Sonic Impact T-Amp Oscillating at ~5hz

Status
Not open for further replies.
Jump to Latest
P

philibuster

Member
Joined 2005
#1
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.
 
#3
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.
 
#4
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?
 
#5
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.
 
#6
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.
 
#9
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.
 
#13
AFAIK there is no DC protection circuit, as many here have found out the hard way.

There is overcurrent and overheating protection, tho. A massive DC offest would cause either of those faults, given enough time.

A very large subsonic signal running at max power could also cause it, just like anyother max power signal. But with the subsonics, you might not know its there.
 
#14
I was playing my vinyl, and the record was a little warped. I've looked at the waveforms before, and I have this large resonance of the arm at a very low frequency. Probably has something to do with it.

So... no dc protection... maybe what I was hearing was some ridiculous clipping when the waveform went high and low due to the slow resonance of the arm/cantilever.
 
#15
philibuster said:
I was playing my vinyl, and the record was a little warped.
Click to expand...

Ah Ha!! That could well be it! You know that the RIAA curve puts a mean boost on the bass.

I remeber building my 1st tube RIAA preamp. Sounded fanastic, but had no bass stop. I noticed my drivers riding waaay in and out with the tone arm movements.

Maybe that's what's been going on with your amp.
 
Status
Not open for further replies.
Top Bottom