I recapped a pair of Adcom GFA-555 amps with Panasonic FC caps and everything is working great on both. Just today, I realized that I had used 50V rather than 63V for the 4.7uF C5 cap, which parallels the 1K bias trimmer pot. The part is shown almost dead-center in the included schematic.
(Explanation: I ordered the caps based on a schematic for the earlier production model with the vertical input board.)
Is there any reason, at all, to open up the amps and replace these caps? I can't imagine that 63V caps are needed there, but I'd like to hear from others.
(Explanation: I ordered the caps based on a schematic for the earlier production model with the vertical input board.)
Is there any reason, at all, to open up the amps and replace these caps? I can't imagine that 63V caps are needed there, but I'd like to hear from others.
An externally hosted image should be here but it was not working when we last tested it.
It's had 64 views and no one had any advice?
Could someone recommend another forum I might post this on? Would AudioKarma be a good bet for getting a response?
Could someone recommend another forum I might post this on? Would AudioKarma be a good bet for getting a response?
Well, the schematic calls for a 63V cap for C5, so that is what I would use (or higher). The caps are cheap, so I personally would put in the correct parts.
Certainly less than 3V
At a pinch you might feel safe with a 6.3 working voltage capacitor for C5.
A 63 volt working voltage component would have better ESR/impedance characteristics and would be more effective in that position. The choice of voltage rating would have perhaps have been made on those grounds.
I imagine the part you removed will have been a general purpose electrolytic (although I notice despite the appropriate symbol on the circuit diagram the notation "PP" appears alongside).
If correct the substitution of a low impedance cap such as a Panasonic FC would be an improvement regardless of the albeit slightly lower working voltage rating.
There is quite a lot of material on the GFA-555 on Diyaudio. It is mentioned somewhere in an interview with Nelson Pass. You may want to look this up.
mjona
A 63 volt working voltage component would have better ESR/impedance characteristics and would be more effective in that position. The choice of voltage rating would have perhaps have been made on those grounds.
I imagine the part you removed will have been a general purpose electrolytic (although I notice despite the appropriate symbol on the circuit diagram the notation "PP" appears alongside).
If correct the substitution of a low impedance cap such as a Panasonic FC would be an improvement regardless of the albeit slightly lower working voltage rating.
There is quite a lot of material on the GFA-555 on Diyaudio. It is mentioned somewhere in an interview with Nelson Pass. You may want to look this up.
mjona
Thank you to all who responded, including a one Mr. Nelson Pass, who responded via e-mail. mjona, you should be pleased to see that Nelson Pass wrote:
Nelson Pass said:
You just can't say enough good things about Nelson Pass.
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