A few Adcom GFA 555 questions

[Bruce Morgen]

Don't know about that but I will say I'm a bit squeamish on the later lines of Adcom amps. I can't say exactly why, but there were some issues like the failed power supply caps on the 565s IIRC, etc I stick with the 535-545-555 lines since they seem to last forever and measure great.

Yeah, I have to testify that my GFA-535 never gave me a lick of trouble. I think the horror stories began when Adcom cut Nelson Pass out of the loop and lesser engineers were tasked to upgrade/upscale the original designs.

 

[raindance]

If an older Adcom doesn't have any hum, the chances are it's doing ok. It's very hard to desolder the caps in some of these amps; I replaced the caps in a GFA5500 and it's not a task I'd like to repeat. But typically if they don't hum and they hold bias and dc offset is low, then they're ok. A lot of failures seem to be due to bias drifting too high, probably from transporting them.

Setting bias and offset takes a good multimeter, an insulated "tweaker" and a steady hand

Someone recommended a Parasound amp. They're pretty reliable and have good speaker protection circuitry, even the cheaper series than the A23 that was recommended. They also have a bias drift issue, due to a very cheap trimpot used for bias, and this trimpot generally needs replacement. They sound very good.

 

[SIY]

Ok thanks! My top two choices right now are Adcom gfa-565se or Van Alstine Set 400!

No brainer there- not because of sound (which won't be different until clipping) but reliability and bench performance. Van Alstine's stuff is... variable.

 

[Plcamp]

I have recently revamped two 535II amps, one of which was hacked. I found them delightfully easy to work on. They both perform great now.

biggest things I found…

- All caps were good.
- one unit had feedback path trace cut for a capacitor insert, unsurprisingly the input bjt diffpair was widely out on gain match. Fixed that and dc offset opamp worked perfectly.
- other unit had a slighter but still 15% gain mismatch, fixed that.
- biggest job was cleaning the pcb
- all led holders were rusty.
- bias was out only on the hacked unit.

 

[bhu1kaura]

I recently bought a gfa 555 ii, for 33K INR.. The amp is in good condition. Still I want to replace all the aged components inside it.. I'll be driving Bryston Model T ( with external crossover ) with it.

I'd need your guidance on getting the replacement done. Is it worth it? I am willing to ship it outside India, if absolutely needed. Could you please suggest a couple of experienced professionals who do these kind of jobs in India, or abroad.

I have a pair of Hypex amps from Audiophonics.fr. Just want to see how the 555 sounds when compared to this one.

Many thanks in advance.

Regards,
Bhuwan

 

[Doodski]

I recently bought a gfa 555 ii, for 33K INR.. The amp is in good condition. Still I want to replace all the aged components inside it.. I'll be driving Bryston Model T ( with external crossover ) with it.

I'd need your guidance on getting the replacement done. Is it worth it? I am willing to ship it outside India, if absolutely needed. Could you please suggest a couple of experienced professionals who do these kind of jobs in India, or abroad.

I have a pair of Hypex amps from Audiophonics.fr. Just want to see how the 555 sounds when compared to this one.

Many thanks in advance.

Regards,
Bhuwan

Have you tested the Adcom amp? Have you run a torture load test and checked for ripple at the power supply caps? Before replacing parts you should test the amp and see if there is anything actually wrong with it.

 

[GXAlan]

I have one from the same era ('85). All it's ever done is work. You can find modern amps that have better measurements, but they won't sound any different.

I used to run these as bridged monoblocks with a bypass capacitor used to “improve the sound”. I ended up getting a Parasound amp and preferring the “warmer” sound.

This was back in the dark ages. I really wonder what I was hearing, if anything or if it was all sighted bias.

I was probably running under 5W of power anyway.

 

[bhu1kaura]

Have you tested the Adcom amp? Have you run a torture load test and checked for ripple at the power supply caps? Before replacing parts you should test the amp and see if there is anything actually wrong with it.

I don't have the gear/expertise to test it. But the left channel has a lot of constant hum/noise. Right channel works fine. When switched off, it makes crackling sound only in the left channel. Might be because of transportation.

For peace of mind, I want to overhaul it once so that it does not trouble me for the next couple of decades atleast.

Any references in this regard will be helpful.

Thanks!

 

[Sal1950]

I'd need your guidance on getting the replacement done. Is it worth it? I am willing to ship it outside India, if absolutely needed. Could you please suggest a couple of experienced professionals who do these kind of jobs in India, or abroad.

Wish I could help you on recommending a tech but the two pro's I knew of here in the US
have both retired.. I use 5 Adcoms here in my 5.2.4 multich rig, 2 GFA 545 II's, 1 5400, and 2 535 II's.
They are incredibly long term reliable and nothings been replaced in any of the 5 amps so far.
I have set the bias and DC offset on all but none were radically out of spec.

I'd need your guidance on getting the replacement done. Is it worth it?

Hummm, well if you have to pay a tech to do the work your asking about, in todays market
I'd have to say NO. The last 555 Hoppes Brain did cost $1,210

Hoppe's Brain

Audio circuit board kits, for Adcom and otherwise. High-end audio repair.

hoppesbrain.com

For those with a deep Adcom love affair, along with deep pockets, fine.
But if I was starting from point A today, I'd probably buy a Buckeye 8ch 350 wpc Hypex amp
for under $2200 and be ready to rock.

Buckeye Amps

Buckeye Amps utilizes the most advanced audio amplifier technologies available. Authorized seller for Hypex and Purifi Class D amplifiers. Based in the US. Free shipping and worldwide service!

www.buckeyeamp.com

Sound? The Pass designed GFA 5x5 line of amps are IMHO totally transparent, as are the new Hypex amps.
While doing bias controlled DBT's, I wouldn't expect you to be able hear any difference between them while
being run within their linear power ranges.
Best of luck and I hope you find your path to amp nirvana.
May the 4th be with you.

 

[Doodski]

the left channel has a lot of constant hum/noise.

Usually in this situation it could be bad solder, bad grounds or bad capacitors. All of those would be addressed in a repair.

When switched off, it makes crackling sound only in the left channel.

Same reasons as above^^^.

For peace of mind, I want to overhaul it once so that it does not trouble me for the next couple of decades atleast.

If you replace capacitors then you would need good quality caps for a long term repair to succeed.

 

[bhu1kaura]

For now, I'll focus on getting rid of the hum/noise. I know a technician working at a Denon service centre. Hope this should be a straight forward issue for him to resolve.

Thanks for helping out!

Cheers!
Bhuwan

 

[Sal1950]

For now, I'll focus on getting rid of the hum/noise. I know a technician working at a Denon service centre. Hope this should be a straight forward issue for him to resolve.

Thanks for helping out!

Cheers!
Bhuwan

Yep, that should be fairly easy to trace back.
Good Luck

 

[jtrygstad]

Speaking of Adcom, Hoppe's Brain, etc., I recently upgraded the power supply in my old Adcom GFA-545ii. I hadn't really done any significant kit-work since Heath kits in the 1960s. Turned out well and did my first bias adjustments using Brian's method. While I was at it, got rid of the 16ga zip cord power and replaced with a nice three-wire shielded Chinese cable for about $23 from Amazon, upgraded the speaker terminals and RCA inputs. Absolutely silent of any noise. At first I thought I screwed something up when I turned on the amp the first time since no startup pops, hum, etc. Glad for Hoppe's kit and the venerable Adcom. Likewise for the GFA-555 (this thread focus) Hoppe's has several nice kits to preserve these great amps.

 

[jtrygstad]

Adcom GFA-545 project photos.

 

[Sal1950]

Adcom GFA-545 project photos.

Nice amp.
The GFA-545 II's were always one of my favorites. I'm using 3 of them for my 5 base channels and 2 GFA-535 II's for
the Atmos height channels. Nelson Pass designed them before he got caught up in the "distortion tuned" world of high end amps. Too bad, these were guys were very clean, transparent, low noise designs that are hard to beat at any cost.
JMHO.

 

[Andersonix]

Nelson Pass designed them before he got caught up in the "distortion tuned" world of high end amps. Too bad, these were guys were very clean, transparent, low noise designs that are hard to beat at any cost.

What? Each Adcom 5x5 is beatable by each later (also Pass-designed) Adcom 5x00 just by virtue of being all-mosfet amps.

 

[Sal1950]

What? Each Adcom 5x5 is beatable by each later (also Pass-designed) Adcom 5x00 just by virtue of being all-mosfet amps.

The first 5x00 mosfet line was the last Adcoms Nelson did any design work on.
Just an FYI

 

[Gorgonzola]

I've been running this original version of the amp since new -(1985 to 90 perhaps?) and wanted to ask a few questions.
First to it's continued safe use given it's age and concern for some very nice speakers I would hate to see harmed.
Second is simply might there be possible sonic improvements to be had from other amplifiers? I don't hold any particular faults with the amp, but nor have I used anything else in years, plus I wouldn't mind having a bit more headroom occasionally available for the larger of the speaker sets.
Thanks

I briefly owned a GFA-555II 10-12 years ago, (not the 555). It was built like a tank and was stable at 2 ohms. It sounded very good, not at all harsh but a bit dark; not quite as transparent perhaps as amps I've owned since -- as it seems to me (subjective). Kind of sorry I sold it.

Adcom still makes makes an updated version of the GFA-555II called the GFA-555ms which, at US$1400, is probably quite a bargain. OTOH, personally I get one of the newer class D amps -- lighter, cooling-running, and a bit more transparent to some ears at least. If you feel you really need more power that your 555, for consideration I'd suggest this Apollon Audio AS1200.

 

[SIY]

I briefly owned a GFA-555II 10-12 years ago, (not the 555). It was built like a tank and was stable at 2 ohms. It sounded very good, not at all harsh but a bit dark; not quite as transparent perhaps as amps I've owned since -- as it seems to me (subjective). Kind of sorry I sold it.

Adcom still makes makes an updated version of the GFA-555II called the GFA-555ms which, at US$1400, is probably quite a bargain.

Black faceplate = dark sound

 

[Gorgonzola]

Black faceplate = dark sound

Haha!! Sure, maybe it was the faceplate.

Actually back in the day the word I suggested was "earthy"; a member on another forum at the time thought it was a very apt description.