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Subject: Re: Historical question: negative feedback and the op amp
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Fri, 15 Nov 2002 09:38:41 GMT
NNTP-Posting-Date: Fri, 15 Nov 2002 10:38:41 MET
"Chuck Simmons" schrieb im Newsbeitrag
> This part of the thread was inspired by ideas set forth that negative
> feedback in particular can somehow be replaced by digital systems of
> arbitray precision and speed. In other words, the idea of the
> operational amplifier is dead or soon will be.
you expressed exactly what I wanted to say.
Kevin brought up the application of an audio amp. Here latency doesn't
disturb at all, so all kinds of filters can be used.
It is also not much different from a normal control, just that all 16 or
24bit output states have to be reproduced continuously. There is the amp and
But now the feedback signal is taken from the output voltage! Also it should
be possible to connect all different kinds of motors with the amp staying
And when measurements are taken, instead of the motor a fixed resistor is
connected and now the amp produces 0.001% distortion and has an output
impedance of 0.01 ohm.
These measurements are absolutely irrelevant. The feedback signal is a sum
of the counter voltage and output voltage.
And look at the motor, or lets say 3 motors in a box. They have a crossover
with 4th order filters, what can be said more.
And when you measure the distortion of the original signal with 3 generators
at different (fixed) frequencies connected to the output as well, that would
be more appropriate. I do not want to see the result...
Now analog this couldn't be done, but digitally we have the chance to
calibrate the whole system with 2 mikes in the ear channel or whatever.
We can even shoot a few times to create a pulse response of the room and
mike, so the "feedback" is conserved, because it will be always similar and
with the reverse filter many deficiencies can be already eliminated. With
more DSP power even unlinearities at higher levels can be compensated for.
Now sit in front of your expensive stereo system and put a good classical
chamber music record. Why doesn't it sound like "live". Why can you exactly
point to each loudspeaker and have problems to locate the virtual location
of the sound sources?
This is where I'm working at since a couple of years and when you visit me
and listen to my sound system you will be surprised!
electronic hardware designer
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