Adcom GFA-555 Cap Question: 50V vs 63V - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 8th June 2012, 12:16 AM   #1
diyAudio Member
 
Join Date: Jan 2012
Default Adcom GFA-555 Cap Question: 50V vs 63V

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.

Click the image to open in full size.
  Reply With Quote
Old 8th June 2012, 04:19 PM   #2
diyAudio Member
 
Join Date: Jan 2012
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?
  Reply With Quote
Old 8th June 2012, 06:04 PM   #3
diyAudio Member
 
Join Date: May 2008
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.
  Reply With Quote
Old 8th June 2012, 06:31 PM   #4
lms is offline lms  Micronesia
diyAudio Member
 
Join Date: Aug 2004
Location: beach
cap has 2.5v max across it, 50v cap is fine
  Reply With Quote
Old 8th June 2012, 07:17 PM   #5
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Quote:
Originally Posted by lms View Post
cap has 2.5v max across it, 50v cap is fine
Certainly less than 3V
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 8th June 2012, 07:34 PM   #6
diyAudio Member
 
Join Date: Nov 2004
Location: Germany
And in case it ever becomes more, one electrolytic will probably be the least of your worries...
  Reply With Quote
Old 8th June 2012, 08:58 PM   #7
mjona is offline mjona  New Zealand
diyAudio Member
 
Join Date: Jul 2007
Location: Upper Hutt
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
  Reply With Quote
Old 8th June 2012, 10:20 PM   #8
diyAudio Member
 
Join Date: Jan 2012
Quote:
Originally Posted by mjona View Post
At a pinch you might feel safe with a 6.3 working voltage capacitor for C5.
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:

Quote:
Originally Posted by Nelson Pass
The bias trimmers only see a few volts. Minimum for those would be 6.3V.

best, np
You just can't say enough good things about Nelson Pass.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Adcom gfa 555 help 406vette Solid State 34 15th October 2011 03:34 PM
Adcom GFA-555 MK II P/S cap position embrown057 Solid State 1 1st September 2010 06:00 AM
Adcom GFA-555 Feedback DC-Blocking Cap? EchoWars Pass Labs 14 14th April 2010 07:12 PM
Adcom GFA-555 eelekim Pass Labs 2 14th May 2009 03:42 PM
FS:Adcom GFA 555 and GFA 5300 trusound Swap Meet 0 13th December 2005 05:06 PM


New To Site? Need Help?

All times are GMT. The time now is 01:15 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2