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Old 2nd April 2012, 06:21 AM   #121
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Rear panel progressing. Need to find some RCA jacks that will work for the wood panel. The ones I have require some hogging out of the panel and won't leave much meat behind. Might machine a sub-plate instead if I can't find a suitable jack. There are some neutrik ones that will work but I won't pay for shipping for such a small order since I'm a cheap ***. So, a sub-plate may be the solution...

Click the image to open in full size.

Still trying to figure out how I'm going to test the channels independently. I may end up with a couple connectors... I have some of the larger molex connectors that would work fine. In retrospect, a couple terminal blocks on the PSU PCB may have been a good idea. Ah, hindsight.
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Old 2nd April 2012, 07:53 AM   #122
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Nice tread
My 2 C about the imputs

Why not XLR they are there if you going to make balanced one and work fine for mono
Neutrik barrel type will fit nicely troug back pannel
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Old 2nd April 2012, 08:11 AM   #123
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I do believe CARDASS make some long thread RCA jack. Check them out.
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Old 2nd April 2012, 01:35 PM   #124
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Quote:
Originally Posted by oneplustwo View Post
Might machine a sub-plate instead if I can't find a suitable jack.
Probably a good idea. The wood looks nice, BTW.

Also, convention says that you put the black (grounds) of the speaker output posts in the center, so they are mirror-imaged.

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Still trying to figure out how I'm going to test the channels independently.
Unsolder the amp board's power wires at the PSU. Test the PSU. Re-solder one channel, test, bias. Re-solder the other one, test, bias. Then set final bias. Done!

Last edited by 6L6; 2nd April 2012 at 01:46 PM.
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Old 2nd April 2012, 05:18 PM   #125
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I was wondering how that should work... makes sense given the grounds will go back to the PSU PCB in the middle of the chassis anyway.

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Also, convention says that you put the black (grounds) of the speaker output posts in the center, so they are mirror-imaged.
PSU is tested and reads 24.3V +/- on both sides so good to go there. I guess I can test one side independently and assuming that's fine, go ahead and test the other one without disconnecting the first.
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Unsolder the amp board's power wires at the PSU. Test the PSU. Re-solder one channel, test, bias. Re-solder the other one, test, bias. Then set final bias. Done!
Also, I got my bulb tester wired up with a little clip on lamp that has been sitting unused for years. Yet another piece of "scrap" used for this project! Does it matter what wattage bulb to use? I tested it with just the PSU and as expected, it lit up briefly.
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Old 2nd April 2012, 07:02 PM   #126
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If you use a 100w bulb (incandescent) it should limit the AC if there is a major problem.

Did you test the PSU voltage in the amp case as well?
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Old 2nd April 2012, 07:06 PM   #127
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Yup, tested the PSU in the amp case as well. Decided to use the thermistor as part of the PCB as well for simplicity sake if nothing else.

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If you use a 100w bulb (incandescent) it should limit the AC if there is a major problem.

Did you test the PSU voltage in the amp case as well?
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Old 2nd April 2012, 07:16 PM   #128
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Great! Hook up one of the amp channels. Turn it on with the bulbtester. If the glow is similar to what you saw with the PSU, then disconnect the bulbtester and power it up. Bias to .5v and zero offset.

Lather, rinse, repeat with the other side.
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Old 2nd April 2012, 07:18 PM   #129
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hee the way i did it. fire up the PSU's. connect one amp. adjust bias and offset to little over half my goal. let it warm up. adjust to final setting. wire up next amp and adjust that one while the first amp played on a test speaker.

PS: don't bother with 0V offfset. you will need to readjust after a while anyway.

Last edited by AudioSan; 2nd April 2012 at 07:22 PM.
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Old 2nd April 2012, 07:32 PM   #130
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BTW, for whatever reason, the rising resistance thing went away when I disassembled the pieces and re-measured. They now are at 0 ohms. For the record, I put them in backwards as evidenced by the fact that I had to turn them fully CW to get the reading to zero.

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Yes, Bourns. The confusion is whether I installed backwards or not.

Weird. When I measure across the resistors, the values slowly rise till I get an open circuit. Is that a problem with my cheapo DMM?
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