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

@thecarpathian 

Well, switching implies binary, and with linear amps the transistors or tubes slide smoothly between the rails. 

A faucet, with hot and cold water valves may be a better analogy. 

It's still called an amplifier because the input voltage is multiplied.  Usually by 20. So your DAC through your preamp puts out +-0.1 V, the amp is going to push out +- 2V.

@thecarpathian  :  Your confusion inspired me to put this blog post together about the difference between a power supply and the amplifier sections that go into an amp or other device.

@thecarpathian  Maybe an easier analogy is legs vs. arms. 

You need both to be able to dead lift.

To your weight lifter analogy;

I would liken the weight lifter to the amplifier, the weight he's lifting to the speakers, and the power supply to how much muscle (power reserves) he has.

Theoretically, the more muscle he has (capacitance), the more weight (low impedance speaker) he can lift with minimal strain.

@thecarpathian

No, I would not, because they are really two units and both have to be up to par.

I'd say the muscles are the output stages (transistors, tubes, etc.) and heat sinks.  The power supply is the stage he's standing on.  Both have to be strong enough for the weight. 

I'm adding heat sinks because they are a major enabler for Class A and A/B designs.  You will melt your transistors without adequate heat sinks.  Though truth be told the legal requirements to rate an amplifier n Watts may cause many amps to have exaggeratedly large heat sinks for music playing. 

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

@thecarpathian - kind of sort of. Think of the amplifier as a weight lifter, and the power supply as the stage the athlete stands on. The better the power supply, the stiffer the stand and the better the weight lifter is able to dead lift up to the same point.

The capacitance reduces power supply ripple and attempts to feed the amplifier constant DC  voltages. That is, how much the DC rails vary based on incoming AC and amplifier demand.

Many things go into what the ideal capacitance levels are. Amplifier feedback, speaker load, etc. Generally speaking though, if you want to design a high current amplifier you will need to add more capacitance to ensure it can perform to spec even during high demand.

Should also point out that most amplifiers use linear, unregulated supplies, meaning they are subject to the long term voltage stability coming out of your wall.  Seasons, your neighbors, your HVAC and refrigerator can cause instability even with dedicated lines. 

Your understanding of the electrical formulas are correct.  Impedance curves are most easily obtained from Sterephile reviews, such as this one.  The top chart shows an impedance curve.

This particular speaker shows a minimum impedance ~ 6 Ohms, and IMHO would be a good candidate to be called an 8 Ohm speaker.

I also want to caution you that I've seen dynamic speakers designed specifically to be hard to drive.  They are sold as "revealing of an amplifier's capabilities."  Well, that's great but it doesn't help them play music.

Of course, some speakers just have bad crossovers, and some like the Apogees or electrostatics just can't help it. 

To add to your electrical understanding, amplifiers have an output impedance that is also not usually flat.  Often they are better in the mid to bass than the treble.  That's something else that should be considered.  ESL's are hard to drive in the treble.  A "weak" amp will lose treble output.