Adcom GFA-555 mods - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Closed Thread
 
Thread Tools Search this Thread
Old 22nd May 2016, 08:44 PM   #1
rellik is offline rellik  United States
Banned
 
Join Date: Oct 2005
Default Adcom GFA-555 mods

Mods to an amazing Adcom GFA-555 amplifier.

The transformer has been covered in athletic tape and has a slightly larger than semicircular piece of TI-shield to orient the magnetic field away from the system. This piece of TI-shield was filed on edges to reduce outwards transmission and enhance internal reflected dissapation as well as absorbtion by the transformer. The shield also functions to isolate the transformer from the capacitors to be located behind it. TI-Shield was baked at 600 in oven and slowly cooled to form a porous oxide layer to enhance absorbtion, surface dissapation, and reduce emission of both trapped and surface signals.

The lower bin will be filled with Urethane gel Shore-40. Other capacitor circuits will be in and outside the bin as well.

The transistors and gain/control board will be located in the upper bin which is to be filled with shore-40 urethane gel as well.

Other capacitors to be used are 6 groupings of Solen capacitors as well as 4 ASC capacitors.

Research to be done on speaker binding posts and RCA bindings and fuse holder, goal intended to keep costs low. Most likely will use original equipment included with Adcom GFA-555 save IEC recepticle where a fururtech is to be used.
 
Old 22nd May 2016, 08:48 PM   #2
rellik is offline rellik  United States
Banned
 
Join Date: Oct 2005
Photos:
Attached Images
File Type: jpg 20160522_152301.jpg (963.6 KB, 163 views)
File Type: jpg 20160522_152326.jpg (345.0 KB, 156 views)
 
Old 23rd May 2016, 05:24 AM   #3
diyAudio Member
 
Join Date: Jan 2004
Location: gold coast
That's a joke right?
 
Old 23rd May 2016, 08:09 AM   #4
rellik is offline rellik  United States
Banned
 
Join Date: Oct 2005
Nah, a ~kiloliter cinder block subwoofer with 12" woofer will tax even this setup pretty severely.

Should power a pair of the big paradigm entry level floorstanding speakers quite well with the polypropylene larger woofers swapped for the paradigm mini monitor metal coned woofer.
 
Old 23rd May 2016, 08:18 AM   #5
rellik is offline rellik  United States
Banned
 
Join Date: Oct 2005
Images of the mur840 soft recovery rectifiers. Attached to heatsinks.
Attached Images
File Type: jpg 20160523_031500.jpg (262.8 KB, 126 views)
 
Old 24th June 2016, 10:08 PM   #6
rellik is offline rellik  United States
Banned
 
Join Date: Oct 2005
Project has been modified to use original chassis with the 8 stacked Nichicon capacitors and shore-40 urethane gel. A NTC thermistor will be implemented along with a knife switch or deft plug switching to deal with the significant in rush current.

The center tap on the primary has two polystyrene film caps wrapped around the insulator along with two quarter watt 1k resistors. A cardas golden cross power cord has been attached to the chassis directly. Capacitors affixed using double sided automotive tape. Above shown rectifier bridges used.

The original project will be spurred to a new solid state design using a modified dynahi topology using higher current devices or the bins of Hfe tested transistors I have sitting around. Decision to follow circulatron 300b tube project.

Photos of adcom to come.

Last edited by rellik; 24th June 2016 at 10:37 PM.
 
Old 25th June 2016, 04:59 PM   #7
rellik is offline rellik  United States
Banned
 
Join Date: Oct 2005
I am simply just going to use a Variac and deftly switch the plugs. This thermistor simply isnt the right value.
 
Old 26th June 2016, 06:16 AM   #8
rellik is offline rellik  United States
Banned
 
Join Date: Oct 2005
I have added 4 polystyrene capacitors to the top of the Nichicon capacitors. Additionaly I have added a polystyrene capacitor to the top of the toroid placed underneath the input board. This polystyrene has two 5Kohm quarter watt metal film resistors taped non conductivly to the polystyrene capacitor.

Look closely at the attached photo for the polystyrene capacitors are quite close to level. The photo shows them as quite skewed in direction as well as horozonttality.
Attached Images
File Type: jpg 20160626_010741.jpg (470.6 KB, 57 views)

Last edited by rellik; 26th June 2016 at 06:22 AM.
 

Closed Thread


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
Fully restored ADCOM GFA-555 II with all the mods. $850 Phloodpants Swap Meet 1 17th October 2015 02:42 AM
Adcom GFA-555 davamp Pass Labs 11 11th August 2015 08:09 PM
Adcom GFA-555 eelekim Pass Labs 2 14th May 2009 04:42 PM
FS:Adcom GFA 555 and GFA 5300 trusound Swap Meet 0 13th December 2005 06:06 PM
mods for Adcom GFA 555 II vad69 Solid State 2 27th June 2004 01:39 AM


New To Site? Need Help?

All times are GMT. The time now is 11:12 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright 1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki