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Adcom GFA-555II
Adcom GFA-555II
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Old 31st January 2011, 08:12 PM   #31
yairf is offline yairf  Israel
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Join Date: Nov 2003
Location: Israel
Hi all
I'm contemplating a 555-II rebuild. from a first glance, I noticed some differences from MK1 to MK2, mainly the servo amp in the input stage. I wonder if this makes the amp any better (I doubt it!).
I have schematics for both - if needed send me a line to yfurman at bezeqint dot net.
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Old 2nd September 2011, 08:04 AM   #32
clin36 is offline clin36
diyAudio Member
Join Date: Aug 2011
hi all,

I modified my original 555 in late 80s. Mod was based on an article in The Audio Amateur.

I've lost all my TAA from years of moving around when I was younger. I would like to know exactly what I did (and reconstitute a good record of my beloved equipment), so does anyone know that exact article, and can help me locate a copy?

Without opening the amp cover, I believe it has 2 stacked toroidal transformers (instead of factory 1), and much higher PS capacitors (2x15,000 uF per channel), I also replaced with polyprolylene caps (Sidereal caps) and 1% metal-film resistors. Also involved changes in circuitry.

The amp sounded beautiful and still does today. Driving pair of Magnepan IIIa, pre-amp is Accuphase C-200.

After the mod I was interested in how it compare to some well-know high-priced power amp. I borrowed a Jeff Rowland and did A/B test. Well, Jeff Rowland still came out ahead, with more 'airiness', but for the money of 555 (and what I could really afford at that time), Adcom was good enough for me.

Anyway, I'd appreciate if someone can help me locate the TAA article. Thanks!

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Old 2nd September 2011, 08:41 AM   #33
clin36 is offline clin36
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Join Date: Aug 2011
BTW, I searched db and found mention of PS upgrade article by Kit Ryan but that is all I can find (not sure that was even the same article I used)
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