelming.
Using my ir thermometer, there is a running difference between heat sink temps; roughly 117 for the left channel and 110 degrees F for the right channel across the face of the heat sink.
My question: Is this an indicator that I need to start looking at cap replacement? If so, which ones; the smaller low capacity caps on top (there are 8) or the four primary beer-can sized filter caps underneath them?
I checked the fuses and they are all functional (look normal and had continuity according to my fluke meter), but I'm going to replace them anyway as they are a hodge podge of mismatched brands. I know I know....blame the OCD.
Any input is appreciated. If I need service, I'm in the Orlando, FL area and am willing to drive quite a ways to avoid absurd shipping costs. Recs for nearby businesses are welcome (or far away ones with reasonable shipping costs).
Thanks in advance, gents.
Oh, and as a note, I'm coming from an Arcam AVR 300 with a healthy amp section itself. Using it as a pre amp now.