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Old 13th November 2006, 02:27 AM   #1
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Default Can't get home built amp working

Hello,

Over the past month or two I've built myself a 50w/ch. stereo amplifier, but I can't get it working. It is Randy Slone's "pro 60" design. I keep blowing rail fuses, but I have failed to find anything shorted, or even close. I've gotten some interesting data points, but I can't make any sense of them. First the negative rail blew a filter cap and fuse. I removed the blown filter cap and put in a new fuse on the negative rail. When I did that it blew the same filter cap on the positive rail and the positive rail fuse. So I removed that filter cap too. After that it blew the negative fuse, but not the positive one. Also the speaker output is at the positive rail potential. So, my thought on why the caps would blow was that they were reversed polarized; they are right on the board, but maybe I had my supplies backward. They didn't meter this way, but I went ahead and tried switching them anyway. Just like before the negative side fuse (really positive now) blew while the positive side (really negative now) did not. Again the output was at the positive rail potential (really negative potential as measured to circuit common). So, I am thoroughly confused as to what could be going on that would allow the circuit to be flipped positive to negative with no change in what's going on.

Thanks for any help you can give me,
Alex W.
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Old 13th November 2006, 02:51 AM   #2
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Default Re: Can't get home built amp working

Quote:
Originally posted by ackeron42
Hello,

Over the past month or two I've built myself a 50w/ch. stereo amplifier, but I can't get it working. It is Randy Slone's "pro 60" design. I keep blowing rail fuses, but I have failed to find anything shorted, or even close. I've gotten some interesting data points, but I can't make any sense of them. First the negative rail blew a filter cap and fuse. I removed the blown filter cap and put in a new fuse on the negative rail. When I did that it blew the same filter cap on the positive rail and the positive rail fuse. So I removed that filter cap too. After that it blew the negative fuse, but not the positive one. Also the speaker output is at the positive rail potential. So, my thought on why the caps would blow was that they were reversed polarized; they are right on the board, but maybe I had my supplies backward. They didn't meter this way, but I went ahead and tried switching them anyway. Just like before the negative side fuse (really positive now) blew while the positive side (really negative now) did not. Again the output was at the positive rail potential (really negative potential as measured to circuit common). So, I am thoroughly confused as to what could be going on that would allow the circuit to be flipped positive to negative with no change in what's going on.

Thanks for any help you can give me,
Alex W.
Two questions:

1. Is your supply working alright?
What Volt DC does it produce, if you try it WITHOUT amp?
And is this Volt DC pure DC, with very little AC ripple?

2. What Voltage Rating has those Electrolytic capacitors got?
Say your supply is 2 x 30 VDC.
Then It is good if caps are rated 40-50 V.
Are those capacitors really connected between V+ and GROUND = earth level?
And V- and GROUND.

Maybe they are connected between V+ and Amp Output ....


I don't think it is supply / capacitors that is main issue.
This is only the symptom.
The amplifier is somewhere else put together wrong.
Or not initially adjusted correctly.


Because if correct, than output voltage should be at 0 Volt level.
- Read the final setup instructions
- Make a new check up of everything is connected as in schematic.

Randy G. Slone Kit amplifier should not have no such problem.
There are 1.000 of such kit built and delivered.
They should be safe and good working.

lineup
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Old 13th November 2006, 06:04 PM   #3
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you may have blown transistors, either via overheating with soldering, plain dud ones, or via connecting the psu's the wrong way around.
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Old 13th November 2006, 06:35 PM   #4
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hello, have you checked the output transistors are in the right way round? N & P ?
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