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Old 1st February 2006, 09:41 PM   #1
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Default Sonic Impact T-Amp Oscillating at ~5hz

I just got a pair of sonic impact amps, and for some reason, I'm having oscillation problems at higher volume levels. Is this the over-current protection kicking in and then cutting out? It happens on both of my amps, of which, one is modded for the "stealth" input and the larger tank capacitor, and one has only the larger tank capacitor. It only happens when I get to a certain volume level, then it does the weird pulsey thing, and I freak out and turn it back down. I have to turn it down quite a bit for it to go away. So there's some hysteresis in the cause.

I have a couple ideas as to what the problem is, one of which would be the protection circuitry, and the other is the power supply. The power supply I'm using right now is a 4A 12V SMPS hijacked from my LCD panel. Any ideas? Thanks.
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Old 1st February 2006, 10:00 PM   #2
Pano is offline Pano  United States
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If the amp is actually cutting off and back on, it's overheating. If it's just pulsing, I don't know. There is a lot of over current and over temp protection.

Anyone else have this problem?
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Old 1st February 2006, 10:20 PM   #3
BWRX is offline BWRX  United States
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Do you have a little wall wart or regulated supply you can test the amps out with? Me thinks you might be seeing some sort of stability issue with the SMPS since you get the same problem with both amps and no one else has ever reported such an issue.
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Old 2nd February 2006, 12:37 AM   #4
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It wasn't too hot to touch. Might be overheating though. It might be the power supply. It's an smps, but I have no idea about the specs. It's a strange sound. Might be cutting in and out, or a pulsating. Because it's so slow, I think it's probably the power supply. I'll see what happens when I hook up my real supply. If I have problems like this again, I'll try putting a resistor in series on the line. Anybody ever heard of this before?
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Old 2nd February 2006, 01:33 AM   #5
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Sadly, I don't have another 12V supply to try. I think maybe the control circuit for the SMPS is unstable into the amp. Does this sound like a possibility? Hopefully it won't be a problem with my SMPS that I'm going to use in the final setup. I've got a lot of capacitance on it, so the time constant should be pretty slow. But capacitors are reactive, so that might cause more instability. I'll see.
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Old 2nd February 2006, 03:37 AM   #6
Pano is offline Pano  United States
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Just get a 12V battery, or 2x6V, or even one of those battery holders at Rat Shack.
10 AA or C or D in series will give you the 12V you need to check it with.

Thinking more about it, - could be the power supply that is cycling in and out of over-current protection. Most SMPS have over current protection. Could be that.
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Old 2nd February 2006, 03:40 AM   #7
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I should just take it to my car... open up the hood...

sacrifice the transportation for debugging.
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Old 2nd February 2006, 04:56 AM   #8
Pano is offline Pano  United States
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Quote:
Originally posted by philibuster
I should just take it to my car... open up the hood...
Ha! Funny!

BTDT. But it was a blown PSU in a theater ligthing board. Had to do it every night for a week. "Lighting by Volvo".
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Old 2nd February 2006, 07:13 AM   #9
el`Ol is offline el`Ol  Germany
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I had similar problems, less extreme, which resulted in bad timing. I found out that the variable voltage analog power supply was the cause. Probably the SI has a circuit that prevents weak supplies from overpower and the two voltage regulations caused the oscillation.
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Old 2nd February 2006, 08:46 AM   #10
dnsey is offline dnsey  United Kingdom
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Remember to use a fuse - car batteries don't have overcurrent protection
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