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Old 10th December 2005, 05:49 AM   #1
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Default Sonic Impact Troubleshoot

I am running into problems modifiying my sonic impact amp, and so I purchased another one in hope of finding the problem. I ran into the exact same problem of 12 volts running through the speaker line in my second sonic impact amp. What would cause 12 volts to run on the speaker outputs? The mods I tried on both amps are running 12 volts directly to the power supply pins. Replace the inductors with air core, replace diodes, connect two black gate caps on the 12 volt line. I am so frustated right now with not being able to find the problem.
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Old 10th December 2005, 06:01 AM   #2
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Well I guess the obvious thing to check would be whether somehow the 12v wire got hooked up to the output somehow. I doubt this is the case as I am sure you attached the power where is was supposed to go. Hmm, make sure your diodes are in the correct direction, etc... I have heard of several doing these mods with no problems.

What you should probably do is reverse all of the mods, then test it making sure it is operating normally again, then apply a single mod, test, next mod, test, etc... You may be able to narrow it down at least. Sorry I cant be of too much help, just some thoughts to consider.
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Old 10th December 2005, 06:54 AM   #3
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It can be tough to find. I just killed one last night. It was working fine with Blackgate input caps, when I switched them out for film caps- bing! 12V on the outputs. I can't even see why, other than there is now no 2.5V on the input caps.
These little things are fiddly, that's for sure.

Check to see if you have 2.5 volts on the chip side of the input caps. If not, there may be a short or miswire there somewhere.

BTW, why change the diodes?
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Old 10th December 2005, 02:47 PM   #4
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I don't see how the input caps play a role in 12 volts going through the speaker outputs. I upgraded to sonicaps and with them connected or disconnected I still get 12 volts running through the speakers. It just blows my mind on what went wrong. I connected up everything through pc mount and mini jack and everything worked fine. It wasn't until I desoldered the C3 and C4 caps that I am now running into problems and connecting the 12 wire to the pins of the chip. These seem to be the newest revised boards and quality is such a diminishing factor. Thanks again, Kevin.
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Old 10th December 2005, 06:31 PM   #5
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Hey Kevin,
It's not the caps themselves, it's the input circuit.
The reason the caps are there is because the inputs are biased to 2.5 volts. This bias is needed for the following circuit to work correctly. The caps are there to keep the bias voltage in.

What happens when you don't have 2.5 volts? Any deviation from that 2.5 gets amplified at the output, that is the amplifiers job, after all. The offset gets amplified about 18X in the Sonic, so it would take less than a volt off at the input to give you 12V out.

The input bias may not be your problem, but if it is off, you will get massive DC out. (sniff, sniff - what's that smell?) It's the 1st place to check, anyhow.
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Old 10th December 2005, 08:40 PM   #6
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How exactly do I fix this problem than? Does it mean my amplifier board is fried? Sometimes I get a nasty smell right when I turn on the amp and it doesn't work all together, but that was with a different sonic amp board. Thanks for your time in this matter, Kevin.
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Old 12th December 2005, 02:44 PM   #7
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I am not getting any voltage on the input capacitors. If the amplifier is working normal will I still get 2.5 volts at C3 or C4 if the caps are desoldered? I have already gone through five amplifier boards and the frustration is killing me. I have done four boards sucessfully and they were my first ones! I don't smell anything bad when I turn on the amp just the a big thump of 12 volts running through my speaker outputs.
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