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!
someone mentioned PS upgrade article by 'Kit Ryan' but cannot find any more info on that.
Charles
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!
someone mentioned PS upgrade article by 'Kit Ryan' but cannot find any more info on that.
Charles
The Ryan mod was regulation. Nothing exotic, but a good design for a feedback series regulator on each rail. I would guess that the transistors used would not be trivial to get today.
I still have my 1985-vintage 555 up and running. Very nice amp, perfectly stable and reliable for nearly 30 years of (often) hard use. These days, it powers my mid-woofers. I had it modded for use with a servo system for a while, but it's now back to stock.
I still have my 1985-vintage 555 up and running. Very nice amp, perfectly stable and reliable for nearly 30 years of (often) hard use. These days, it powers my mid-woofers. I had it modded for use with a servo system for a while, but it's now back to stock.
thanks, SY
I was wrong about the PS caps. This morning I opened the old box containing all my electronic parts, and I saw in there 2 ADCOM 15,000 uF, 100V caps. So I must have replaced them with some other large caps. The replacement caps barely fit inside the amp. One of these days I should open it up and take some picture and jot down some notes.
Box also contains a box of Panasonic P-series polypropylene capacitors, some Sidereal poly caps, some special wires for coil windings (forgot why they were audio-grade 'special' though
, metal-film resistors, etc.
If I can find the documentations on what I did, then perhaps I could even find myself another GFA-555 and modified it so that I can bi-amp my speakers.
The TAA article probably came from 1986-88 issue. Anyone still have TAA issues from back then? Thanks!
I was wrong about the PS caps. This morning I opened the old box containing all my electronic parts, and I saw in there 2 ADCOM 15,000 uF, 100V caps. So I must have replaced them with some other large caps. The replacement caps barely fit inside the amp. One of these days I should open it up and take some picture and jot down some notes.
Box also contains a box of Panasonic P-series polypropylene capacitors, some Sidereal poly caps, some special wires for coil windings (forgot why they were audio-grade 'special' though
, metal-film resistors, etc. If I can find the documentations on what I did, then perhaps I could even find myself another GFA-555 and modified it so that I can bi-amp my speakers.
The TAA article probably came from 1986-88 issue. Anyone still have TAA issues from back then? Thanks!
hi Mayank,
thank you for your help.
Are you still interested in GFA-555 mod? I was very pleased with the modifications and the amp sounded great. I did a A/B comparison at the time to Jeff Rowland amp, and JR was better, but JR was also 3x or 4x more $ than my Adcom (even with all the extra $ that went into Adcom mod). Still driving my Magnepan IIIa today with the Adcom and think this combo still beats many of the 'hi-end' audio systems.
You should do the mod. You will be very happy with the improvement.
Regards,
Charles
thank you for your help.
Are you still interested in GFA-555 mod? I was very pleased with the modifications and the amp sounded great. I did a A/B comparison at the time to Jeff Rowland amp, and JR was better, but JR was also 3x or 4x more $ than my Adcom (even with all the extra $ that went into Adcom mod). Still driving my Magnepan IIIa today with the Adcom and think this combo still beats many of the 'hi-end' audio systems.
You should do the mod. You will be very happy with the improvement.
Regards,
Charles
GFA-555 Kit Ryan Mod
Charles:
I found and scanned the Kit Ryan mod article for you. Please PM me your email and I'll be happy to upload it for your records.
Over the years, I've owned/repaired/rebuilt several GFA-555's and continue to enjoy them in my main audio set up. I'd be very interested to know from you (and any others) who have built the Kit Ryan mod for their Adcoms - is the result as dramatic as claimed by the author. I am not sure from the thread above if the mods you performed in your "younger" days were the Kit Ryan PSU mod or other modifications
And of course, as Sy also mentioned, the million $ question - can someone recommend newer devices for the 2SA1095/2SC2565 in the original article?
I'd love to take on this project.
Rgds
Mayank
Charles:
I found and scanned the Kit Ryan mod article for you. Please PM me your email and I'll be happy to upload it for your records.
Over the years, I've owned/repaired/rebuilt several GFA-555's and continue to enjoy them in my main audio set up. I'd be very interested to know from you (and any others) who have built the Kit Ryan mod for their Adcoms - is the result as dramatic as claimed by the author. I am not sure from the thread above if the mods you performed in your "younger" days were the Kit Ryan PSU mod or other modifications
And of course, as Sy also mentioned, the million $ question - can someone recommend newer devices for the 2SA1095/2SC2565 in the original article?
I'd love to take on this project.
Rgds
Mayank
Old thread, new life. I've owned my 555 since new in 1987. Original owner of the unit. I have the same PC board in mine (SM[screwhole]S 394V-0; dated 1986), as does member Pre-cd. I came here after running out of information at AK, trying to help out Pre-cd.
Do any of you good folks know if there are any substantial differences between the SM(screwhole)S 394V-0 board and the one that is listed in the manual (72-2174-0-1)?
Mr. Pass, do you have an idea what Adcom was up to in 1986-87 in regards to some of the manufacturing changes with the 555? I can't seem to find any information about the 2 versions used.
Love the amp, STILL, by the way
Fran640g:
Thank you for posting this here. Let me add some pics to this post.
Below is the board and printed circuit board that is in the GFA-555 service manual for the part number 72-2174-0-1:
Here is the GFA-555 board Fran604g and I have (part number SMKS 3940-0) and need the service manual for:
Thank you for posting this here. Let me add some pics to this post.
Below is the board and printed circuit board that is in the GFA-555 service manual for the part number 72-2174-0-1:
Here is the GFA-555 board Fran604g and I have (part number SMKS 3940-0) and need the service manual for:
Wow, Great picture! My board has the screw hole just low enough to obscure the "K." Yours is not obscured at all. Wonder if they were building these amps one at a time?
Really cannot say much at this point. I hope someone chimes in with a schematic for this board and service manual. I would like to recap the board and set the bias. The only difference I see in your board and mine is the small electrolytic caps. Mine seem to have been changed at some point as they are Nichicon and yours are the Towa caps.
I am sure those who know the answers to the schematic will give us a yell as time permits.
I did make a typo in my post in reference to my board's part number. It was supposed to be SMKS 394V-0. Fat fingers.....
Kevin
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