Class A overdrive -- definition

[amptramp]

"Class A" means that the output device or devices, it doesn't matter how many, operate throughout the entire signal swing.

But the reality is this: If it is a circuit in a pedal running off of 9V, it's almost guarenteed to be class A. Class A is the cleanest, the least sensitive to bias arrangements and normally has less parts to possibly fail. The only reason to move out of class A is to limit power dissipation in the output devices. And at 9V and a couple of milliamps, dissipation is rarely a concern.

In my opinion, the prime example of a "Class A Overdrive" would be the Rangemaster.

Regards,

Jay Doyle

I am not entirely sure of this.  Some op amps run class AB and run off 9 volts.  Some audiophiles recommend biasing an op amp with an output resistor to the negative supply to achieve Class A.  But then that would assume that it matters more than it actually does.  But I would agree with most people that this is of no consequence unless you are looking for 0.01% THD.  Certainly not a factor in a distortion pedal.

[jafo]

It's worth noting that you can get extremely low distortion figures from push-pull, perhaps even easier than with Class A. It's just a different flavor of distortion, one weak(er) in (often even lacking), even-order harmonics. If you want fidelity and efficiency, push-pull is probably your best bet. Op amps use it.

If you want to hear distortion and your ears like even-order harmonics (mine do!), Class A is worth considering, but most people can't tell the difference, and many people prefer a distorted push-pull -- it's basically the difference between a cello (a sawtooth wave, with even and odd harmonics) and a saxophone (which is mostly odd).

Again, it's just a difference in character, which comes down to taste. (But push-pull is much more efficient in terms of power). It's really not a big deal, especially when compared to something interesting like how different devices transition between clean and distorted.

[ORK]

Class A power amps don`t suffer from sag. If you would call it suffer.

[BubbaFet]

"Class A" means that the output device or devices, it doesn't matter how many, operate throughout the entire signal swing.

But the reality is this: If it is a circuit in a pedal running off of 9V, it's almost guarenteed to be class A. Class A is the cleanest, the least sensitive to bias arrangements and normally has less parts to possibly fail. The only reason to move out of class A is to limit power dissipation in the output devices. And at 9V and a couple of milliamps, dissipation is rarely a concern.

In my opinion, the prime example of a "Class A Overdrive" would be the Rangemaster.

Regards,

Jay Doyle

Hey! That was the mysterious JDoyle! The man... the myth... the legend.....
I'm a fanboy.

[boogietone]

And what are the benefits of a class A type of overdrive as opposed to other types, especially in pedal design?

Solely that it looks cool in advertising copy to people who don't know what it means.

It's a little like

"DANGER!! 50,000 OHMS!"

Now, that is funny!