Amps, output power, Ohm rating

[jinjuku]

I have been reading up on amps and output and ohm sensitivity.

So my question is this:

Amps have a total output of say 42 volts and is lets say 8ohm stable. Even if you put a 4 ohm load your ok as long as you don't go over 42 volts (from the transformer)?

So I could place any load sensitivity on an amp and as long as it doesn't exceed the output capability of transformer?

Thx

 

[Haoleb]

Im going to try and answer this for you the best I can without getting too complicated here, The power transformer doesnt have anything to do with actual amplifier capabilities and output power. In a way. If it is undersized and cannot provide the required current needed by the amplifier section it will only limit it but it doesnt directly correlate to actual power.

In regards to how low of impedance a speaker an amplifier will drive, this is mostly determined by the current output capabilities of the amplfiier section. A lower impedance will require higher amounts of current so if the amplifier cannot provide those it will shut off due to overheating or overcurrent protection circuits kicking in.

So lets say you have an amplifier hooked to 8 ohm speakers, It can drive them to loud levels without a sweat. Hook up 4 ohm speakers and it starts to sweat some more and gets alot hotter, hook up 2 ohm speakers and try to drive them to those same levels and you might trip an overcurrent protection and you'll most likely trip the heat protection after everything gets too hot.

Its too general to say you could place any impedance on an ampliifer, Its better to assume you can place any load on an amplifier that it has been rated for. And as some people have found out with certain amplifiers even that isint the case.

with regards to your voltage question, its like this. Voltage isint as an important factor to look at as is amperage. For example take a standard 15a wall outlet, When you hook up too many things you arent "going over 120v" your going over the 15a that it is capable of supplying and the circuit breaker trips.

 

[TLS Guy]

I have been reading up on amps and output and ohm sensitivity.

So my question is this:

Amps have a total output of say 42 volts and is lets say 8ohm stable. Even if you put a 4 ohm load your ok as long as you don't go over 42 volts (from the transformer)?

So I could place any load sensitivity on an amp and as long as it doesn't exceed the output capability of transformer?

Thx

The stability of the amp under conditions of dropping impedance is determined largely by the deign of the output stage and how robust the power supply is.

A poor amp will deliver 42 volts into 8 ohms, but drop the voltage into four ohms and halve the power available. This is the typical situation for a lot of receivers. A good amp will maintain the 42 volts driving the four ohm load and double its power output.

Be careful of loudspeaker manufactures impedance specs. They are largely fiction, and "nominal impedance" means nothing. If there is more than one woofer, you can go to the bank that it is four ohms or less, to all intense and purposes, no matter how the manufacturer rates it. A single woofer speaker can also drop its impedance below 400 Hz due to diffraction compensation in the crossover.

 

[PENG]

I have been reading up on amps and output and ohm sensitivity.

So my question is this:

Amps have a total output of say 42 volts and is lets say 8ohm stable. Even if you put a 4 ohm load your ok as long as you don't go over 42 volts (from the transformer)?

So I could place any load sensitivity on an amp and as long as it doesn't exceed the output capability of transformer?

Thx

TLS covered the role of the output stage of the amp. I would like to add that even if the amp can handle double the current demanded by half the impedance, if the load current exceeds the full load rating of the transformer you will still end up not getting the power. That is because the transformer will not be able to maintained the voltage. The voltage output from the secondary winding (the low voltage side) could drop drastically if it is overloaded by a wide margin.

 

[highfigh]

I have been reading up on amps and output and ohm sensitivity.

So my question is this:

Amps have a total output of say 42 volts and is lets say 8ohm stable. Even if you put a 4 ohm load your ok as long as you don't go over 42 volts (from the transformer)?

So I could place any load sensitivity on an amp and as long as it doesn't exceed the output capability of transformer?

Thx

Look at Voltage as water pressure (psi) and Current as flow rate (gal/min). If you have a good supply, your pressure will stay high, even though you opened the valve more and the flow has increased. Electrical current measurement is actually an indication of how many electrons move in a certain amount of time, to be more technical. A beefy power supply is similar to what's on a fire truck and a weak one is like a sump pump. They both move water but one is made for more volume.

 

[fmw]

TLS is correct. The power supply has very much to do with an amplifier's ability to deliver current. Better amplifier designs do a better job of dealing with low impedances. No doubt about any of that.

I'm going to tell you, however, that most amplifiers are conservatively rated in terms of their ability to drive low impedance load. They are so rated primarily for legal reasons because we all know that audio component manufacturers love to stretch their specs. This is one spec they don't stretch because, at the extreme, it can result in equipment damage, not just a failure to meet a spec. Personally, I have not encountered an amplifier that won't drive a 4 ohm nominal load to normal listening levels without overheating or distortion. I'm sure there are some, but I haven't encountered one. I've tested scores of them over the years. Yes, it is always possible to abuse the equipment-exactly what the lawyers are concerned about. I'm talking about normal use. Except in extreme situations, I wouldn't spend much time worrying about it. I've heard my own 6-ohm-minimum-rated receiver drive electrostatic speakers to very loud levels without clipping (o-scope measured.) Those speakers dip below 2 ohms at some frequencies.