Adcom 585 incoming

littlewoodboats

After asking and reading here I had decided on an Adcom 555 to have rebuilt. With the different models of the 555 I had no clue which one to look for so I called a man named Rick at Big Sky Audio for advice. Big Sky is listed on the Adcom page as a repair center and the only place that would discuss anything more than replacing the out of spec parts. The place in Austin told me they only replaced caps if visually leaking and did not do total replacement in one shot.

As fate would have it someone had contacted them about selling a 585 in need of refreshing due to leaking caps. Big Sky put me in contact with the owner out in CA. We came to an agreement with the amp due to hit the shop tomorrow. Estimated turn around is two weeks.

While the amp is in for service are there any upgrades over the basics that should be considered? I will be swapping the power for a detachable cord. They seem to have a stock of Blackgate caps. I have read good things about the Blackgates but wonder if they are worth the extra money. I have also seen where longevity might also be in question.

The 585 has enough power to blast my 2a's into orbit so increasing power is not a concern.

Having spent my working life in and around industrial shipyards I doubt I could hear subtle differences anyway.

Any thoughts?

lanchile

That is a nice amplifier! what I would do is:

-Check for out-of-tolerance resistors and replace them.
-Check and adjust bias/dc offset.
-Change all electrolytic caps (Panasonic FC are very good).
-Replace those big can caps for many smaller values like 6800uf X 8 (lower ESR).

littlewoodboats

I am not sure what you refer to when you say ESR.

All the resistors and small caps are on the list. Everything else is checked and adjusted to bring it all back into spec.

Here are a couple of images.

littlewoodboats

Here are a few more images.

heiney9

IIRC, the 585 is a non-common ground amp so unless the negative terminals can be strapped then you can't use it with those SDA's. Early SDA's like your 2A's can't use the AI-1.

That said, a refreshed 585 is a very nice amp. IMO, at this point the cost of Black Gates isn't worth it. Panasonic FC's are a very good choice (for the power supply) and hella cheaper. Nichicon Muse or Nichicon FG or Elna Silmic for signal path electrolytics are very nice.

H9

P.s. if you search the archives, IIRC the negative terminals can be strapped to create a common ground. But please check with someone before doing it. Maybe FTGV will chime in and confirm.

heiney9

littlewoodboats wrote: »

The 585 has enough power to blast my 2a's into orbit so increasing power is not a concern.

My 30wpc Aleph can launch my 1C's into orbit, so it's not always about increasing the raw power.

H9

heiney9

Hopefully the damage from the leaking caps hasn't damaged the PCB's. The only soultion is to strip them and clean them. Replacement PCB's haven't been available for quite a few years. If the electrolytic gunk sits on there too long it will ruin the traces. Do you know how long the caps have been leaking or how long it's been sitting in that condition?

Good luck.

H9

littlewoodboats

This unit has been sitting in a closet for the past five years. Rick at Big Sky reviewed the images and felt things were going to be fine. His comment was that he has seen and resurrected units that appeared much worse. I can only hope once it is in his hands.

The 585 will need to have the grounds tied together. Definitely something to stay on top of to be absolutely certain. First do no harm

I understand what you are saying regarding power. My little 17 watt stuck in class A could do damage as quick something that would over power. Discretion with the loud knob will be required. Reading many of the upgrade threads the first comment is something related to boosting the output. I do not see that as an issue in this case.

Thanks for your replies.

heiney9

Big Sky seems to be well regarded so I'm sure they will do a fine job. I did do some searching and you will need to tie the negative grounds together to make the 585 common ground, but be sure and ask Rick at Big Sky about it to be 1000% sure.

H9

pitdogg2

heiney9 wrote: »

Big Sky seems to be well regarded so I'm sure they will do a fine job. I did do some searching and you will need to tie the negative grounds together to make the 585 common ground, but be sure and ask Rick at Big Sky about it to be 1000% sure.

H9

How about just asking Rick while he's in it and has it tore down if there is a way he could make it common ground so you do not have to strap together the negative's.....

heiney9

pitdogg2 wrote: »

How about just asking Rick while he's in it and has it tore down if there is a way he could make it common ground so you do not have to strap together the negative's.....

Only downside if the the OP gets rid of the SDA's or wants to use another speaker with the 585 at some point in the future.

H9

littlewoodboats

I was wondering about having the tied together internally to just be done with it and to protect against any forgetfulness I might experience in the future.

Why would the amp being common ground be a problem for a future speaker choice? An internal solution with a toggle switch on the back and it could be either.

Anything can happen in the future but at this point were I to switch speakers it would be for a set of 2B's so I could do the TL conversion. I like the sound of the 2A's and would take a loss selling them so for now they are here to stay.

heiney9

The AI-1 is a better sounding solution than tieing grounds together. If in the future you own SDA's that can use the AI-1 that's a better solution than tieing grounds. Nothing to forget, you buy a couple heavy duty spade terminations for each end of large cable and put them under the speaker nut.

Clean, simple, cheap and completely reverseable.

There is a reason certain designs are not common ground so I would un-do the strap if I wasn't using SDA's to return the amp to it's intended use, but that's just me.

H9

unc2701

It wouldn't be a problem for future speakers, but you'd lose some channel separation. A toggle switch would be super easy to implement: one position and the negatives are connected, the other position is just open.

I'm looking at the schematic, and I'm pretty sure the negatives are at ground potential, but the scan is pretty crappy and split across pages, so have your tech confirm.

littlewoodboats

I am all for clean, simple, cheap, and reversible.

I am perfectly comfortable taking and following your advice. Appreciate it.

unc2701

heiney9 wrote: »

There is a reason certain designs are not common ground so I would un-do the strap if I wasn't using SDA's to return the amp to it's intended use, but that's just me.

To clarify: There are some designs that are not common ground and cannot be made so: these tend to be high-power designs where you basically have two amplifier modules per channel run in series. Put differently, it's a pair of stereo amps, each run in brigded-mono mode crammed into one chassis. On these amps, the negative terminal is the inverse of the positive terminal and strapping the two negatives together will fry your amp.

The other "non-common ground" that can be made so are dual-mono designs where the left and right channels are completely isolated, but the negative terminals are both at ground potential. These can be made to work with SDAs by strapping the ground together.

I believe that the 585 is the latter type.

drumminman

I think H9's solution of strapping the negatives together with a short piece of speaker cable is safer. If you have a toggle switch installed it'd be too easy to inadvertantly flip it to the wrong position.

Then it's a puff of smoke and Ohhhh noooooooooooooooooo! :eek:

unc2701

drumminman wrote: »

I think H9's solution of strapping the negatives together with a short piece of speaker cable is safer. If you have a toggle switch installed it'd be too easy to inadvertantly flip it to the wrong position.

That crossed my mind, too. How about:
http://www.frys.com/product/1926587?source=googleps&gclid=COfwvY_sj7ICFYTd4AodPXEAVg

Hm. Might need to get one of those to replace the power switch on my rig before the kid gets much older.

littlewoodboats

Great knowledge on this board. Tying the grounds together on this amp seems the way to go. I have found reference to it in several areas so should not present any issues. I will check with Rick before proceeding.

Turn around averages three weeks so time to be patient. I hate being patient.

I am expecting great things from Big Sky. They did a full deal upgrade on a members Parasound with what seems to be great result. At the end of the day they were the only ones on the Adcom page of service centers who seemed interested in doing the work.

When it makes it home to Texas I will be sure to post some nudie pics so everyone can see the work. If I had a preamp I would be in good shape. Time to get serious about finding a GFP-750

heiney9

My brother had a 585 and GFP-750 and GCD-750 for awhile. Very formidable set-up. He has since sold all 3 pieces with the GFP-750 going to me.

H9

FTGV

littlewoodboats wrote: »

Tying the grounds together on this amp seems the way to go. I have found reference to it in several areas so should not present any issues.

Yes your good to go.It's a non bridged output stage so each channels negative terminal is connected to ground.However the two channels grounds are isolated from each other with 6.8 ohm resistors so strapping would be required to make those grounds common.
Hopefully the electrolyte has not wandered to far from home since it could potentially cause issues(ie. noise,offset) even if it appears the tech has it all cleaned away.

littlewoodboats

http://bigskyaudiomt.com/index.php?pr=ADCOM_GFA-585_amplifier

Here is a link to the page giving the overview of the service performed. I have never laid eyes on the amp in person as it shipped from CA directly to Montana.

We know there has been some leakage and the images did show some signs of the leaks. Rick seemed to think that it was isolated to only small areas. We are hoping for the best but nothing is known for certain until he gets it on the bench. I have no idea what is involved in Adcoms tech bulletin that covers cleaning. He seems to be able to a good job cleaning and has resurrected a number of these over the years. As long as the residue has not gotten under the traces I am good to go?

I am keeping my fingers crossed.

If you are tired of the GFP-750 I could take it off of your hands. Belonging to you I would imagine it is in excellent condition.

FTGV

Looks like it's in very capable hands.

littlewoodboats

FTGV wrote: »

Looks like it's in very capable hands.

I think your assessment is correct. I threw up a thread asking about Big Sky for opinions of their work and received great feedback.

Thanks for sharing your thoughts.

drumminman

That's an impressive looking amp - looking forward to your impressions after you've spent some time with it.

heiney9

It was designed by Victor Campos and Walt Yung.

Here is an article about the 565 mono's and an interview with Victor. Some of the same ideas and goals were used in the 585. Both the 585 and 565's were to be the pinnacle of Adcom design for the day. Gets into the philosophy of what these two pieces were about.

http://www.stereophile.com/solidpoweramps/adcom_gfa-565_monoblock_power_amplifier/index.html

H9

unc2701

Back to the original question- if you're going to hang on to this and run low-impedance speakers in the future, you might consider having him wire in a fan. This was an option from Adcom when they were selling them and these guys do run hot. With Polk LSI's mine would get hot enough that it was uncomfortable to touch. Not burn-the-house-down hot, but enough to make me nervous. With anything under 8 ohms, they definitely tap out thermally before they run out of power supply. It could be on a switch or heat-activated. Doesn't need to go fast, either: a little air movement goes a long way.

littlewoodboats

Cool link H9. I thought it was a Nelson Pass design. This purchase was a total fluke. I was looking for a 555 to have restored/upgraded. I called Big Sky because I wanted advice from the place where the work would be performed as to which model to search.

While on the phone with Rick he told me someone had e-mailed to see if the shop would be interested in buying this 585. They weren't so he put me in contact with the owner. I talked with the owner on the phone. He had read of the issues and upon opening the case to take photos did notice that some leaking had occurred. He asked me what my plans were if I were to buy the beast and I told him it would go in for full restoration followed by a place of honor in my rack until the day I die. (it will be in my will that it goes into my casket with me prior to burial) As it turned out the amp belonged to his father who had done something different and gave this to his son. The father passed so equipment was not an issue and with life going on around him he was not interested in another project.

We talked about the insane prices on vintage gear and I explained I had a max financial threshold of pain I was willing to endure to own something vintage. I gave him the total I was willing to spend and made an offer based on that. He thought his dad would like it to go to someone who planned to enjoy the amp instead of some flipper looking to make a fast buck. He accepted my offer so the deal was struck (I told him and he knew he could get more listing in on e-Bay). I cannot say enough about how nice the guy in CA was to deal with.

So far I am into this piece for $280.00 including the shipping to Montana. Shipped to Texas I am looking at around $800.00 total

It is not what I was shopping for but I am happy with the transaction thus far. I have done something right in my life for Karma to catch up with me like this. Must be all of the hours I give to the Shrine's Hospitals.


The 565's had a fan option that is supposed to work with the 585 as well. Replaces the top cover I believe. I doubt they are still available but should not be difficult to duplicate should it be necessary. This thing is rated almost double the max recommended for my 2A's so I doubt I stress it to the point of it noticing but something to monitor just in case. Large fan turning slowly. Little noise and as you point out a little air goes a long way. Only time will tell.

heiney9

Cool story and $280 is a steal!! I wouldn't worry about the fan right now. My brother had a 585 and never had close to a heat issue. Wait until it's completely refurbed and everything is back to factory spec and see if heat is an issue. These are not biased that heavily into class A.

H9

littlewoodboats

Speaking of Class A. Is the bias something that can be adjusted? I have no idea what its current spec might be.

I am not seeing the need for a fan at this point. Everything lives on an open rack so airflow has never been an issue.

I read here where you had always spoken well of your brothers amp.

I got an awesome deal and the guy who sold it knows he gave me an awesome deal. He had done his research and knew about the problem and had also seen some of the silly prices. I figured that around $900.00 it was time to consider other options and he agreed with me. That is how the price ended up being what it was.

His father was a total gear head going way back. The seller told me stories of his dad coming in after work talking about the new $900.00 solid gold end interconnects. Dad had collected from the early 60's. He has more stuff that will be coming up for sale. I am not sure if there might be a rule violation but I told him I would post some of his stuff here. I asked for some images so he sent me the ones above plus a dozen more all nice and neat in a Power Point presentation.

His mom will be moving in with him and his wife so all of the extra stuff has to go. There could be some nice deals.

heiney9

Yes, bias can be adjusted but only by someone in the know and you will need to know the factory specs too. Best to leave that to Big Sky.

H9