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Old 3rd November 2007, 01:11 AM   #21
BC is offline BC  United States
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Hello Dougie085,

Check polarity of caps, power connections,and in/out signal wiring. Maybe make sure LM3875 pins are in proper holes. Sometimes one can look at something over and over without seeing it properly

Human error vs. bad chips usually wins.

All the best,
BC
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Old 3rd November 2007, 01:16 AM   #22
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Well the wiring is right I checked it at least 10 times. I'll check the caps. The chip I'm not sure how you could put it in wrong?
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Old 3rd November 2007, 01:27 AM   #23
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The capacitors are the same on both boards. And the chips are soldered in the same way too. So I don't think its that.
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Old 3rd November 2007, 01:59 AM   #24
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What is the DC offset in both channels?
Check Caddock resistors if they are in the right spots ( 220 and 22k)
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Old 3rd November 2007, 02:06 AM   #25
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+/- 32.8VDC The amp boards only have 1 resistor on them.
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Old 3rd November 2007, 03:18 AM   #26
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I 'm asking about DC offset (at speaker terminals). It can't be that high.

Also, I see 4 resistors on each amp board in your pics, check if thay all in proper places.
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Old 3rd November 2007, 03:46 AM   #27
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Ok well the channel that doesn't work right has a 22.0kohm resistor on the chip. The one that does work has a 220ohm resistor. This may be part of the problem. I didn't put the actual boards together my self so sorry I didn't realise those were resistors I've never seen a resistor like that. In your manual you use a 22.1kohm so the problem isn't that the other channel isn't very loud its that the other channel is far too loud. Might be where all the noise comes from as well. This makes a lot of sense now. I'll have to see if he has another one of the 22kohm but I don't think the kit came with extra's? So maybe his kit had one of the wrong resistors? I don't know I'll have to ask him about it.
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Old 3rd November 2007, 04:10 AM   #28
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I suspect that resistors may have been swapped. They should be as follows:

R1= 220R
R2= 22k

Rf (directly on the chip) 22k or 22.1k (depending on my stock at a time)
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Old 3rd November 2007, 04:16 AM   #29
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Do you send extra with your kit? The other resistors are correct. So this must have been the last resistor he had in the kit unless you include extra's?
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Old 3rd November 2007, 04:30 AM   #30
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At $4/pc I don't send extras. So far I also didn't make a mistake.

So how many 220R resistors and how many 22k did he have?
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