GFA-555ii - Need some advice on bias and static. Gurus?
Answers
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The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * custom 5B on a system for my Dad * Ye Olde college stereo in the garage -
I can hear your meme- Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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He's saying "Masking tape" isn't he.Gustard X26 Pro DAC
Belles 21A Pre modded with Mundorf Supreme caps
B&K M200 Sonata monoblocks refreshed and upgraded
Polk SDA 1C's modded / 1000Va Dreadnaught
Wireworld Silver Eclipse IC's and speaker cables
Harman Kardon T65C w/Grado Gold. (Don't laugh. It sounds great!)
There is about a 5% genetic difference between apes and men …but that difference is the difference between throwing your own poo when you are annoyed …and Einstein, Shakespeare and Miss January. by Dr. Sardonicus -
Too bad you didn't run across some of my comments from years ago on my pair of 555 II's. In a nutshell I had a pair and one of them decided to put out 6 volts dc to a vintage infinity I had at the time. With no dc protection the amp could've started a fire had I not been home. I walked away from both of them after that fiasco and considered myself lucky. I've pretty much given up mentioning this as some clown will always want to argue and say how his magnificent adcom has been running fine all these years and he doesn't see an issue. Well I didn't see an issue with mine either........until it happened.
I agree with what's already been said; don't use it and don't spend $1500 on repairing an old adcom. It's a tough lesson to learn and I know how you feel if it's any solace. If one plays the vintage stereo game long enough things like this do happen. -
Would a 1.5A inline speaker fuse have protected the speakers in this case? I have read that it is not all that difficult for a techy person to install a DC protection circuit in these vintage amps. Maybe that should be considered as necessary in this case, even if all the caps and input transistors are swapped out for new ones.George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
@plastic_avatar I would say installing one of these is non-negotiable for you if you want to use this Adcom amp that has no protection in the future. This would also cure any turn on/off thump issues at the same time. He made one mistake that was pointed out in the comments section, which is that you have to connect the ground up to it:
Installing an Internal Protection Relay in an Adcom GFA 555
https://www.youtube.com/watch?v=Jz2R5dzkEhY
Here is the module that he used but it says it doesn't ship to the United States.......always sumthin' right??? 😡
https://www.ebay.co.uk/itm/264680770570
Also, he stated in the comments section that the Adcom 555 has bleeder resistors across the filter capacitors and therefore they discharge pretty rapidly. Needs to be verified.Post edited by Gardenstater onGeorge / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
@plastic_avatar This appears to be the same one and it ships free to US
https://www.ebay.com/itm/125254850460George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * custom 5B on a system for my Dad * Ye Olde college stereo in the garage
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George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
Send it!
Brian
One-owner Polk Audio RTA 15TL speakers refreshed w/ Sonicap, Vishay/Mills and Cardas components by "pitdogg2," "xschop" billet tweeter plates and BH5 | Stereo REL Acoustics T/5x subwoofers w/ Bassline Blue cables | Rogue Audio Cronus Magnum III integrated tube amp | Technics SL-1210G turntable w/ Ortofon 2M Black LVB 250 MM cart | Sony CDP-508ESD CD player (as a transport) | LampizatOr Baltic 4 tube DAC | Nordost & DH Labs cables/interconnects | APC H15 Power Conditioner | GIK Acoustics room treatments | Degritter RCM -
Don't take experimental gene therapies from known eugenicists.
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The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * custom 5B on a system for my Dad * Ye Olde college stereo in the garage -
@motorstereo Thanks for the insight. I can't believe I didn't dig up your thread. The Algorithm is fickle.
If I lost the money on it... I'm not distraught. A little irritated that I made a bad purchase, of course. Though... I'm stubborn and hate giving up on a project =(
I appreciate you chiming in, it does give me a little solace.
Going back to my AX-596 as an amp isn't terrible, but... now that I know what I'm missing =[The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * custom 5B on a system for my Dad * Ye Olde college stereo in the garage -
I couldn't find any good memes (lol) but maybe this video might be useful. He cleans out the amp with a shop vac (good technique), checks DC offset (got anomalous reading that turned out to not occur when playing music...weird), checks and adjusts the bias voltage, and checks the temps inside the amp with an Infrared camera (parts do run on the high side with this amp).
https://www.youtube.com/watch?v=R-3MPSs3K_I George / NJ
Polk 7B main speakers, std. mods+ (1979, orig owner)
Martin Logan Dynamo sub w/6ft 14awg Power Cord
Onkyo A-8017 integrated
Logitech Squeezebox Touch Streamer w/EDO applet
iFi nano iDSD DAC
iPurifier3
iDefender w/ iPower PS
Custom Steve Wilson 1m UPOCC Interconnect
iFi Mercury 0.5m OFHC continuous cast copper USB cable
Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
Custom Vibration Isolation Speaker Stands and Sub Platform -
Troubleshooting is usually more difficult than upgrading or just replacing capacitors, that's why most companies that upgrade these amplifiers want a properly working amplifier. The mk2 is also a little more complex than the mk1, it has a triple Darlington output stage and a DC servo circuit if memory serves me right.
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Decided to attempt the bare minimum and check/adjust the bias. Got some clips for the meter, put on some rubber gloves, and poked around.
Output at terminals was near zero,
The left channel read 4mv at power on. Settled at 10.1 after 20 minutes.
The right channel read 6mv and then down to 4mv at power on. It settled at 13.7 after 20 minutes, but I got it to a solid 10 w/ the bias screw.
Tried to get the left channel to an even 10, but it wouldn't give me that .1. It just jumped between 9.4 and 10.7 until I finally got it to settle back at 10.1. It then surprised me and ticked back a point to 10.
The large caps say they need replaced (per a suggestion above). On each channel, powered on, one bounced around and measured (I can't remember the decimal point...) 200 to 260 and the other 175'ish. Regardless of my sleepy memory, the caps were way off from each other, but matched on each side (1 high, 1 low). If I understand correctly.
I was just looking to check/adjust the bias and do a quick touch-and-go on the big caps to see if they measured the same. They did not.
Unit still sounds better than my others.
Future stop on the 'What next on the dot-it-myself train?'
4 new big 'ol caps?
The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * custom 5B on a system for my Dad * Ye Olde college stereo in the garage -
Awesome. What size are the big supply caps? Open a Mouser account and replace all the electrolytics while you're in there.Don't take experimental gene therapies from known eugenicists.
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As long as the DC stays put, and I don't have a @motorstereo type meltdown... Gah. SUCKS. It does suck. I feel like I'm rolling the dice when/if I use it. Which, to a point, I guess I am =(
Everything here and everything I read points to:
- check DC at terminals (done, no problem there)
- check and adjust bias (done, thump is less on left, about the same (anecdotally) on right as before)
- and caps, caps, caps!
There are other things that could be wrong, and taking to a servicer is the best option for ye olde oscilliscope'ing and expert opinion, but most-times, other than those 3 bullets, the other stuff is rare.
A soft start and speaker protection relay are available, though there's debate on the protection circuit and sound quality.
So far, the available, within 2 hours of me servicers are a no go =( And one used to do Adcoms on the regular.
My posts tend to have a theme, don't they?
'I have X, but Y doesn't work, so can I do Z? Ah, yes, I can do A, or have someone who knows better do A... but what about B? Can I do B?... Ah, not the best idea... Right. But I'm out of choices... so maybe I'll treat it as a learning experience?'
I've been extremely lucky, so far.
But Christmas is coming, so priorities are changing.
=|The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * custom 5B on a system for my Dad * Ye Olde college stereo in the garage -
Too bad we don't have a viewed count here
Views: 20
Views by OP: 19
Gustard X26 Pro DAC
Belles 21A Pre modded with Mundorf Supreme caps
B&K M200 Sonata monoblocks refreshed and upgraded
Polk SDA 1C's modded / 1000Va Dreadnaught
Wireworld Silver Eclipse IC's and speaker cables
Harman Kardon T65C w/Grado Gold. (Don't laugh. It sounds great!)
There is about a 5% genetic difference between apes and men …but that difference is the difference between throwing your own poo when you are annoyed …and Einstein, Shakespeare and Miss January. by Dr. Sardonicus -
Awesome. What size are the big supply caps? Open a Mouser account and replace all the electrolytics while you're in there.
The big supply caps are 15,000uf, but very rarely go bad, it's usually all the small electrolytic caps that need replacement. The only two adcom models that had bad caps were the 565 and the 585. -
The big supply caps are 15,000uf, but very rarely go bad, it's usually all the small electrolytic caps...
I'll take it back to the table and hit what I can with the meter to see how things measure.
Everything should measure the same as their counterparts on the other channel, at rest/no input, correct?
The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * custom 5B on a system for my Dad * Ye Olde college stereo in the garage -
They do go bad. My good friend had to have them all replaced. The cost was about $300 in the 90's. The amp was bought new and never turn off, he got a good 25-30 out of them.Awesome. What size are the big supply caps? Open a Mouser account and replace all the electrolytics while you're in there.
The big supply caps are 15,000uf, but very rarely go bad, it's usually all the small electrolytic caps that need replacement. The only two adcom models that had bad caps were the 565 and the 585.
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They do go bad. My good friend had to have them all replaced. The cost was about $300 in the 90's. The amp was bought new and never turn off, he got a good 25-30 out of them.Awesome. What size are the big supply caps? Open a Mouser account and replace all the electrolytics while you're in there.
The big supply caps are 15,000uf, but very rarely go bad, it's usually all the small electrolytic caps that need replacement. The only two adcom models that had bad caps were the 565 and the 585.
I'm not saying that they never go bad, but they generally don't.
https://www.youtube.com/watch?v=iAeksZp0Fio
