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 Post subject: Bad solder joint
PostPosted: 02 Apr 2009, 21:50 
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Joined: 11 Dec 2008, 10:23
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Location: Austin, TX
I mentioned this in the thread regarding soldering, but here is a photo of what happend when I adjusted a resistor on the left channel.
Attachment:
badsolder.jpg
The pad is still intact, just oxidized. :down:


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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: new psu board
PostPosted: 02 Apr 2009, 21:55 
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Here is the new psu board with components installed. Note that the first revision does not have snubber caps. The second revision I have almost completed and will contain locations for the snubbers. I had to increase the diameter of some of the through holes with my drill, which accounts for the residue/dust on the components and board.
Attachment:
psunew1.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: 02 Apr 2009, 22:07 
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Looking good! :up: Will you A/B the difference between the snubbed and no snubber PSU?

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PostPosted: 02 Apr 2009, 22:14 
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From the rear view of the board, I designed it too tight to the back side of the chassis and I had to pull out my dremel tool to remove a bit off the back edge of the pcb.


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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: 02 Apr 2009, 22:17 
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Gio,

Ha! Yes, I'll definitely be doing the A/B thing. I promised the wife that I should have the amp running within the week, so I'll be able to demo w/o snubbers. When I get the revised board done (and I'll upload the file for anyone interested), then I'll try out the version w/snubbers. If I don't like the sound, then I'll just clip out the snubber 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: 16 Apr 2009, 13:15 
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Hello Folks:

Well, the wife, myself, and 3 of 4 kids all got sick with a big Texas virus! It was one of those 2 week jobs that really puts you in a funk! I got nothing accomplished and me and the wife have been busy putting the house back in order.

I've got some news to report and I should have a new posting this weekend. I redesigned the psu board to not only accommodate snubber film caps but also snubber resistors across the caps. I had to find the smallest available resistor in 1/4 W range and they will have to mount on the underside board, but it was doable.

I will post an image for those who love to etch your own board, as well as Gerbers if you don't mind spending the dough and having a shop build one for you.

Key features of the new board:

1. snubber caps and resistors across the bridge rectifier (optional)
2. can accommodate 35 mm diameter caps (up to a max of 50 mm in height)
3. Silkscreen with reference designators
4. Wide traces like the original
5. Power, Ground, and Signal connections to PSU are silkscreened with designators from the stock board
6. Approximately 12 mm of clearance from the back of the power caps to the back of the chassis
7. Additional mounting holes (total of 5) to stabilize the board to the chassis.
8. Through holes to accommodate up to 16 gauge wire
9. Capacitor polarity clearly marked

Other things on my "To-Do" list:

1. Create a BOM with part sources
2. Create a "How To" list of things to consider when replacing the stock psu w/this modified version.

Stay tuned.....

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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: 17 Apr 2009, 07:37 
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Glad to hear you are better. Is 1/4W sufficient? The original resistors looked like they were in the 2W range.
Cheers

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 Post subject: Re: Adcom GFA-535 rework
PostPosted: 17 Apr 2009, 08:52 
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Gio,

You are correct about the 2 W resistors. They bridge the big power caps and I've left plenty of room on the top side of the board for them.

The snubber resistors will bridge the rectifier. According to the Hagerman article on RC snubbers, the resistor at that point has to handle uW of power. There will be 4 of these resistors to span each diode of the bridge, so to speak.

Also, in the new layout, I've positioned the 2W resistor and the filter cap so that it is more in keeping with the schematic. The stock board had the resistor and film cap "downstream" near the B+/B- output.

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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: 17 Apr 2009, 18:37 
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Thanks for the heads up on that article - I had not seen it before. For those interested in the article, here is the link: http://www.hagtech.com/pdf/yoke.pdf
Attachment:
Calculating-RC-Snubbers-for-Yoke-Damping-Jim-Hagerman.pdf


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PostPosted: 18 Apr 2009, 09:29 
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Location: Austin, TX
Folks,

Here are the updated Gerber files. To print them out, you will need a Gerber viewer. I used FreePCB and it does not have a print feature, so you will need another app to do this if you want to etch your own.

You can try this one - http://www.pentalogix.com/
Attachment:
adcom535 psu.zip

I'll ask Gio to drop the original because I don't think it will work too well because the big caps are too close to the back of the chassis for my comfort. - :cop: - done 18 Apr 2009 - GM

One minor question that I have is that the large copper areas on my redesign are filled with thermal reliefs to aid good solder joints. I had a concern about using thermal reliefs on the big caps where currents can be high. I researched on DIYAudio.com but didn't see any comments raising large concerns over this. I don't know if anyone here has an opinion.

If I have time this weekend, I'l put a BOM together to aid in your parts buying decision. A reminder that the snubber caps and resistors are optional. These are the total 8 pairs connected across the bridge rectifier. The 2 other pairs (C9 to C12, R1, R2, R12, R13) are NOT optional, since they are part of the original design.

I will post a comment this weekend if a Rev. 3 is needed. The fit is tight and I would like to be sure that the board won't introduce any complications. Of course, once I have board in hand, I will post photos of the installation, as well as my impressions of the sound before, after (no snubbers), and after (w/snubbers) and which I prefer.


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