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Peter, I thoroughly enjoyed your opinion on the adcom amplifiers. I would love to talk to the technician in LA you mentioned. Thank you
 

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I have a GFA-555 and a GFA-555ii. I LOVE these amps!! Thinking of picking up another GFA-555ii. They will run all my subs. 2 15s, and hopefully soon 4 12s for near-field.

Anyone know what the fan mod is for the Adcoms? I was just going to run 120mm computer fans across the cooling fins.

I also have a Emotiva UPA-5 to run my HT. It doesn't have the horsepower as the Adcoms do, but still a great amp to run the HT speakers.

Edit: I also had an Outlaw amp. 5X100. No beuno for power for me. Sounded good, just not enough power.
 

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Discussion Starter #44
So, the guy that turned you on to Sony ES got no credit for the sale?
He was happy to finally get me into a receiver so I stopped bugging him. But to make up for no commission on the receiver I bought expensive speaker wire which has a HUGE markup and I bought a Blu-Ray player and finally just a month ago bought new speakers at a big discount, but he still made some money on me with those too. He likes helping me out and I like giving him my business.
 

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It's nice to see these older Adcom components getting treated nicely. We need more service guys around as this is how it was in the good old days. I sold my 555, passed a matching stereo preamp on to my son (he still uses it).
I kept an Adcom five channel amp for future use...GFP-7700 THX 150x5 ...great amp...still have their second or third generation Pro-pro...it needs a rubber volume cover as the granddaughter borrowed it.
 

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Anyone know what the fan mod is for the Adcoms? I was just going to run 120mm computer fans across the cooling fins.

GFA 555II amp power (watts) - power consumption (VA):

200w x 2 @ 8 ohms - 675 VA

350w x 2 @ 4 ohms - 1180 VA

600w x 1 @ 8 ohms - 1320 VA (bridged)

850w x 1 @ 4 ohms - 1500 VA (bridged/fan mod)

Owner's Manual (page 7):

"Although the GFA 555II can generate a substantially greater amount of power in the bridged mono mode than when it is in its normal stereo mode, it requires the use of loudspeakers the nominal impedance of which does not drop below 4-ohms. It is not recommended that the GFA 555II be used in the bridged mono mode into loudspeakers, or multiple loudspeaker loads, which drop in value substantially below 4-ohms. Otherwise you may trigger the THERMAL PROTECTION or blow one of the DC RAIL FUSES"

"A little known fact is that whenever any amplifier is operated in the bridged mode, the load is "split" between the two amplifiers in the bridged configuration. Therefore, an 8-ohm speaker will be seen by the amplifier as if it were a 4-ohm load; a 4-ohm loudspeaker load will be seen by the amplifier as a 2-ohm load."


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That being said in the Owner's Manual, I have run three of my GFA 555II's bridged without fans on a pair of Martin Logan Requests and a Martin Logan Theater for many years. The 'stats impedance can dip temporarily to 2 ohms and my Adcoms have never blown a fuse.

The Series II GFA 555's had larger heat sinks than the Series I GFA 555's as well a bit more complicated Darlington output stage whose only advantage was allowing it to be a bit more stable driving extremely low impedance loads (less than 2 ohms) which is not typical of traditional speakers except ribbons or electrostatic.

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There is a secondary rail on the main transformer that was originally dedicated for the use of an optional fan motor. This rail has 22V AC power supply but I have never seen the need to use it for the fan mod.

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However, a well know thermal problem of this amplifier is the overheating of VAS transistors (located in the center top directly behind the RCA input jacks on the rear panel). Adcom should have mounted heatsinks on VAS transistors. Without heatsink the transistors of VAS stage are very hot. The overheating of these transistors are demonstrated also by the browning of solder side of PCB.

A GFA 555 II modification to solve this problem is to make a custom heatsink for VAS and relative current source transistors. With this mod the temperature of these transistor remain around 51 °C, a very good result. These transistors can then work in their Safe Operating Area, do not regenerate a temperature dependent noise and have more margin of stability.















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If you were to simply incorporate a computer fan instead of doing the heat sink modification, mounting it directly over the VAS and relative current source transistors (rear center top) to dissipate the heat would be your best bet. This also matches what John Atkinson observed about the Adcom GFA-555 Mk.II with fan option in Stereophile October 1990 (Vol.13 No.10):

"Superficially, the new '555 appears identical to the old. A closer look, however, reveals a greater number of cooling vents in the case and a cooling fan lying just under the top plate. (This fan, a $100 option, is triggered by heatsink temperature and didn't turn on during my auditioning"

http://www.stereophile.com/content/adcom-gfa-555-power-amplifier-john-atkinson-1990#zrBqcIwohgbAi0Rc.97


The heat sink fins on the back panel are already very efficient at drawing heat from the output stage which consists of two sets of 4 parallel transistors for each channel.



 

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Currently I have my 555 ii running 2 15s and hardly gets warm. My 1st gen 555 is in the shop getting a look over. I had it hooked up and it got really hot and wouldn't work in bridge mode. Hope it doesn't take too much money to repair!
 

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I have an Adcom GFA-555 amp. It's a 2 channel 200 WPC RMS AMP. I've never had any problems with it until last week with it was hit by lightening. I noticed on Adcom's website they brought back the GFA-555 now called the GFA-555se. Looks the same on the outside and they said the inside has been updated. You can buy a used GFA-555 amp on eBay for $200-300. Is a new one really worth $1299 or are there better amps out there? What I like about the Adcom amp is that what you put into it, it puts back out. If you hook it to a Yamaha receiver you get that Yamaha sound. If you hook it to an old Harman Kardon receiver you get the warmer HK sound. The Adcom amp doesn't really alter the sound. But again really, is it worth $1299 or what else should I be looking at either to get a better AMP for $1299 or an equal amp for less money. Thanks in advance!!
There may be better, but all equipment has it's own sonic signature, if you value a neutral sound stick with the Adcom. I would avoid used, power supplies don't age well in electronics as they get older. If you get a new Adcom make sure it still has the neutral sound you like.
 

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There may be better, but all equipment has it's own sonic signature, if you value a neutral sound stick with the Adcom. I would avoid used, power supplies don't age well in electronics as they get older. If you get a new Adcom make sure it still has the neutral sound you like.


All of these vintage amplifiers sound so good specifically because they are very simple designs that have an enormous power supply and tremendous amounts of capacitance reserve power on tap. Their parts can wear out and need replacing, but once swapped out with new, they are as good as the day they left the factory. Most of the time you change the capacitors, update a few other parts and check the bias.

With the possible exception of Sanders Sound, you just can't buy an amplifier with power supplies as beefy as they used to make them. Certainly not between $500 - $1k which are used prices a fraction of what these amps sold for new (plus accounting for pre-inflation dollars).

In today's market, adding a vintage amp (properly re-capped and updated) to the pre-out's on your receiver will yield the greatest sonic improvement. A good example is the Onkyo TX-NR3030 at $2,400 list. Unless you want to buy a new AVR to get the latest Dolby Atmos features, for the same amount of cash you could add 3-4 vintage amps to your current receiver (using just it's preamp section) and have much more power to drive your home theater.

Over the years I've collected and maintained my vintage amplifiers. All I update every few years is the processor to keep up with the latest codex's and copy protection.

This gets you the best of both worlds: old world build quality/power and new world sound. :)


2015
Onkyo TX-NR3030

This is supposed to power 11 channels at 135 watts per channels

Look at the size of the transformers and capacitors compared to the amps below







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1985 / 1990
Adcom GFA 555




1994
Carver Sunfire Signature



Haffler DH500




1976 / 1979
Haffler Dh200/220




1980
Krell KSA100 MkII




1979
Mark Levinson ML2




1968
McIntosh MC3500



1999
Rotel 991



2000
Rotel 1090




1975
Threshold T800




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2012
Sanders Magtech

http://sanderssoundsystems.com/products/amplifiers/magtech-amp
http://www.stereotimes.com/amp051412.shtml


 

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Hi Peter, I'd also love to get the contact info for your repair guy in Los Angeles who worked on your Adcom amps. I know this thread is a few years old but I have several GFA 555's and 535's I'd love to get serviced. Although I'm in the Bay Area, I'm down in SoCal pretty regularly so I can probably drop them off rather than ship 'em. Thanks!
 

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Hi Peter, I'd also love to get the contact info for your repair guy in Los Angeles who worked on your Adcom amps. I know this thread is a few years old but I have several GFA 555's and 535's I'd love to get serviced. Although I'm in the Bay Area, I'm down in SoCal pretty regularly so I can probably drop them off rather than ship 'em. Thanks!
It's glad to see the thread that I started is still getting used. My GFA-555 that was rebuilt is still doing a great job. I also had the chance to purchase another GFA-555 and it's in the closet as a spare. My local repair shop said that the GFA-555 is better than the GFA-555II and on Ebay it seems that the GFA-555 is selling for more than a 555II, so my question to all of you is, what is the difference between a 555 and a 555II?

I've upgraded my system a couple times since I've posted on here. I went from the Sony ES STR-ZA3000ES to the Sony ES STR-ZA5000ES because I wanted ATMOS. It's still a great receiver but I actually liked the 3000ES better. I also have a flagship Yamaha sitting in the box that I am eager to try out. I've been getting major electrical work done to the new house so currently I'm not using anything. In a couple weeks I should be back up and running.

If anyone is wanting a repair shop with a good reputation, my GFA-555 is still going strong for the $85 I paid to fix it. Look up "Speaker Workshop" on Facebook. He's in Fort Wayne, Indiana. I've taken other products to him to fix, difficult fixes, and he's always done a great job.
 

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I have an Adcom GFA-555 amp. It's a 2 channel 200 WPC RMS AMP. I've never had any problems with it until last week with it was hit by lightening. I noticed on Adcom's website they brought back the GFA-555 now called the GFA-555se. Looks the same on the outside and they said the inside has been updated. You can buy a used GFA-555 amp on eBay for $200-300. Is a new one really worth $1299 or are there better amps out there? What I like about the Adcom amp is that what you put into it, it puts back out. If you hook it to a Yamaha receiver you get that Yamaha sound. If you hook it to an old Harman Kardon receiver you get the warmer HK sound. The Adcom amp doesn't really alter the sound. But again really, is it worth $1299 or what else should I be looking at either to get a better AMP for $1299 or an equal amp for less money. Thanks in advance!!
The original Adcom GFA-555 was designed by Nelson Pass. If you're not familiar with the work of Nelson Pass, he's something of a living legend in the world of audio amplifiers and was/is the guy behind past companies Threshold, Forté, and the Nakamichi Stasis amplifiers. Pass worked at the old ESS speaker company and holds 6 patents related to magneplanar speakers. Pass built a corona wind or ion speaker that makes sound through high voltage discharge, no moving parts. His current companies Pass Labs and First Watt produce very highly regarded products today. Pass is also very active and accessible offering support to the DIY community for those wishing to build their own.

The GFA-555 was a bench mark product in both design and price point; a very highly regarded product that received great reviews. It can hold its own with units cost substantially more and was capable of driving speaker loads as low as 1Ω.

The Adcom of today is not the same company. Adcom, like so many well respected brands in audio and consumer electrons has been sold. Adcom is now owned by Everest World Company Ltd., of Bangkok, Thailand. I know nothing about the Everest World Company, the new Adcom or their products other than they make use of the old Adcom reputation in selling their new products. There are anecdotal claims of poor customer service to be found if you do a search.

If it were me, I'd take the GAF-555 to a competent repair shop and have it fixed. It was and remains to be a very good amplifier.
 

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Discussion Starter #60
The original Adcom GFA-555 was designed by Nelson Pass. If you're not familiar with the work of Nelson Pass, he's something of a living legend in the world of audio amplifiers and was/is the guy behind past companies Threshold, Forté, and the Nakamichi Stasis amplifiers. Pass worked at the old ESS speaker company and holds 6 patents related to magneplanar speakers. Pass built a corona wind or ion speaker that makes sound through high voltage discharge, no moving parts. His current companies Pass Labs and First Watt produce very highly regarded products today. Pass is also very active and accessible offering support to the DIY community for those wishing to build their own.

The GFA-555 was a bench mark product in both design and price point; a very highly regarded product that received great reviews. It can hold its own with units cost substantially more and was capable of driving speaker loads as low as 1Ω.

The Adcom of today is not the same company. Adcom, like so many well respected brands in audio and consumer electrons has been sold. Adcom is now owned by Everest World Company Ltd., of Bangkok, Thailand. I know nothing about the Everest World Company, the new Adcom or their products other than they make use of the old Adcom reputation in selling their new products. There are anecdotal claims of poor customer service to be found if you do a search.

If it were me, I'd take the GAF-555 to a competent repair shop and have it fixed. It was and remains to be a very good amplifier.
My post from last night explains that I did have the GFA-555 repaired for $85 quite a long time ago and it still is running great. I also bought another GFA-555 as a backup and it's in my closet. I was wondering though, what is the difference between the 555 and the 555II? I know all about Nelson Pass. Was he not involved in the series II? For some reason the 555 sells for more than a 555II and my repair shop said the 555 is a better amp than the 555II but I have no idea why. As far as the newer 555se, I've seen a lot of them for sale used in different places on the internet so my guess is that they are junk.
 
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