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PostPosted: Thu Oct 22, 2015 7:26 pm 
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Joined: Fri Jul 04, 2014 8:37 pm
Posts: 340
Location: Toronto, ON, CA
This is an on-going "story" about my adventure with Adcom GFA535. Just got it recently from ebay, and is in progress give it a new life.

People have mixed feelings when it comes to old gears, how long and how well it can perform, is it stable , is there any hidden problems, will the parts be available, and etc... I really wish I could think things through before dived into the marriage, just kidding...but getting old audio equipment need guts, and the spirit of DIY.

Back on the topic, I did study this amp for a while, and I am determined to transform it, that's why I put this thread in DIY section.

To make it more clear, I format following Q&As:
Q: Why GFA535?
A: Some says it was designed by Pass.

Q: Did Pass design GFA535?
A: Strictly speaking, NO. Pass did design 555, Adcom derived two down scaled versions 545, and 535.

Q:What's the difference between 555,545,and 535?
A:Power and chassis dimension mostly. 200W, 100W, and 60W.

Q:Again, why GFA535?
A:It is a well designed amp (Pass blood), it's the cheapest, it has more potential comparing with 545 and 555...

Q:Why 535 has more potential?
A:It has the same PCB as 545...

Progress:
-After got the amp, opened cover, and did a visual check, found a broken fuse, no other noticeable issues...ordered a batch from mouser.
-Replaced all fuses with new ones, power on, running for a while and do some measuring and adjusting.
-Plan for next steps....

-- 23 Oct 2015 03:41 --

Add a back view photo...I hate its binding post.


Attachments:
File comment: It has been taken good care of by previous owner.
00_Inside View.jpg
00_Inside View.jpg [ 190.86 KiB | Viewed 7759 times ]
File comment: Replaced broken fuse, power on, and do some measuring
04_Fuse Replaced.jpg
04_Fuse Replaced.jpg [ 156.64 KiB | Viewed 7759 times ]
File comment: Measured +/- voltage, so it should be 52V after filtered.
05_DC Voltage.jpg
05_DC Voltage.jpg [ 186.05 KiB | Viewed 7759 times ]
File comment: Bias voltage adjusted
07_Bias Adjusted.jpg
07_Bias Adjusted.jpg [ 168.75 KiB | Viewed 7759 times ]
File comment: Heat sink temperature after running 1 hour
08_Sink temperature.jpg
08_Sink temperature.jpg [ 172.98 KiB | Viewed 7759 times ]
File comment: Transformer temperature after running 1 hour or so
09_Transformer temperature.jpg
09_Transformer temperature.jpg [ 142.97 KiB | Viewed 7759 times ]
10_Driving Voltage.jpg
10_Driving Voltage.jpg [ 197.22 KiB | Viewed 7759 times ]
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PostPosted: Thu Oct 22, 2015 7:43 pm 
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Location: Toronto, ON, CA
The binding post requires low gauge speaker bare wires...


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03_Back.jpg
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PostPosted: Fri Oct 23, 2015 1:51 pm 
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Joined: Mon Oct 17, 2011 6:55 pm
Posts: 3010
Location: Toronto, ON, CA
I still own my 535 – 20+ years and still working. Replaced the set of 8 crappy binding posts with just 4 quality ones. And removed the A/B switch from the signal path (kept the buttons but they do nothing). Great little amp that punches well above its price range.


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PostPosted: Fri Oct 23, 2015 2:48 pm 
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Joined: Fri Feb 13, 2009 4:51 am
Posts: 241
Location: kanata, ON, CA
I have two of them. I got the first one to replace a 4B. I thought it would be downgrade. I'm missing the slam of the Bryston but the sound quality is on par. At the time I ran a pair of Stratus Gold and no problem driving a 4 ohm load. Superb amp conservatively rated at 60 WPC.


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PostPosted: Fri Oct 23, 2015 3:50 pm 
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Joined: Thu Jan 27, 2011 5:40 pm
Posts: 946
Location: Waterford, ON, CA
This is a very good amp. My friend has one and he says it's always turned on - it's been running without a burp for 22+ years.

I've owned the 555 and 545, they're all excellent amps, built like tanks and very decent SQ.

I wouldn't be in a big hurry to change anything on it. 8)


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PostPosted: Fri Oct 23, 2015 4:50 pm 
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Location: Toronto, ON, CA
sthomas1049 wrote:
I still own my 535 – 20+ years and still working. Replaced the set of 8 crappy binding posts with just 4 quality ones. And removed the A/B switch from the signal path (kept the buttons but they do nothing). Great little amp that punches well above its price range.


Remove A/B switch is also part of my plan...


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PostPosted: Fri Oct 23, 2015 4:54 pm 
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Joined: Sat Feb 21, 2009 6:48 am
Posts: 159
Location: Winnipeg, MB, CA
Good luck on your start of modding this fine amplifier. I have done 6 of them which I have had over the years. Honestly I only changed a handful of parts which were 4 diodes and 8 capacitors if memory serves correctly. I also tried several resistors but they didn't appear to make any sonic difference. Total of around $30 in parts. You have the Mk I, which I had also swapped the transformers from a Mk II into them as they are 10VA larger.
Good luck, J


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PostPosted: Fri Oct 23, 2015 5:11 pm 
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Posts: 340
Location: Toronto, ON, CA
-Parts on the way...some will need one week or two...
-Collected data from power transformer venders...535 has a very slim body, hard to find a suitable high VA transformer...well, transformer can wait.


What I did tonight:
-Replaced RCA inputs
-Removed amp boards with sinks, gave them a through bath...prepare for recap and other parts replacement


Attachments:
RCA_Before Change.jpg
RCA_Before Change.jpg [ 127.45 KiB | Viewed 7603 times ]
RCA_AfterChange.jpg
RCA_AfterChange.jpg [ 128.69 KiB | Viewed 7603 times ]
File comment: you can still see water on it...
Washed.jpg
Washed.jpg [ 199.26 KiB | Viewed 7603 times ]
Washed2.jpg
Washed2.jpg [ 169.56 KiB | Viewed 7603 times ]
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PostPosted: Fri Oct 23, 2015 5:45 pm 
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Location: Toronto, ON, CA
Sarchi wrote:
This is a very good amp. My friend has one and he says it's always turned on - it's been running without a burp for 22+ years.

I've owned the 555 and 545, they're all excellent amps, built like tanks and very decent SQ.

I wouldn't be in a big hurry to change anything on it. 8)


Thanks for your advice.

The reason why I want make any changes on it, like I said, bring it to its full potential, that should be fun...

-- 24 Oct 2015 01:58 --

Jaxom wrote:
Good luck on your start of modding this fine amplifier. I have done 6 of them which I have had over the years. Honestly I only changed a handful of parts which were 4 diodes and 8 capacitors if memory serves correctly. I also tried several resistors but they didn't appear to make any sonic difference. Total of around $30 in parts. You have the Mk I, which I had also swapped the transformers from a Mk II into them as they are 10VA larger.
Good luck, J


Yes, resistors are not aging the same as elec. caps. If just bring the amp to spec, I will just do recap and probably diodes like you did...

The transformer on my mind will be much bigger...535 comes with 300VA (150VA * 2) I believe, and I am thinking about 600VA. As I am planning to bring its power to 100W per channel, which need transformer 200VA * 300%.
GFA545 claimed 100W*2 output, but transformer is around 400VA, which I consider is not enough.
The problem with 535 is the internal height of the chassis is around 70mm, and most 600VA is taller than that...bummer...but I have talked to Richard from SumR, he can do a 600VA under 70mm, with a bigger OD and lower height core I suppose.

Thanks for the good luck blessing, I really need it ;-) Have a nice weekend!


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PostPosted: Fri Oct 23, 2015 6:20 pm 
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Joined: Sat Feb 21, 2009 6:48 am
Posts: 159
Location: Winnipeg, MB, CA
When I went through all of mine I only had one of the six which actually needed an electrolytic replaced, all of the others measured in spec for capacitance and leakage. The ones I upgraded were all in the signal chain. I found increasing the main power supply caps capacity actually made the amp sound darker, even with 2 smaller bypass capacitors of 47uF and 0.1uF across each.
Good luck fitting larger transformers in the chassis, even if you get one that fits in height the changes to the other dimensions for that VA rating will bring the windings about 3/4" closer to each board and possibly to the caps. It will run hotter due to the idle current losses in the windings as well. Make sure it is shielded as all of the jumper wires used are plated steel along with all of the small signal diodes.
J


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PostPosted: Fri Oct 23, 2015 6:49 pm 
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Location: Toronto, ON, CA
Jaxom wrote:
When I went through all of mine I only had one of the six which actually needed an electrolytic replaced, all of the others measured in spec for capacitance and leakage. The ones I upgraded were all in the signal chain. I found increasing the main power supply caps capacity actually made the amp sound darker, even with 2 smaller bypass capacitors of 47uF and 0.1uF across each.
Good luck fitting larger transformers in the chassis, even if you get one that fits in height the changes to the other dimensions for that VA rating will bring the windings about 3/4" closer to each board and possibly to the caps. It will run hotter due to the idle current losses in the windings as well. Make sure it is shielded as all of the jumper wires used are plated steel along with all of the small signal diodes.
J


Thanks again Jaxom. The transformer will be shielded if I go for a bigger one...


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PostPosted: Sat Oct 24, 2015 5:22 am 
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Joined: Thu Jan 13, 2011 11:29 am
Posts: 694
Location: St.Catharines, ON, CA
Frank,

I believe the Adcom is DC coupled.Rock solid circuit.
The only circuit mods I know of are the bias adjust smoothing cap and the feedback shunt cap.
A dude in the US tart's up the 535/545/555 for the pro studio guy's.

Gary


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PostPosted: Sat Oct 24, 2015 5:27 pm 
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Location: Toronto, ON, CA
sasquatch wrote:
Frank,

I believe the Adcom is DC coupled.Rock solid circuit.
The only circuit mods I know of are the bias adjust smoothing cap and the feedback shunt cap.
A dude in the US tart's up the 535/545/555 for the pro studio guy's.

Gary


Thanks Gary.
535 is indeed a good amp for the price, and solid too. I have fixed/mod some old amps, some of them are also classic and among stereophile top 100 hifi products list, and I probably love 535 more than others.

Actually, I have listened 535 for a while, I reserved my comments on 535 as it's subjective, system dependent, and probably not correct - about 10 years screaming, yelling family life, I lost my confidence in hearing.

Well, I guess it's not a crime to speak out personal opinion, as I did get some canuck members worried. Again, 535 is a good amp, otherwise I won't buy it. In a transparent system, I found it sounds a bit dry/thin, a bit lack of musical, grounding need some work also... I am picky on 535 for sure - as I believe it can do better, besides, I must have OCD, thinking about 30 years elec. caps inside my amp could drive me crazy ;-)

More important, DIY is all about fun, and I value the process more than end result. Having said that, I do not take any DIY adventure blindfolded and unprepared.


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PostPosted: Sat Oct 24, 2015 8:08 pm 
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Location: Toronto, ON, CA
Only have time during nights after children went to bed :(

Now the RCA part is completed...


Attachments:
01_10R3n3.jpg
01_10R3n3.jpg [ 133.97 KiB | Viewed 7397 times ]
02_Paralle10R3n3.jpg
02_Paralle10R3n3.jpg [ 109.21 KiB | Viewed 7397 times ]
03_Sealed.jpg
03_Sealed.jpg [ 100.44 KiB | Viewed 7397 times ]
04_RCAWire.jpg
04_RCAWire.jpg [ 87.57 KiB | Viewed 7397 times ]
05_RCAWire2.jpg
05_RCAWire2.jpg [ 82.87 KiB | Viewed 7397 times ]
06_Solder2RCA.jpg
06_Solder2RCA.jpg [ 92.97 KiB | Viewed 7397 times ]
07_RFCompleted.jpg
07_RFCompleted.jpg [ 112.62 KiB | Viewed 7397 times ]
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PostPosted: Sun Oct 25, 2015 7:40 am 
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Joined: Fri Oct 16, 2009 7:42 am
Posts: 1413
Location: Toronto, ON, CA
Frank, from my limited knowledge of circuits, what you put in seems like a ground lift.
Was it there before? Otherwise what is the reason you put it in?

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