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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 28 Dec 2014, 00:25 
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Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
Ok, as I recall, the service manual on indicates value and voltage rating. You would need qty. 4 pieces of 6800 uF 63V caps. I'll pull out the board I still have and measure diameter and lead spacing. I do recall in measuring the original caps, the actual reading was on the plus side, around 8000 uF.

I'll get back to you on physical measurements of the caps.

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Rega P25 and LFD Mistral phono (analog) or Oppo DVD Player (digital) > Aunt Corey's Buffered Pre > Adcom GFA 535 > Spica TC-50


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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 30 Dec 2014, 23:10 
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Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
I can't find the board but the service manual has a layout of the psu pcb. It looks like the lead spacing is 15 mm and the cap has about a 30mm diameter.

I took a quick look in the Mouser catalog and they actually do have 6800uF 63V caps in stock, but the lead spacing is 12.5 mm, not 15. For myself, I might be tempted to drill a pair of holes 12.5mm apart, scrape off some of the protective silk screen, and solder them so that I could glue them flush to the board and not have excess leads/bent leads. But that's just my crazy opinion.

One part is Nichicon UVY1J682MRD. But the only thing I can say to the negative is that 6800uF is just not enough as I found out by upping to 10,000 uF snap in type caps.

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Rega P25 and LFD Mistral phono (analog) or Oppo DVD Player (digital) > Aunt Corey's Buffered Pre > Adcom GFA 535 > Spica TC-50


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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 19 Jan 2015, 22:29 
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Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
I just noticed it's been 5+ years since I started work on the Adcom GFA-535 and the music is still playing. Sweet.

In that time I've learned quite a bit and I suddenly got the itch to redesign the psu board from scratch. Why? Well, I've learned a few tricks and seems you can drop the measured inductance of the board with a dual layer version. I'm faster now at board layout so this is coming together more quickly..or maybe I played with the psu layout for 5 years that it should be easy by now. Ha.

Some of you guys asked for more tips and by dumb luck at the time, I did something right. You'll see many diy projects out there where the power supply wires and audio carrying wires are twisted together. If you look at the left channel board, you can see where I have a triple braid of wire. That's B+, Ground, and B-. B was used by Adcom so I'll stick to that for now. You should definitely do that. It will help cancel out the EMI generated. Trust me, just do a triple braid for each channel. In my case, the right channel is missing the ground wire...it was made that way. I have no clue why but it goes against what is printed in the schematic. So I'll be opening up the Adcom and fixing that.

I also realized a few weeks ago (DUH!) that the service manual not only lists the transistor part number, but the acceptable beta grade. If your savvy and can't find the original parts out there, then at least you can find a sub with the acceptable beta specs for the amp. I'll post that info very soon.

Also, I promised key resistors to replace in your Adcom so I'll post that soon. We all know that capacitors can give out, but you can get good bang for the buck by replacing certain resistors.

Chat with ya'll soon and I hope anyone who cracked open their amp was able to rebuild it successfully! Happy music! :sing: :headphones:

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Rega P25 and LFD Mistral phono (analog) or Oppo DVD Player (digital) > Aunt Corey's Buffered Pre > Adcom GFA 535 > Spica TC-50


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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 10 May 2015, 14:34 
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Joined: 10 May 2015, 11:58
Posts: 3
Hi guys:

Just picked-up a GFA-535 amplifier for $25.00 on eBay, :D that i bought as a rebuild project. It's got a defective right channel, and I'd like to find a service manual for it. This thread is very interesting. Thanks.


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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 15 May 2015, 21:19 
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Joined: 10 May 2015, 11:58
Posts: 3
Looks like i won't need a service manual, after all. ;o). Got the amp in the mail today. So I popped the cover open, only to find that the B+ 4A fuse of the right channel, was blown. I replaced it,and the right channel came back to life again. Not bad for a $25.00 GFA-535. ;o))))))


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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 29 Jun 2015, 00:45 
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Joined: 02 May 2015, 01:06
Posts: 1
Has anyone found direct replacement drop-in caps yet. Need to recap, but not sure what to get...


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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 27 Jul 2015, 11:52 
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Joined: 10 May 2015, 11:58
Posts: 3
Bought another one on ebay ($30.00), with a defective channel. That one gave me a little more trouble getting it to work, but i manage to rejuvenate that one as well.

The amp came in with the defective channel fuses, removed, so i though i might have to replace many parts to bring it back to life. I put in new fuses, and decided to risk applying ac main, just to see if... Nothing happened. but no sound. Then I touched the input post with my finger, to see if i would get hum on the output. Nothing. No sound at all. Using the service manual, i then checked All the voltages on the circuit. All were correct.... So i was puzzled. I decided to let it run for some time. Both heat sinks had about the same amount of heat. So i thought that the amp looked like it's operating normally, and the output transistors seemed to be ok. So, i unplugged it, to let the condensers discharge. I've unscrewed the channel heat sink from the amp's casing. I took a soldering pencil, and proceeded to re-wet every solder joints on that channel's circuit board. I noticed one solder, that looked correct, but seen through the magnifying glass, it looked like a cold solder joint. Anyway, i decided to re-wet all solder on that particular channel. I had nothing to loose. After that, i re installed the channel back in place, I applied AC main. BINGO! The channel is now operating perfectly. So if you have a problem with a GFA-535, the first step i suggest, is to review all solder joints. I was not impressed by the quality of the soldering on these amps. Looked like they were soldered by hand.:D


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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 30 Apr 2020, 21:57 
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Joined: 29 Apr 2020, 23:15
Posts: 1
Hi, I very much realize that this thread is really old, but I stumbled across it after buying a GFA-535 and looking for upgrades. I have to say I'm really impressed and I learned quite a lot. So, 5 years later, thank you. I was also looking to see if the rev_3 pcb and bom were the latest here. I also wanted to know if you're affiliated with this guy: https://hoppesbrain.com/product/adcom-g ... upply-kit/

Looks like he has done a lot of the same things you have... like... way too similar...

I don't even know if you're around on this forum anymore, I'm new here and I don't think I can even look at user profiles.

Anyways, I hope it's okay that I posted in here... Thanks in advance.


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