Low amps cause my amplifier to smoke?

You could connct it to a 12V battery in series with a headlight bulb. If the quiescent current is low, the lamp will not be bright.

If the lamp is bright, measure the voltage across the radio. If it is very low then there is a short inside. Check for any hot components.

 

Darned right, duke 37.
I've often used an incandescent lamp in the place of a fuse when I wasn't sure what
was going to happen in a circuit. A fuse just pops. A lamp in series handles the current,
and allows you to find the problem in the circuit.
Great suggestion here.

 

The problem that caused the smoke was probably the current limiting action of the power supply. As the current begins to exceed what the supply can handle the voltage will be throttled back in an attempt to maintain a constant current. As this happens, the internal circuits of the amplifier will not longer be under the voltage conditions they were designed and poor old semiconductors really don't like that.

My bet is that smoke was silicon. I've had a lot of FETs find the way out of their packaging leading hardly any trace.

As mentioned before you should be using a power supply capable of nearly 1.5 times what you're expecting to use it for, but in particular with audio the RMS power is really drawn in low frequency chunks, think the beat of the music, these extra chunks have to come from somewhere and typically be too low a frequency for the decoupling caps to smooth. (Just though this could be a useful note (that is seriously not a pun).)

 

Now, I would advise initially connecting the bulb in series, that way under no real load (just quiescent conditions) the amp *shouldn't* be drawing too much current and the bulb will present very little barrier (the resistance of a bulb is very low at low current remember). If however there is now a fault that will cause excessive current the bulb will light.

Assuming that the bulb does not glow, before actually amplifying anything, short out the bulb, this will prevent any undesired under voltages.

I am in no way certain that an under voltage would have damaged your amp, but I have had a few rare cases where similar has happened. Current limits from power supplies also have a tenancy to causes funny oscillations when you start drawing current close to the limit, that could also be a possibility.

 

You do not give details of the amp however, at low output powers the current drawn should be very low and the bulb would not light or just glow.

Consider a drum, to get sound out you have to give it a thump with a stick to put energy in. An amplfier has to provide an electrical thump to the speaker to reproduce the sound. Power amplifiers will not take much power when they are not driving the speakers hard so start with the volume at zero and go gently.

If the power supply cannot provide the peak current the amplifier requires then the signal will be clipped and you will get distortion.

If smoke has come from the amplifier it seems to me that it is likely to be damaged.

The bulb trick is very useful to find shorts in vehicle wiring.