On Fri, 13 May 2016 13:08:54 +0100, Mr Macaw wrote:

On Fri, 13 May 2016 11:29:21 +0100, Wayne Chirnside
wrote:

On Sun, 08 May 2016 00:47:57 +0100, Mr Macaw wrote:

I know what a servo motor is, and that you can get servo amplifiers
(or servo drives) to work with them, but what does it mean when a
stereo system says it has a servo amplifier?

There is active circuitry to keep the bias at a point where the output
tracks symmetrically between positive and negative voltage excursions.

I see. Is this to prevent unnecessary DC current through the speaker
creating heat in the coil? Or does it improve sound quality by leaving
the cone centred so it doesn't hit the ends of its movement?

Prevents DC current as well as eliminates the need for capacitors which
always introduce phase shift that annoys purists.

It also eliminates drift but getting the design just right AND fail safe
requires exceptionally careful and thoughtful design.

Very few got it right but when they did it was terrific.
Very few tried because blowing out customers speakers makes for bad
business, all too easy with that design.

Now the new gainclones take all the perfect design out and make it dead
easy to employ DC servo circuitry and all the paralleled chips designs
incorporate this in the design.

However...
They also introduce their own circuit protection and thermal shutdown
that can very easily color and prevent perfect reproduction of loud
transients.

The only way around that is three or four chips servo slaved together
such that they have such an overabundance of headroom they never come
close to the limiting circuitry.

Planning my own gainclone based on the TDA7293 right now AAMOF.
As well as ordering another cheap Chinese digital amplifier having had
the best of luck with the last.
But only after adding my own DC protection circuit should a failure occur.
Quad matched Technics speakers with 12 inch woofers are not to risk!

Believe it or not they sound just great running at 2 ohms off a 25 dollar
Parts Express Lepai digital amplifier up to about 1/2 volume, after that
it's all down hill but for a small room being digital it's more than I
ever need.
YMMV as I've heard the quality of these amps isn't exactly uniform but
mines been running two years w/o an issue.