Digital Amplifier Questions

Ok, now I remember why I can't get this...

Can someone dumb it down for me as far as Class A, Class A/B, Class D?

I really only know that Class A amps are usually lower wattage, inefficient (whatever that means aside from drawing more electricity from the outlet...), run hot, but sound good (right?).

Class A/B is some type of dual mode where it runs in Class A for the first few watts then switches to Class B? Now this doesn't really make any sense to me. Wouldn't the transition be audible?

Then Class D... some type of switching amp, where it switches on and off? This makes no sense to me either. And why the heck did I think it was a Digital amp?

Anyhow, when I go to research what a Class D amp is, or any amp/preamp/dac/electronics, my research instantly turns into me looking up 15 words in the first paragraph which leads me to look up 100 more words, trying to wrap my head around it all, then steam comes out my ears and I start twitching.

I'd like to have a better understanding of all this so maybe someone can describe it in layman's terms?

PS, Thanks Mapman for your input. I've noticed you've been raving about your Belcantos for awhile now, not quite as much as ohms, but close! Good to see you enjoying the setup

I'll try the most basic explanation.

I really only know that Class A amps are usually lower wattage, inefficient (whatever that means aside from drawing more electricity from the outlet...), run hot, but sound good (right?).

The output is always on driving both the positive and negative side of the signal.

Class A/B is some type of dual mode where it runs in Class A for the first few watts then switches to Class B? Now this doesn't really make any sense to me. Wouldn't the transition be audible?

Not at all. Class A/B has 2 outputs where one side only passes the positive part of the signal and the other for the negative side. You also just doubled the output power. Can you hear the switch over? Um no. Some manufacturers will start in class A then switch to A/B for more power.

Then Class D... some type of switching amp, where it switches on and off? This makes no sense to me either. And why the heck did I think it was a Digital amp?

The outputs are turned on and off very fast (usually in the mega hertz or way out of the audible range) and then filtered. So the output is on as much as it is turned off. But the resulting output like the input is analog (sine wave). Digital is a bunch of square wave pulses that needs to be converted to analog. With Class D the signal is analog with the power being turned on and off.

Of course it gets much more complicated than that but it's my most basic understanding of the different classes of amplification.

Xt explained it pretty well I would say.

THe Wikipedia article is a good one and highlights key advantages and disadvantages of each.

The main advantage of Class D is its efficiency, and often a resulting smaller package. Class D amps are a practical alternative in cases where a large heavy and expensive monster class A or class A/B amp would be needed for best results otherwise due to speaker power and current demands. Its a common case these days that smaller inefficient speakers with extended bass are designed to fit tighter quarters. A Class D amp fits this need well. Some good quality 250 w/ch Class D amps with decent current delivery capabilities can be had for less than $1000 these days. Most smaller ineffficient speakers capable of extended bass in larger rooms will likely benefit sonically from teh extra power and current.

In my case I find the high power Class Ds to be uniquely capable of driving the larger OHM speakers that I like, hence my enthusiasm over that pairing in particular. They also benefit my smaller Dynaudio monitors compared to other higher power SS amps I have used in the past, but the benefits are greatest whenever more power and current out of a smaller more efficient package is what the doctor ordered.

B_Limo, in a lot of cases, the answer is... "It depends"... But here are some specifics as they have applied to class D amp I have used... ROwland M312, Merrill Veritas monos, Belcanto REF100M and REF500M, Rowland M925.

Q: Leave on 24/7?
A: Yes, in all cases... Takes at least 24 hours of playing time for all class D amps in my test set to reach peak performance after being off for a spell.

Q: Plug in its own AC circuit?
A: It depends.... Amps with high degree of power supply isolation like Rowland M925 do not inject much noise back into the AC line, others do. In all cases, you may get slightly better dynamics by plugging power amps in a dedicated outlet.

Q: Stacking or not.... RF leaks?
A: It depends again on degree of isolation... Newer amps like Rowland M925 and Merrill Veritas do not leak RF... Try moving an FM radio on top of them... You will not hear any additional hash on the radio... IMO stacking is OK with these... Both amps are based on Hypex NCore NC1200 modules.

Q: What power cords?
A. Use high current capable power cords... with class D amps, instant current swings/transients can be huge. Do not use analog cords for low power applications, nor old style "digital" cords like the old Shunyata VX.... They will "caramelize" the sound. Note that some cable manufacturers might have today new styles of digital-ready PCs that handle high current class D amps... E.g. Check with the Shunyata factory for their recommendations.

Let me know if you have further questions. G.

One other thing I would note about Class D amps is that they typically seem to have very high damping factors. That will play well with larger speakers taht can benefit with more control of the driver movements as a result of the high damping factor. My large OHm F5s use a 12" walsh style driver known to benefit from high damping in terms of bass control and articulation and that is in fact the result.

Due to high damping, Class D amps can come off as somewhat lean in other speakers. That is the case with my smaller Triangle monitors in particular. I have those set up accordingly to compensate and the results are still quite top notch. My Dynaudio monitors are more in between. I like the clean taut articulate bass that results with them as set up (see my system pics) but I could easily see where some might consider the sound a bit too lean despite the fact that the bas is all there and very detailed and accurate. it just won't be shaking the rafters, at least on most recordings.