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Class D is just Dandy!

I thought it was time we had a pro- Class D thread. There's plenty of threads about comparisons, or detractors of Class D.

That's fine, you don't have to like Class D amps, and if you don't please go participate on one of those threads.

For those of us who are very happy and excited about having musical, capable amps that we can afford to keep on 24/7 and don't require large spaces to put them in, this thread is for you.

Please share your experiences with class D amps!
erik_squires
seanheis1
595 posts
 
Linear amplifier distortion can be reduced by feedback, something digital amps may use in buckets.
Using feedback to reduce distortion isn't a free lunch though, or is it? 
erik_squires OP
15,990 posts
 
It may not be, but it works totally differently.

In a digital amp the feedback affects the width of the "on" period.

First, I’m not sure that anyone has proven in a linear amplifier why moderate feedback is a bad thing. Second, in class D it is a couple of stages away from the output signal, so whatever arguments you might have made for a linear amp’s feedback I don’t know that they would work at all.

As I understand it, Technics is using more of a feed-forward loop. They analyze the errors with the output stage, and then digitally correct it ahead of time, before the actual power amplifier stage. Talk about a huge amount of processing and signal meddling though. :)

The Technics approach is VERY similar to digital EQ and phase correction if you were to limit the correction to purely electrical, it is identical in theory.

If you go that far, might as well include the acoustic output of the speakers as well and finish the job. :)



Best,

E
georgehifi's avatar
georgehifi
10,312 posts
 
Using feedback to reduce distortion isn't a free lunch though, or is it?
From what is understood for years by the guru's of amp design, is that any amp should be designed for as little distortion, low output impedance ect., as possible without the use of feedback. Then to use just a little feedback if necessary to clean it up if need be.

Cheers George 
georgehifi's avatar
georgehifi
10,312 posts
 
feed-forward loop
Feed forward was used in the old days, and it was resurrected again by Rogue in their M120 and I believe in their M150/180's.

Cheers George 
erik_squires OP
15,990 posts
 
Hi George,

Feed forward in a linear amplifier is very different. :)

In this case, I’m using it more as an analogy or principle rather than a specific circuit design.

While most amplifiers have feedback at the output stage, the Technics does the correction mathematically at the input, pushing the error compensation from the front instead of the back.

For this reason, I think of this as a feed-forward idea, being the opposite of feed-backwards.

Best,

E
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