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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 21 Mar 2009, 22:18 
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Location: Austin, TX
Here is the ExpressPCB file that I created for the amp.
Attachment:
Adcom-GFA-535-PSU-PCB.png

:cop: See Adcom GFA-535 PSU Rev. 2 Gerber Files for the latest PCB design

A few things to note:

1) I've not yet tested this board nor have I had a chance to ensure that it will install correctly in the amp. I'll post notes as I get everything in place to do this. I have everything except the pcb at this time.

2) The default amplifier has two sets of speakers, A and B. Since I never used the connections for B, I eliminated these connections from the board in order to allow more space for larger caps.

3) This board will permit up to 35 mm caps, but note that the 535 has a small chassis and the tallest cap you will be able to install is 50 mm in height.

4) The original board had twist type pressure connectors, but my revised board will allow you to pick your favorite exotic or non-exotic chassis wire. I will be using a 16 gauge wire, but the stock Adcom uses 20 gauge. YMMV


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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: 22 Mar 2009, 10:04 
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Location: Winnipeg, CANADA
Look good. Are their rates reasonable for low quantity purchases?

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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 22 Mar 2009, 17:02 
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Gio, I was surprised at how high the board price is for this project. I used the auto-quote feature in ExpressPCB and it is a min of 2 boards for approximately 86 USD total.

I found a seller on ebay from Croatia who would build a single board for $26 USD, which I ordered two weeks ago. The board still hasn't arrived after a promised ship date of March 6th. He's been responsive to my emails and I'm hoping that it has just been delayed in the email.

I noticed that Futurlec also provides a proto board service. When I ran some raw numbers on their calculator, the board comes out to $35 USD, which is not too expensive.

I found a board shop in China that seems desperate to capture some business in the US and he offered to build it for free if I give him positive pub on diy forums.

Other than that, I thought about etching a board myself, since I did that in my younger days with a Radio Shack kit. However, I can't find that kit anymore on their website. It seems I'll have to invest about $100 USD to get set up with an etching kit.

Do you have sources in Canada that could do this cheaper?

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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: 22 Mar 2009, 17:07 
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Gio,
Thanks for tweaking the psu file a bit. It dawned on me last night that I had both rectifier silkscreens reversed. Someone might have mounted them backwards. Ugh!

Everyone: on the psu board, the central screw mount is the star ground. It is the sole point that is attached electrically to the chassis.

Here are the schematic diagrams.
Attachment:
Adcom-GFA-535-Aplifier-Scheamtic.jpg


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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: 22 Mar 2009, 18:00 
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No cheap sources up here for low quantity PCB purchases. I still have a couple of the Radio Shack kits and the ones I make are old school drawn out by hand (literally, that's how I did them in school!). But most of the time I just revert to a protoboad.

Cheers

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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 22 Mar 2009, 20:39 
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Well, I just finished resoldering the leads for all the transistors attached to the heatsink on the right channel. I think this is really worth the effort if you find the same poor level of workmanship in your Adcom.

I soldered several leads that were floating above the pcb pad and in one instance, the lead was not even above the pad, but just off the pad by a millimeter. I could see where the worker had flowed and reflowed solder to get enough to connect lead to pad electronically. Plus, there was so much solder, I ate up a good portion of the 10 ft. of solder braid.

From my previous employment, our tech said that there should not be gobs of solder on a pad but that there should be a fillet between lead and pad. I think I have a few boards in the garage that I can fish out and show what I mean.

I'll post a follow up photo soon and you can see I was much less enthusiastic with the soldering gun.

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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: 22 Mar 2009, 21:26 
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Question: the trimpot on the schematic is a 2.2k cermet single turn version. Can I get with with a 2k (25 turn) trimpot?

I assuming the critical point is the voltage measured at the test points, correct?

Here's the link: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=490-2918-ND

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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: 23 Mar 2009, 11:47 
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Can you check the existing pot and see what it is set at? If it is well below 2k, I would go for the multi-turn pot.

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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 23 Mar 2009, 11:49 
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Gio, I measured 1.6k/.6k out of circuit. I think that 2 kOhm should give me enough. Sound good?

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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: 23 Mar 2009, 12:05 
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Yes ;)

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