Fixed my GFA-585

ben62670

Well after battling my problems with this amp for a year now I am finally in the home stretch with this brain teaser. These are known to be hard to work on, and very dangerous, but I'm not too bright so... I decided to take it on myself(with some diyaudio forum help:)thanks H9).

The Old Adcom's (585's, and 565's)suffer from a bad run of Elna capacitors that leak electrolyte onto the circuit boards which causes noise, and DC offset. If used in this state you can damage your speakers, or your amp. To fix these you have to remove all the caps on the input board, and clean them with simple green mixed with water 10/1. Well I cleaned these suckers 3 times, and still had the DC offset problem. I just ran it anyways. With the number of drivers it was hooked up to I wasn't worried about damaging the speakers.

Well doing some experiments with different crossovers in my custom SDA's I accidentally shorted one of the channels. POOF! I blew a transistor in both channels. No big deal right. Wrong. You need to replace the whole set with beta matched transistors. OK now I need to purchase about 40 transistors to get 20 that would be close enough to use. I wanted to get the job done right. The Toshiba transistors that are used in the older Adcom's are no longer available. That bummed me out. I love the sound of the big GFA's. So I went on a hunt. Finally about 9 months later I found this guy on Ebay selling the transfo's I needed. The problem was he was selling 500:eek:

So I won 500 transistors. I could not for the life of me figure out how to beta match them. So I bought an old Heathkit 121 transistor tester for $60 on the bay. Now I have all the transfo's I need:D, and a tester. So I rebuild the outputs, and test it. No big surprise. 1vdc of dc offset:( THE ONLY WAY TO REMOVE THIS NASTY DIELECTRIC IS TO USE AN ULTRASONIC CLEANER!.

So now I have an ultra sonic cleaner:D I took the input boards back off the amp, and tested every resistor, and diode on that sucker. I also replaced the OP-Amp that sets the DC offset servo. For haha's I replaced a few of he voltage regulating transistors too. I found some bad diodes that were leaking back wards, and replaced them. Put everything back together, and fired her up.

It took a little while for her to settle down. Had some DC offset. I had to set the bias to 24mv a few times. After about 5 hours of breaking the "new amp in" she self corrected the DC offset to specs well within the acceptable range. I have DC offset from 0(yeah you read that right:cool:) to 10mv:D Well it's almost completely done! I have just a couple of caps that I am going to replace (105c) instead of the 80c caps I have in there now, and I am ready to button her up. I might install some beefier main caps, and I am definitely going to add some active cooling via 120cm 12v fans. I don't need much just some slow quiet fans. These Adcom's could literally cook an egg.

Thanks for reading. My shrink suggested I right right down trials that I have had in my life, and read them. Plus I just wanted to share my experience with you guys. your the best:)

Ben

ben62670

Well I finished that one yesterday. Late last night I was working on a home built amp. I have a GFA-555 transfo. Not sure what I want to do with this one yet. I might be stacking transformers though. I can not find a big enough one to do what I want to do.

rskarvan

Sounds like you are seriously committed to saving that Adcom amp. Great job!!!

jakelm

Geezzz Ben, you could right an electronic novel on the projects you take on.

Let me ask, if I may. You might know this.

My old Hafler is starting to get a bad humm from the amp itself. I have already replaced the PS caps. What causes this humm? At night when everything is quiet, I'm sitting 13' from the amp and the amp in in a bookshelf, with no back but with a vented door. And I can still hear this hum, sometimes its louder than other times.. Is it the power supply that s going bad?

ben62670

Jake.
I doubt the PS is going bad. A lot of the time there is a small cap crossing the main caps terminals. Find out what the value of that cap is, and replace it. If that doesn't work try DIYaudio. I have been spending a lot of time over there. Those guys are great. You have gone through the normal hum hunting routine correct? Cheater pugs, disconnect cable/Sat TV, no dimmer switches involved, AC, or heat not turning on. Some of the old Adcom's have a faint 60hz buzz just from the transformer. It is very subtle at most times. You have to be right there to hear it. I would also recommend taking a MM, and reading the DC voltage across the pos/neg terminals. Set it at like 2vdc at first, and then set it at mv, and see what you get for a reading.

jakelm

ben62670 wrote: »

Jake.
I doubt the PS is going bad. A lot of the time there is a small cap crossing the main caps terminals. Find out what the value of that cap is, and replace it. If that doesn't work try DIYaudio. I have been spending a lot of time over there. Those guys are great. You have gone through the normal hum hunting routine correct? Cheater pugs, disconnect cable/Sat TV, no dimmer switches involved, AC, or heat not turning on. Some of the old Adcom's have a faint 60hz buzz just from the transformer. It is very subtle at most times. You have to be right there to hear it. I would also recommend taking a MM, and reading the DC voltage across the pos/neg terminals. Set it at like 2vdc at first, and then set it at mv, and see what you get for a reading.

There is no cap across (between) the PS caps, just a solid wire with both -tive terminals soldered to it. I have disconnected all inputs and speakers, humm remains. I can also feel the hum when I put my hand on the amp.

There is no hum or noise form the speakers, this hum is localized in the amp itself. I

It sounds like a 60hz hum from transformer, cause when I turn it on, there is a louder hum then it quiets down.

It freaked me out the other night, I was walking around the living room trying to find where the hum was coming from. I thought it was coming from the HK, then the DVD player, but found it at the Hafler.

I will test the Dc voltage tonight and let you know what it reads. To test, I disconnect all inputs and speakers right?

No cheater plug, because the original power cord is only a 2 prong plug.

ben62670

Yep. Everything disconnected.

jakelm

Did I read correctly? Stacking transformers? Is that going to create a heat issue?

heiney9

jakelm wrote: »

Did I read correctly? Stacking transformers? Is that going to create a heat issue?

A lot of dual mono designs use stacking transformers. They must deal with the heat a certain way.

WilliamM2

Good to hear you got the 585 working. But did I read it correctly? Did you just clean the Elna caps, or did you replace them?

ben62670

WilliamM2 wrote: »

Good to hear you got the 585 working. But did I read it correctly? Did you just clean the Elna caps, or did you replace them?

No sir. I replaced all the electrolytic caps except for the filter caps;)
I have some 105c caps coming in Wed, and then I can button this thing up, and call it done. Just as an FYI for anyone reading this all electrolytic caps, and variable resistors (pots) must be removed prior to any liquid cleaning. For now I need to hook up both amps. The 5800 on the dims with the grounds tied, and the 585 on the stereo. I don't need that much power, but I am running at 2.6ohms right now. Not the best for longevity.

heiney9

Nice work Ben glad Chris over at DIYAUDIO could help you through it. I hope my brother's 585 never has it's caps leak. I'm sending it to you if it does. ;)

ben62670

heiney9 wrote: »

A lot of dual mono designs use stacking transformers. They must deal with the heat a certain way.

If transformers are getting hot there is a big design problem. I may just build a 3 tier amp chassis with transformers in the bottom, caps in the middle, and input stages on the top tier. The outputs would run up the back. I'm thinking size wise about the size of an apartment fridge. About 24x24x36 water cooled. I have been working on a selectable SS/tube active XO/Pre amp for a while now. I have not liked the 24db XO designs so far, but I can get the 12db to sound real nice. I may install a marine deep cycle battery under the hood for the low voltage stages. You can not get any cleaner than battery power, and who cares about a battery in a box that big. I may have to vent it separately so the risk of battery explosion is nilled. The cool thing is it will be like a tube/Integrated amp, or a standard amp with a flip of the switch. For the highs at least, and I may do this on the mids too. I will be able to raise the hood on this project very easily;)

ben62670

heiney9 wrote: »

Nice work Ben glad Chris over at DIYAUDIO could help you through it. I hope my brother's 585 never has it's caps leak. I'm sending it to you if it does. ;)

Please replace the caps before they leak. It is a 2 hour job max. If they say Elna on them they will leak. It is an easy job to do before the problem arises. If they leak it is a nightmare. I am talking a lot of hours here, and finding the components that nasty stuff took out in its travels. I had to go over every resistor, and diode in the input stages. Also Chris told me which transistors can be effected by the leaky caps. I just replaced them as a precaution. Please have him change the caps before they go bad. Its less than $10 in parts. When I get to GA, and you want me to replace them there I would be more than happy to help out. I could have never come this far if you didn't point me in the right direction;)

vonnie123

Ben are those type (brand) of caps limited to the GFA 565s and 585s, or are they present in the other Adcom amps of that era? e.g., 555s, 545s. Will be interesting to see if there is any variation in how you feel the amp sounds after the repairs.

ben62670

The repair is done. There is validity to different caps in the signal line. These caps that are in question are just PS caps that are just reserves for input board power. I imagine they are in some of the other amps too, but the majority of the amps in question were the 565, and 585 amps.

heiney9

vonnie123 wrote: »

Ben are those type (brand) of caps limited to the GFA 565s and 585s, or are they present in the other Adcom amps of that era? e.g., 555s, 545s. Will be interesting to see if there is any variation in how you feel the amp sounds after the repairs.

Those were the only 2 amps affected and even then it's not all of them.

engtaz

Congrats on getting the amp done.

engtaz

ben62670

Thanks Roy. I am still waiting on getting a couple tubes for that other project you sent me:)

SKsolutions

You know it's love when you go through all that, and at that point, you can really call it a hobby and a passion. It's a distinction that's seldom made so clearly. Congrats on the resurrection of a such cool piece.

ben62670

Killed it today. I was messing around with my speakers, and had a temporary XO mod on the tweeters. It was a cap,and resistor in parallel to try to give the top end a little boost. Well that was working fairly well, and the new 15" sub in the mains was working fairly well. Good enough to vibrate the binding post loose enough so the cables shorted blowing out the left channel. So I pulled out the output transistors and beta tested all of them. They were fine. I then tested all the resistors and found that each channel had 10 10r 1/4w fusible resistors. I had some 1/8w 10r carbon films so I installed them. Sounds better than before. I am not a fan of fusible resistors. I am going to order up all the resistors to redo my 585, and my 565's, and new caps. Also I should have a 545 on the way:)
Ben

Ender

LOL. You can be that uncle that tells funny and adventurous stories. Gonna call you Uncle Ben from now on.

nooshinjohn

ben62670 wrote: »

Killed it today. I was messing around with my speakers, and had a temporary XO mod on the tweeters. It was a cap,and resistor in parallel to try to give the top end a little boost. Well that was working fairly well, and the new 15" sub in the mains was working fairly well. Good enough to vibrate the binding post loose enough so the cables shorted blowing out the left channel. So I pulled out the output transistors and beta tested all of them. They were fine. I then tested all the resistors and found that each channel had 10 10r 1/4w fusible resistors. I had some 1/8w 10r carbon films so I installed them. Sounds better than before. I am not a fan of fusible resistors. I am going to order up all the resistors to redo my 585, and my 565's, and new caps. Also I should have a 545 on the way:)
Ben

am glad to see you so determined to save the Adcom... they were/are pretty good amps. Have you thought about doing this kind of stuff as a business? You seem to have a bit of a gift there
... and have you thought about getting a sunf$@*.... better not go there:o

Face

That's why I like to use my Mac while testing, you can touch the leads together all day and not have to worry.

heiney9

Face wrote: »

That's why I like to use my Mac while testing, you can touch the leads together all day and not have to worry.

Yeah, the Aleph doesn't stress out over shorted leads, do it all day long. Sorry to hear Ben that is a real PITA

ben62670

With this speaker I wanted to be able to swap out the components for the RC easily, and being finished I could tack the parts down. Oh well this little mishap just solidified I need to get on those amps. I know you know the difference resistors can make. Not a lot of caps in there. Time to build an excel spread sheet and get some resistors ,caps, and toss a few OpAmps in there for some other projects. All I need now is some money.

ben62670

Face wrote: »

That's why I like to use my Mac while testing, you can touch the leads together all day and not have to worry.

heiney9 wrote: »

Yeah, the Aleph doesn't stress out over shorted leads, do it all day long. Sorry to hear Ben that is a real PITA

No problem it is already fixed, and running:) I can do these 565's and 585's in my sleep;)

Michael_Js

great!! ...

ben62670

Dibs