@anatech: Thank you so much for your help. I definitely want to learn more and become an educated audiophile like many on these forums. It was truly a pleasure to introduce myself here over a year ago and learn the little bit that you all taught me in fixing my own amps. After which I was bombarded with many questions and "fix my amp" propositions. I initially declined all of them because I did not feel confident enough to tackle them. With more knowledge and experience I can confidently do it, but you're right, I do need more basic knowledge and proficiency, especially regarding the fashion in which I go about diagnosing and fixing amps!
I can recall one man who contacted me directly asking for advice, I of course referred him to diyAudio.com and also this very thread but he insisted on asking me for advice over email even after I explained to him that I was not equipped to answer half of his questions with any assurance of accuracy or reliability. He presented with several specific problems and asked me why I chose to replace and upgrade specific components in my amps. He told me that he needed some guidance in fixing his own amps for his own use, I only learned that he lied to me when I searched eBay's listings and found that same guy peddling repaired 565s and I thought to myself, this guy didn't know his *** from his elbow and he is selling repaired 565s??? He didn't know what the purpose or function of the AC input board was and the purpose of the giant ceramic resistor to delay the inrush current on powerup. I wasn't upset about him profiting off of my advice. What truly upset me though is that he was selling 565s and repaired and upgraded when he did a mediocre job and obviously didn't understand the amps nearly as much as I do (and I admit I have a very loose grasp on these amps). I was very upset but didn't say anything to him. He's still doing it with other amps too.
So I do understand your concerns regarding my interest in providing the service to others. The distinction between me and the eBay guy is that I go about this purely as a hobby in which knowledge that I gain from my interactions here is openly shared and always quoted accurately, referenced, and NEVER plagiarized. I don't claim to have the answers but share the answers that I am blessed to have been given by you guys. I don't steal the help that I get and try to profit off of it (like that guy), and I tell anyone I meet about this website and this very thread. My interest is solely in assisting other users--in whatever way i can--to bring dignity back to a 20 year old beautiful amplifier by breathing life back into it!
With that said I'm going to make an effort to invest in proper test equipment in addition to learning some more of the basic fundamentals and safe and sensible diagnosing procedures. I do have a new DMM with quite a lot of features including a diode tester which is serving me well, but I want to build a custom jig to test the Darlington transistors in the 565, which I am told is tricky to do!
Regarding replacing old components, my philosophy has always been that changing out old stuff with new ones can increase reliability. What are your thoughts on this? In an amplifier setting, can replacing old parts (i.e. rectifier, filter caps, other electrolytics, etc.) introduce significant problems rather than reduce the possibility of catastrophic failure in a high-stress (temp, current, etc...) electrical environment?
I can recall one man who contacted me directly asking for advice, I of course referred him to diyAudio.com and also this very thread but he insisted on asking me for advice over email even after I explained to him that I was not equipped to answer half of his questions with any assurance of accuracy or reliability. He presented with several specific problems and asked me why I chose to replace and upgrade specific components in my amps. He told me that he needed some guidance in fixing his own amps for his own use, I only learned that he lied to me when I searched eBay's listings and found that same guy peddling repaired 565s and I thought to myself, this guy didn't know his *** from his elbow and he is selling repaired 565s??? He didn't know what the purpose or function of the AC input board was and the purpose of the giant ceramic resistor to delay the inrush current on powerup. I wasn't upset about him profiting off of my advice. What truly upset me though is that he was selling 565s and repaired and upgraded when he did a mediocre job and obviously didn't understand the amps nearly as much as I do (and I admit I have a very loose grasp on these amps). I was very upset but didn't say anything to him. He's still doing it with other amps too.
So I do understand your concerns regarding my interest in providing the service to others. The distinction between me and the eBay guy is that I go about this purely as a hobby in which knowledge that I gain from my interactions here is openly shared and always quoted accurately, referenced, and NEVER plagiarized. I don't claim to have the answers but share the answers that I am blessed to have been given by you guys. I don't steal the help that I get and try to profit off of it (like that guy), and I tell anyone I meet about this website and this very thread. My interest is solely in assisting other users--in whatever way i can--to bring dignity back to a 20 year old beautiful amplifier by breathing life back into it!
With that said I'm going to make an effort to invest in proper test equipment in addition to learning some more of the basic fundamentals and safe and sensible diagnosing procedures. I do have a new DMM with quite a lot of features including a diode tester which is serving me well, but I want to build a custom jig to test the Darlington transistors in the 565, which I am told is tricky to do!
Regarding replacing old components, my philosophy has always been that changing out old stuff with new ones can increase reliability. What are your thoughts on this? In an amplifier setting, can replacing old parts (i.e. rectifier, filter caps, other electrolytics, etc.) introduce significant problems rather than reduce the possibility of catastrophic failure in a high-stress (temp, current, etc...) electrical environment?
Hi a.wayne,
Thank you.
Hi mjraudio,
I am more concerned that when anyone pays for work, that it is done properly and fairly. There are legal implications when you work on someone else's equipment if you make an error and the fact that you are not formally trained comes to light. You do not want to be in that position.
I do know you mean well, unlike the Eeekbay person. In fact, I do know that most stores employ what I would call "hackers" for service and Eeekbay people are worse. It's like the wild west out there. Sadly, most "hackers" pick up their information from web sites such as this. Most of these people advertise their work as modifiers of equipment. I've often seen speaker wire permanently connected and used as AC cord, of course with "hospital grade plugs". Kinda illegal.
I do encourage you to learn and experiment, but please on your own equipment. You will always have a lineup of people wanting you to service their stuff.
-Chris
Thank you.
Hi mjraudio,
I am more concerned that when anyone pays for work, that it is done properly and fairly. There are legal implications when you work on someone else's equipment if you make an error and the fact that you are not formally trained comes to light. You do not want to be in that position.
I do know you mean well, unlike the Eeekbay person. In fact, I do know that most stores employ what I would call "hackers" for service and Eeekbay people are worse. It's like the wild west out there. Sadly, most "hackers" pick up their information from web sites such as this. Most of these people advertise their work as modifiers of equipment. I've often seen speaker wire permanently connected and used as AC cord, of course with "hospital grade plugs". Kinda illegal.
I do encourage you to learn and experiment, but please on your own equipment. You will always have a lineup of people wanting you to service their stuff.
-Chris
Re-re-re-hijack? Half-Dead GFA 565 Monoblock
Hello again, DIY Audio folks.
It's been nearly a year since my last post, and I return, soldering iron in hand, to beg once again for advice.
I have decided to post on this thread first, as it has remained lively, as it has been hijacked a few times since its inception, and as it has helped me a great deal in fixing my amp already. If this is a bad place for me to post, I will repost a new thread to the Solid State board.
The story so far:
I run (ran) four GFA 565's, driving two Infinity QLS-1's. One day last year, I decided to check my DC offset after reading this thread. Much to my surprise, I was pushing 27VDC from one amp, with all others within spec. Upon opening all of them, I discovered the bad amp was fitted with the notorious "Elna" electrolytics, while the others were not.
After a series of false starts, I procured an US cleaner, stripped and cleaned my input board properly, found some bad components, put it all back together, had an excellent-working amp, and was very pleased with myself .
All was well in paradise until last week, when my wife (whom I love very much) decided she wanted to touch up some paint on the walls, and that in order to do this she had to move the QLS-1's. Well, the speaker wires run under the floor, coming up just behind the speakers (which have to sit about two feet from the walls for optimum sound), so as to be as safe from injury as possible, the QLS-1's are six feet tall and weigh 150 pounds each, and my wife is not the most attentive person to her immediate surroundings. She slid the speakers across the floor, pulling one set of wires off of the posts. She says "the music wasn't playing" at the time, which means the amps were on (impolitic to interrogate one's wife after losing one's temper and acting like an a-s already).
Now the amp that fed those wires don't work no more
.
What I get, subjectively, is a low-gain grainy, tinny, clipped-sounding signal, which reminds me of blown output transistors past.
Other findings:
• All 3 fuses look and test okay
• Both input-board green LED's light up
• No bad smells, noises, or burned spots
• Bias 0.1mV, steady
• DC offset: 6V at turn-on, down to 0 over a minute,
then up to -70mV, then back past 0 to 80mV, etc.,
oscillating with a period of about 2 minutes
• Resistances:
Power input (chassis) ground to RCA ring -or- to Speaker Neg: ∞
RCA Input ring to Speaker Neg: ~20mΩ
Fortunately, you can still run a pair of QLS-1's on TWO GFA-555's
, but I want ALL my babies to be working .
So, though I can claim to have half a brain, I am not a tech or an EE, and am not sure how to approach this. Any suggestions on where to start or what might be the problem?
Thanks,
- Eric
Hello again, DIY Audio folks.
It's been nearly a year since my last post, and I return, soldering iron in hand, to beg once again for advice.
I have decided to post on this thread first, as it has remained lively, as it has been hijacked a few times since its inception, and as it has helped me a great deal in fixing my amp already. If this is a bad place for me to post, I will repost a new thread to the Solid State board.
The story so far:
I run (ran) four GFA 565's, driving two Infinity QLS-1's. One day last year, I decided to check my DC offset after reading this thread. Much to my surprise, I was pushing 27VDC from one amp, with all others within spec. Upon opening all of them, I discovered the bad amp was fitted with the notorious "Elna" electrolytics, while the others were not.
After a series of false starts, I procured an US cleaner, stripped and cleaned my input board properly, found some bad components, put it all back together, had an excellent-working amp, and was very pleased with myself
. All was well in paradise until last week, when my wife (whom I love very much) decided she wanted to touch up some paint on the walls, and that in order to do this she had to move the QLS-1's. Well, the speaker wires run under the floor, coming up just behind the speakers (which have to sit about two feet from the walls for optimum sound), so as to be as safe from injury as possible, the QLS-1's are six feet tall and weigh 150 pounds each, and my wife is not the most attentive person to her immediate surroundings. She slid the speakers across the floor, pulling one set of wires off of the posts. She says "the music wasn't playing" at the time, which means the amps were on (impolitic to interrogate one's wife after losing one's temper and acting like an a-s already).
Now the amp that fed those wires don't work no more
.What I get, subjectively, is a low-gain grainy, tinny, clipped-sounding signal, which reminds me of blown output transistors past.
Other findings:
• All 3 fuses look and test okay
• Both input-board green LED's light up
• No bad smells, noises, or burned spots
• Bias 0.1mV, steady
• DC offset: 6V at turn-on, down to 0 over a minute,
then up to -70mV, then back past 0 to 80mV, etc.,
oscillating with a period of about 2 minutes
• Resistances:
Power input (chassis) ground to RCA ring -or- to Speaker Neg: ∞
RCA Input ring to Speaker Neg: ~20mΩ
Fortunately, you can still run a pair of QLS-1's on TWO GFA-555's
, but I want ALL my babies to be working .So, though I can claim to have half a brain, I am not a tech or an EE, and am not sure how to approach this. Any suggestions on where to start or what might be the problem?
Thanks,
- Eric
you're going to think this is an odd way to test an amp, but it works and tells you a few things about whether the output stage is working. with the amp on and no input, measure the offset and write it down. then switch to the diode check position on the meter and check across the output terminals again (yes with the amp on) the reading should be fairly close to the dc offset voltage reading from the first step (and the ohmmeter reading should be close to zero, not reading OL). it's ok if the ohmmeter reads slightly negatve too, since it's reading the resulting voltage when it pumps a current through the device under test. an amplifier with a decent damping factor should act almost like a short to an ohmmeter. swap the meter wires and verify that the reading is still close to zero. then remove the meter and shut off the amp and wait about 10 minutes, then reconnect the meter across the speaker terminals and verify that the amp in it's off state acts like an open circuit. these tests verify that 1) your speaker terminals are internally still connected to the output stage and that the output stage is intact (no open emitter resistors, etc). 2) your speaker terminals aren't shorted to ground inside the chassis.
i often use the ohmmeter test to verify that speaker relays are closing, etc.... in case you're wonsering, it's the negative feedback that corrects the amp for the dc current from the ohmmeter.
i often use the ohmmeter test to verify that speaker relays are closing, etc.... in case you're wonsering, it's the negative feedback that corrects the amp for the dc current from the ohmmeter.
Hi MDchanic,
What unclejed613 suggested will work. I must warn you that it places inexpensive meters in harms way. The same holds true for better meters, but they may survive due to their better protection.
No bias current means that the output stage has been shut down. Odd that you don't see any other warnings on the front panel. You do have damage for sure.
An amplifier does not have to be playing music to die when the speaker leads are shorted. When the short occurs, all the feedback for the amp has been removed. So, it's running open loop with a short across the output. Get the picture?
Another clue is your open reading between the RCA ground and chassis common. I would think you have lost a resistor or two for that fault. God luck, you have my wishes fir minimal damage.
It sounds like you run your stuff all the time. Is this what you are doing?
-Chris
What unclejed613 suggested will work. I must warn you that it places inexpensive meters in harms way. The same holds true for better meters, but they may survive due to their better protection.
No bias current means that the output stage has been shut down. Odd that you don't see any other warnings on the front panel. You do have damage for sure.
An amplifier does not have to be playing music to die when the speaker leads are shorted. When the short occurs, all the feedback for the amp has been removed. So, it's running open loop with a short across the output. Get the picture?
Another clue is your open reading between the RCA ground and chassis common. I would think you have lost a resistor or two for that fault. God luck, you have my wishes fir minimal damage.
It sounds like you run your stuff all the time. Is this what you are doing?
-Chris
Chris,
Thanks for responding.
No, I don't run the amps all the time, but if the system is going to be used it's usually turned on at the beginning of the day, and off at the end (four separate amp switches, plus the preamp, and perhaps a component or two - it gets tedious). I haven't yet gotten around to my overcomplicated one-switch plan (can't bear to pay over a hundred bucks for a fancy power controller that won't switch each amp to a separate outlet / breaker circuit).
No doubt my wife listened to a CD or two, forgot the system was on, and set about moving speakers around, then thought nothing of it when the wires pulled out, because the sound wasn't playing anyway.
Unclejed,
Thank you, too.
I checked the bias between the specified pins on the 2 opposite output boards.
Used to be 24mV. Not anymore.
I figured that might be a clue for someone experienced with these beasties.
Thanks again, guys, this site and your help are a phenomenal resource.
- Eric
Thanks for responding.
No, I don't run the amps all the time, but if the system is going to be used it's usually turned on at the beginning of the day, and off at the end (four separate amp switches, plus the preamp, and perhaps a component or two - it gets tedious). I haven't yet gotten around to my overcomplicated one-switch plan (can't bear to pay over a hundred bucks for a fancy power controller that won't switch each amp to a separate outlet / breaker circuit).
No doubt my wife listened to a CD or two, forgot the system was on, and set about moving speakers around, then thought nothing of it when the wires pulled out, because the sound wasn't playing anyway.
Unclejed,
Thank you, too.
I checked the bias between the specified pins on the 2 opposite output boards.
Used to be 24mV. Not anymore.
I figured that might be a clue for someone experienced with these beasties.
Thanks again, guys, this site and your help are a phenomenal resource.
- Eric
Okay, following unclejed's instructions, I tested the amp.
Offset wanders around for about five minutes, then settles down, oscillating around -140mV.
On diode setting, values are roughly the same, regardless of polarity.
With amp off, no continuity between + and - speaker terminals, so, yes, it acts like an open circuit when off.
Not to sound dumb, but, where does this leave me?
Thanks,
- Eric
Offset wanders around for about five minutes, then settles down, oscillating around -140mV.
On diode setting, values are roughly the same, regardless of polarity.
With amp off, no continuity between + and - speaker terminals, so, yes, it acts like an open circuit when off.
Not to sound dumb, but, where does this leave me?
Thanks,
- Eric
Stored GFA 565's
Greetings!
You can add me to the list of the Adcom 565 owners in need of repair.
This is a serious situation to say the least! The loss of a nice pair of amps is nothing compared to the damage they can cause.
I wish there was some way to alert all GFA 565 owners of this inevitable danger.
I bought mine brand new in the early 90’s and they were stored in the box for well over 10 years.
My high end audio mentor asked me to borrow them to help resolve an issue he was having with his system. ALL KRELL!
No problem, these amps are as pristine as ever. I barely used them. What are friends for?
Then the phone call came. Yea, it’s me. Your amps are junk. I hope my Krells are ok.
Then after some research, I tested the DC offset. OMG! 70+ VOLTS!
I’ve read this entire thread and I am very impressed. I am no expert in electrical engineering but I do have a good ear for sound and I can appreciate the time and effort spent on the restoration of the Adcom 565 monoblock.
Please let me share my thoughts and opinions. Thank you.
Anatech, you are a true inspiration to the hungry audio enthusiasts and electrical engineers that find joy in helping less fortunate audio freaks like me. You really know how to keep these guys honest. God bless!
MJR, all I can say is wow. You don’t give up, good is never good enough, as it should be.
I read somewhere, “If you don’t settle for anything but the best, you often get it”.
You are both very inspiring to those entering this field of work and thanks to all who participated in this thread. I wish I could have! Now I have to figure out what to do with these monsters.
Best Regards,
Tony
Greetings!
You can add me to the list of the Adcom 565 owners in need of repair.
This is a serious situation to say the least! The loss of a nice pair of amps is nothing compared to the damage they can cause.
I wish there was some way to alert all GFA 565 owners of this inevitable danger.
I bought mine brand new in the early 90’s and they were stored in the box for well over 10 years.
My high end audio mentor asked me to borrow them to help resolve an issue he was having with his system. ALL KRELL!
No problem, these amps are as pristine as ever. I barely used them. What are friends for?
Then the phone call came. Yea, it’s me. Your amps are junk. I hope my Krells are ok.
Then after some research, I tested the DC offset. OMG! 70+ VOLTS!
I’ve read this entire thread and I am very impressed. I am no expert in electrical engineering but I do have a good ear for sound and I can appreciate the time and effort spent on the restoration of the Adcom 565 monoblock.
Please let me share my thoughts and opinions. Thank you.
Anatech, you are a true inspiration to the hungry audio enthusiasts and electrical engineers that find joy in helping less fortunate audio freaks like me. You really know how to keep these guys honest. God bless!
MJR, all I can say is wow. You don’t give up, good is never good enough, as it should be.
I read somewhere, “If you don’t settle for anything but the best, you often get it”.
You are both very inspiring to those entering this field of work and thanks to all who participated in this thread. I wish I could have! Now I have to figure out what to do with these monsters.
Best Regards,
Tony
The Thread that Just Won't Die.
Greetings, all.
I am back, having done something really stupid, and wondering whether there might be a simple answer.
To pick up the story:
In April of 2009, I tested the amp as instructed, then ran into a dead end, and, not being trained in electronic troubleshooting, could go no further.
The system was working on two amps, and I got a new job that took some of my attention away from this problem, and, honestly, I was disgusted.
I watched eBay for replacement amps, and noticed the prices go up more or less as soon as I decided to buy one. There was no way I was going to spring for $500 for an amp, so I kept watching and waiting. It became a habit.
Finally a few weeks ago, and amp came up for $300, from an honest-appearing seller and I bought it.
Last night I opened the box, pulled it out, found the amp covered with styrofoam bits, and opened it up to vacuum it out, and to look for leaky caps.
I cleaned the styrofoam and the dust out of it, and unscrewed the input board and pulled the two plugs for Q201 and Q301, the 2SA1376 and 2SC3478 "temperature-compensated DC-bias voltage transistors to the input of the triple-Darlingon-follower output stage" that sit on the output transistor boards, to get a little more room to move the input board so I could get a better look at the electrolytics.
The caps and the board looked great, so I put it back together and tested the DC offset. It hunted around a bit, while the unit made a low AC transformer hum, then the hum stopped and the offset settled at 2mV.
That was when I noticed that I hadn't reconnected those two plugs.
Now, of course, the amp is dead.
I get the 2mV offset, and the 10 / 100 / 110 Ω readings between the grounds of the input, output, and power cord previously discussed, but no sound whatsoever.
Since I ran it with the bias transistors disconnected from the input board, it is my hope that I just trashed something on the input board, and didn't trash the power supply or any of the output boards. I've got the parts to completely replace almost all input board components in little plastic baggies, and I've got a (probably) good input board on my other amp, so any of those would be a fairly easy fix.
Does anyone have any thoughts on this (other than that I'm not that bright)?
If I don't hear anything, then I'll probably try swapping the input boards tomorrow, but I have to admit, I'm not in a very good mood tonight.
Thanks in advance,
- Eric
Greetings, all.
I am back, having done something really stupid, and wondering whether there might be a simple answer.
To pick up the story:
In April of 2009, I tested the amp as instructed, then ran into a dead end, and, not being trained in electronic troubleshooting, could go no further.
The system was working on two amps, and I got a new job that took some of my attention away from this problem, and, honestly, I was disgusted.
I watched eBay for replacement amps, and noticed the prices go up more or less as soon as I decided to buy one. There was no way I was going to spring for $500 for an amp, so I kept watching and waiting. It became a habit.
Finally a few weeks ago, and amp came up for $300, from an honest-appearing seller and I bought it.
Last night I opened the box, pulled it out, found the amp covered with styrofoam bits, and opened it up to vacuum it out, and to look for leaky caps.
I cleaned the styrofoam and the dust out of it, and unscrewed the input board and pulled the two plugs for Q201 and Q301, the 2SA1376 and 2SC3478 "temperature-compensated DC-bias voltage transistors to the input of the triple-Darlingon-follower output stage" that sit on the output transistor boards, to get a little more room to move the input board so I could get a better look at the electrolytics.
The caps and the board looked great, so I put it back together and tested the DC offset. It hunted around a bit, while the unit made a low AC transformer hum, then the hum stopped and the offset settled at 2mV.
That was when I noticed that I hadn't reconnected those two plugs.
Now, of course, the amp is dead.
I get the 2mV offset, and the 10 / 100 / 110 Ω readings between the grounds of the input, output, and power cord previously discussed, but no sound whatsoever.
Since I ran it with the bias transistors disconnected from the input board, it is my hope that I just trashed something on the input board, and didn't trash the power supply or any of the output boards. I've got the parts to completely replace almost all input board components in little plastic baggies, and I've got a (probably) good input board on my other amp, so any of those would be a fairly easy fix.
Does anyone have any thoughts on this (other than that I'm not that bright)?
If I don't hear anything, then I'll probably try swapping the input boards tomorrow, but I have to admit, I'm not in a very good mood tonight.
Thanks in advance,
- Eric
Well, THAT was easy...
So I was all ready to start swapping parts after doing something stupid, when I had a thought: What about those fuses?
I'd looked at all three fuses - they were all the type with the paper liner that burns if the fuse blows, and they all looked perfect - but I hadn't tested them.
So, first thing, checked the fuses, and sure enough, one of the runners was blown. Replaced it, closed up and reconnected (looking VERY carefully to be sure I didn't forget to connect anything), and YES, it worked!
Nice to know that even though I do stupid things, they're not always fatal.
I was having such a nice time listening to my stereo in its proper tune again that I nudged the gain of the 1812 Overture up a bit more than I'd done before, and OUCH! that cannon made a bad sound.
Blew a woofer on a QLS-1. Crap.
Anyone know a good speaker shop?
- Eric
So I was all ready to start swapping parts after doing something stupid, when I had a thought: What about those fuses?
I'd looked at all three fuses - they were all the type with the paper liner that burns if the fuse blows, and they all looked perfect - but I hadn't tested them.
So, first thing, checked the fuses, and sure enough, one of the runners was blown. Replaced it, closed up and reconnected (looking VERY carefully to be sure I didn't forget to connect anything), and YES, it worked!
Nice to know that even though I do stupid things, they're not always fatal.
I was having such a nice time listening to my stereo in its proper tune again that I nudged the gain of the 1812 Overture up a bit more than I'd done before, and OUCH! that cannon made a bad sound.
Blew a woofer on a QLS-1. Crap.
Anyone know a good speaker shop?
- Eric
Sorry to revive this thread again. I recently got a pair of the 565's and going about restoring them. I started with the worse one as well, with instant distortion light on. I've scrubbed the boards top and bottom like crazy with simple green and a paint brush. This got the one amp working great, right up until I started turning up the volume. It was pretty loud and the sound just suddenly changed to very muddy and distorted, but still loud. I was using a NAD receiver as the preamp since it has jumpers. Now I'm not sure what I could have blown, whether it was the outputs or inputs or something else. I'm wondering if anyone is familiar with this symptom. I'm leaning towards Q111 and Q112 going bad, but it could also be the Servo IC or really anything for that matter. After this happened I took it apart and scrubbed it yet again with simple green very thoroughly. It powers on fine, no instantaneous distortion and offset looks fine. But the sound is just muddy and distorted coming out, but it still can go loud I think ( I didn't want to push it at this point). Could anyone point me in the right direction?
Hello everyone!
I just logged into diyAudio after a few years and wanted to revisit this thread and report on my 565s.
It has been nearly 8 years since you all (primarily anatech) and I rebuilt my pair of GFA-565 monoblocs and they are still running strong and still sound absolutely amazing today.
The enjoyment from listening to my hi-fi system running these monoblocs is priceless. What makes it especially great is knowing how the amps function, what's in them, and how much effort we all put into rebuilding them.
I just wanted to say thanks again.
BTW: my business of repairing amps is now long defunct as it was never a good idea to work on other people's equipment without having a solid technical background. Anatech was very right.
My next project is to find, buy and repair an ADCOM GFA-585 Limited Edition stereo amp, to be used in a new stereo system I'm assembling with bookshelf speakers and powered sub running a passive preamp direct to a digital audio PC with a high-end sound card and on-board DAC. I'm planning on giving the 585 an "MJR" workover like how I did my 565s. I'm greatly looking forward to that project!
I just logged into diyAudio after a few years and wanted to revisit this thread and report on my 565s.
It has been nearly 8 years since you all (primarily anatech) and I rebuilt my pair of GFA-565 monoblocs and they are still running strong and still sound absolutely amazing today.
The enjoyment from listening to my hi-fi system running these monoblocs is priceless. What makes it especially great is knowing how the amps function, what's in them, and how much effort we all put into rebuilding them.
I just wanted to say thanks again.
BTW: my business of repairing amps is now long defunct as it was never a good idea to work on other people's equipment without having a solid technical background. Anatech was very right.
My next project is to find, buy and repair an ADCOM GFA-585 Limited Edition stereo amp, to be used in a new stereo system I'm assembling with bookshelf speakers and powered sub running a passive preamp direct to a digital audio PC with a high-end sound card and on-board DAC. I'm planning on giving the 585 an "MJR" workover like how I did my 565s. I'm greatly looking forward to that project!
Last edited:
Got a pair of these tooo!!
Hi Guys;
I've read every thread about the GFA-565, and learned a lot about the proper way to maintain (or fix) the amps properly. I also bought a nice pair of GFA-565 amps, recently, and will have to work on one of the two. The previous owner had the caps replaced on both amps, however, he told me that they did not leak on on of the amps. One amp (the one where the caps did leak)has an issue where the woofer is sucked in for about half a second , when theiamp is being turned off.
I received the amps on monday, and I will soon remove the main boards, and clean them with an ultrasonic cleaner, just to make sure no acidic residue remains on the boards. I will also replace all the caps again (for this, i bought new panasonic FC caps all rated 105c from Digikey). Also bought a couple of OP97 op amps, and will probably replace the one on the problem amp.
I found that this thread is very interesting and informative. The GFA-565 is a very well built amp, and I dont plan on replacing any components that are not defective (other than the caps). My GFA-565 seem to be an early production units, serial 28 and 58. I've noticed that they dont have the electrolytic caps on the power output heat sinks, like i have seen posted on other pictures here. The power output board dont seem to have a place for them, either. I've noticed them of the schematics, though, (labeled as note: 4). I've also ordered a few 10ohms 1/4w 5% fusible resistors, in case some of them are defect. Wasn't able to locate any of the 82ohms 1/4w 5% fusible, anywhere, You need to buy a 5000 package to get them....
I will keep the community informed of my progress. Yves.
Hi Guys;
I've read every thread about the GFA-565, and learned a lot about the proper way to maintain (or fix) the amps properly. I also bought a nice pair of GFA-565 amps, recently, and will have to work on one of the two. The previous owner had the caps replaced on both amps, however, he told me that they did not leak on on of the amps. One amp (the one where the caps did leak)has an issue where the woofer is sucked in for about half a second , when theiamp is being turned off.
I received the amps on monday, and I will soon remove the main boards, and clean them with an ultrasonic cleaner, just to make sure no acidic residue remains on the boards. I will also replace all the caps again (for this, i bought new panasonic FC caps all rated 105c from Digikey). Also bought a couple of OP97 op amps, and will probably replace the one on the problem amp.
I found that this thread is very interesting and informative. The GFA-565 is a very well built amp, and I dont plan on replacing any components that are not defective (other than the caps). My GFA-565 seem to be an early production units, serial 28 and 58. I've noticed that they dont have the electrolytic caps on the power output heat sinks, like i have seen posted on other pictures here. The power output board dont seem to have a place for them, either. I've noticed them of the schematics, though, (labeled as note: 4). I've also ordered a few 10ohms 1/4w 5% fusible resistors, in case some of them are defect. Wasn't able to locate any of the 82ohms 1/4w 5% fusible, anywhere, You need to buy a 5000 package to get them....
I will keep the community informed of my progress. Yves.
So, i tested the amps yesterday. The first a is almost perfect. Bias jumps to about 200 mv on powering up, but returns to 10 - 12 mv after about 5 minutes. Will need a little adjusting. However, the second one, has the symptoms of a bad cleaning job after the caps were replaced. Bias jumped to 2.4v, on powering up, but stayed at 2.4v, throughout the test. But when i turn the amp off, bias jumps to 19v, and settles at 14v, until the supply caps are empty. So i guess i'll have a bit of work to do on that amp to bring it back to shape. First step, a good ultrasonic bath and cleaning will be beneficial, i'm sure.
I have a question for you Mika: Can you tell me the exact part # of the Weco screw terminal that you used on your GFA-565 amps, and where did you get these? I tried to find something similar, but was unable to find anything. Will also be looking for the small gold plated pins. I think its a good idea.
I have another question: Do the GFA-565 amps all have a ground pin on the 120v AC plug? My amps dont have any ground pins on the AC plug. 😕
So i guess i'll have a bit of work to do on that amp to bring it back to shape. First step, a good ultrasonic bath and cleaning will be beneficial, i'm sure.I have a question for you Mika: Can you tell me the exact part # of the Weco screw terminal that you used on your GFA-565 amps, and where did you get these? I tried to find something similar, but was unable to find anything. Will also be looking for the small gold plated pins. I think its a good idea.
I have another question: Do the GFA-565 amps all have a ground pin on the 120v AC plug? My amps dont have any ground pins on the AC plug. 😕
Hi mjraudio,
Thanks ...
Why would you use a balanced input circuit? Do you currently have noise problems?
You can buy chips that convert a proper balanced input into a single ended one. But understand that you are adding another circuit on top of what is there already. Personally, I wouldn't go balanced unless there where noise problems that couldn't be solved any other way, or if you were going to send a signal a longish distance.
Hi ypelchat,
Your misbehaving amplifier is showing classic signs of electrolyte leakage, or TIM. TIM= Technician Induced Malfunction. It is entirely possible that it is breaking into oscillation as well. You should have access to an oscilloscope to check a few things.
The electrolyte is colorless, but you can smell it the second a soldering iron tip touches it. It stinks. I was working on an HP 3336B audio generator yesterday and guess what I smelled? Yes, some dummy used cheap capacitors to "recap" this piece of equipment. It's a good thing I was replacing the capacitors anyway as many test bad now. The equipment was born in 1979 I think. Now it's time to replace some front panels connectors over to BNC.
-Chris
Thanks ...
Why would you use a balanced input circuit? Do you currently have noise problems?
You can buy chips that convert a proper balanced input into a single ended one. But understand that you are adding another circuit on top of what is there already. Personally, I wouldn't go balanced unless there where noise problems that couldn't be solved any other way, or if you were going to send a signal a longish distance.
Hi ypelchat,
Your misbehaving amplifier is showing classic signs of electrolyte leakage, or TIM. TIM= Technician Induced Malfunction. It is entirely possible that it is breaking into oscillation as well. You should have access to an oscilloscope to check a few things.
The electrolyte is colorless, but you can smell it the second a soldering iron tip touches it. It stinks. I was working on an HP 3336B audio generator yesterday and guess what I smelled? Yes, some dummy used cheap capacitors to "recap" this piece of equipment. It's a good thing I was replacing the capacitors anyway as many test bad now. The equipment was born in 1979 I think. Now it's time to replace some front panels connectors over to BNC.
You know what? I haven't noticed this, but I think they were all just a polarized plug here in North America. Adding a chassis ground may induce hum. Don't change anything in that regard.
-Chris
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.