Question about high current amps versus "not high current amps"

simplest test of amp current handling adequacy is to tap low frequency. driver membrane and checking voltage waveform at speaker terminals with the scope.. if voltage amplitude p-p observed is more than 10mV, then need to check speaker connectors, cable, amp relay contacts, and then try higher current amp design to see if it helps!

@westcoastaudiophile  This does not show if the amp is 'high current' or not. It simply shows if the amp has a low output impedance (if yes, is able to damp the EMF thus generated).

@tomrk I offered a good metric earlier; whether or not the amp can double power from 4 to 2 Ohms.

Therefore, my conclusion is slew rate is important to SQ, though not as much impedance matching, To the physicists and electrical engineers, is my conclusion valid?

@jsalerno277 No. Its a lot more complicated than that. Slew rate is only one of 40 or 50 variables that make up sound quality. There are some excellent sounding amps that have very low slew rates.

"Low Current" amplifiers (though nobody calls them that) will NOT produce more power into the dips - though in practice they are affected, and will produce some amount that is more or less depending on numerous factors. But they typically will NOT come close to "doubling down". These amps are also called "power sources".

@mulveling This statement is incorrect. You could be referring to a tube amplifier in this. Tube amps, if imbued with enough feedback, can behave as a Voltage source yet won’t double power when presented with a load of half the impedance. Instead, they will cut power in half when presented with a load of double the impedance. If the tube amp has no feedback, then it will behave more like a power source although it will be only roughly so. If the amp has both current and Voltage feedback and the two are balanced to the same amount then the amp can behave as a true power source. If you did this with a solid state amp it would behave that way too.

At any rate, a tube amp with enough feedback can drive a variable impedance test load with minimal variation- around 1/10dB, yet no tube amp is considered ’high current’.

A better model for a ’high current’ amp is one that can double power from 4 Ohms to 2 Ohms. Whether that’s of any help with most speakers is highly dubious; any power amplifier will sound better (have lower distortion) if its not having to work hard for a living!

@thecarpathian 'Output devices' means components in the output section of the amplifier; usually power transistors mounted to a heatsink. We make both class D amps and tube power amps so in their cases either GaNFETs or power tubes.

so what might be the instantaneous currents provided in music reproduction, even for a few milliseconds? 

@mclinnguy The instantaneous power will be within the output power limit of the circuit. Therefore so will the current (else the amp fails or goes into protect mode). Generally speaking its not that much! On a 4 Ohm non-inductive load 200 Watts will produce roughly 7.07 Amps (200 = 4 times the current squared; IOW the square root of 50). If there's a weird phase angle involved with that impedance in a nutshell it will behave as if the load impedance is lower. So if similar to 2 Ohms then the current is 10 Amps.

So you can see all these wild current claims are not having to do with output power that's actually driving the speaker.

I’ve always thought the higher capacitance reserve an amplifier has, the more amps it can deliver when needed. This isn’t correct?

@thecarpathian That isn't correct. By that metric our MA-2 can deliver more amps that most solid state amps of the same power. The output power is determined by the power supply Voltage and the resulting current that the output devices can handle. So that has a lot to do with the power transformer and the dissipation the output devices will see. In short- its complicated.

@mclinnguy This statement is false:

A Coda 16 has 280,000 uF of capacitance and can deliver 100 amps of current, per channel.

Here’s why. As @immatthewj points out, the power the amp makes is equal to the current times Voltage. The actual Power formula is 1 Watt= 1 Amp x 1 Volt; IOW power is equal to Volts x Amps. A derivative of this formula that includes Ohms is Power= Ohms X Amps squared.

Giving the Coda the benefit of the doubt, that it can drive a 1 Ohm load, at that impedance the power is equal to the amperage squared. So I think you can see the Coda, as good as it is simply can’t do that; that’s 10,000 Watts! That sort of current through the output section of the Coda would heat the output devices to slag.

That value is actually the amount of current that flows when the power supply is shorted for 10milliseconds so has nothing to do with output power nor the impedance it can drive.

My take;

If you’ve got a bunch of big honkin’ capacitors in your amp, you’ve got a high current amp.

@thecarpathian Please read my above explanation about why this isn’t true. The reason to have lots of capacitance in the output section is to prevent the amplifier from modulating the power supply which can introduce IMD. It has nothing to do with the output power otherwise. We make some amps that have large 3" diameter caps which have a lot of storage; as much as any solid state amp of the same power. But being tube amps they are not likely to be considered ’high current’.

What is important for most speakers is that the amp can behave as a Voltage source; IOW that it can produce the same output Voltage regardless of the load impedance. No amp can actually do that of course but over the range of impedances most speaker present there are quite a few amps that do behave as Voltage sources on them.

But to be clear a tube amp can behave as a Voltage source too as long as it has enough feedback to allow for a low output impedance. But instead of doubling power as impedance is halved it cuts power in half as impedance is doubled.