Bruno Putzeys on Class D amps for cutting:
"I get this question mailed directly to me by cutting engineers with surprising regularity. I'll leave aside the usual diatribe about the verifiable nonexistence of something like a digital amplifier (it's at http://www.hypex.nl/docs/allamps%20hypex%20layout.pdf if anyone's interested).
The important question is: what are the advantages to using class D?
Those are the *only* defining characteristics which cannot be emulated or obtained more easily using non-switching power stages. In all other aspects, class D is a decided burden. Characteristics which are possible, but very difficult to achieve in class D are:
*Low distortion, low output impedance, uncoloured sound etc. Some makes of class D amps have a reputation for good sonic and measured quality. This is not because of class D but in spite of it. It's really hard.
*Absense of a switching residual. A small amount of residual is of no consequence in a loudspeaker, but would you like to cut a 400kHz signal, even a very tiny one, into a groove? I think not.
Characteristics of linear power amps that are impossible to get with switching power stages are:
*Simplicity of design
*Very wide bandwidth
And in the context of cutting
*Very high output impedance
*Ease with which a supplementary feedback loop is added
To make a long story short. Efficient is nice when a million people have their stereos on. Compact is nice when the product goes into your living room. Neither are particularly important when you're cutting records. Each record is cut exactly once, so the heat output is lost only once. And 4u of rack space next to the lathe isn't going to spoil an already geeky interior.
What you do need is:
*A feedback loop from the sense coils, preferably one that doesn't take a seasoned control theoretician two years to work out. A wideband amplifier makes this almost simple.
*Current out (one could work around that).
A class D amp to drive a cutting head solves nothing and only adds more problems."