Why can't any amp drive any load at low volume? Or can it?

[toroechado]

Hi to all!

Sory if this is too technical but I was bench testing an amp that was capable of delievering 33 V into 4 ohm load. According to my calculations, that is 272.25 watts (P=V^2/R). There should be 8.25 amps (I=V/R). Nice.

Now the question. What if I have a nasty speaker thad drops to 1 ohm at certain frequency but is very efficient, for example 100 dB / W at 1m. As per Crown Audio calculator, such speaker should need 16 watts to listen at 85dB at 4m and with a headroom of 15 dB, that should be pleny.

16 watts at 1 ohm should be 4V and 4A (V=√ (P*R) and I=P/V)... So, if this amp is capable of doing 33V and 8.25A, why won't it be able to put out 4V and 4A? Or can it?

Am I missing something here?

Thanks!

 

[ConradH]

I'm guessing it can, with the caveat of stability and any protection circuit weirdness. One has to look at the SOA of the output transistors, but I have a hard time believing there would be an issue. The problem is you don't want to make a mistake that causes the amp to go to a high output.

 

[prighello]

From my limited understanding, it’s a stability thing. Not all amps are capable of being stable down to 1ohm and will over heat or go into protection mode. If it is just a brief drop most will weather it but if you spend any real time near 1ohm very very few amps will handle that load.

Someone more technical could probably explain but it’s a heat issue for the output stages and the need for current from a stout power supply to be stable into very low impedances. It usually makes for a more expensive amp due to the parts needed.

 

[HPMguy]

Probably a purely academic question, as my understanding is that low impedance speakers tend to be power hogs, not highly efficient. One ohm is pretty close to a dead short, amps with low output impedance will send a LOT of current down the wire and many are not designed for that.

 

[toroechado]

One ohm is pretty close to a dead short, amps with low output impedance will send a LOT of current down the wire and many are not designed for that.

I think that to the amp to send a lot of current there need to be a voltage (signal) level to maintain. And if it’s within it’s capacity, and according to my calculations it is, there should not be any problem. But something tells me that it’s not that simple.

Infinity Kappas are super low impedance but very efficient.

 

[toroechado]

Any other opinion?

 

[charles 1973]

I believe its has to do with too low an impedance regardless of amps power can start an ocilating condition at the output stage that will send any amp to its maximum continuous power avaliable from the power supply. Be it 10w or 1,000. The amps protection circuit should activate to prevent a fire.

Some high curret amps might be able to handle a near short circuit momentarily. This requires very large heat sinks relative to the amps rated power.