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Old 26th December 2003, 01:29 PM   #1
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Question Is distortion random ?

Hi,

are K2, K3, .... Kn in phase or out of phase (random phase angle) when produced by two identical amps which are fed with same sine signal.

If identical amps are paralleled, will distortions become smaller ?


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Old 26th December 2003, 02:06 PM   #2
Bricolo is offline Bricolo  France
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No, I don't think so. But I'm not 100% sure.

Noise is random
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Old 26th December 2003, 02:22 PM   #3
sreten is offline sreten  United Kingdom
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Distortion is not remotely random, noise is entirely random.
Induced noise, e.g. hum, ripple, crosstalk is not random.

THD is the sum of noise and distortion.

If amps are paralleled, theoretically thermal noise is reduced.
Output stage distortion is usually related to output current,
and paralleling amplifiers will reduce output stage distortion.

sreten.
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Old 26th December 2003, 02:30 PM   #4
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Thanx,

so will only parallel amps reduce distortion or also paralleling output devices

Are separate feedback loops necessary ?

I read that some bridge configurations will lead to distortion cancellations of even or odd orders (only). Why ?

Besides parallel DAC chips, I wonder if it is possible to synchronize sine generators as ICL8038 or stuff like that, to reduce distortion.

And op amps...


Bernhard
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Old 26th December 2003, 02:59 PM   #5
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If you have two identical, non-linear amps which have a symmetrical non-linearity, you can feed signal S into one and signal -S into the other and subtract the outputs to cancel the distortion.

If the non-linearity is not symmetrical it doesn't work.
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Old 26th December 2003, 03:08 PM   #6
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Quote:
Originally posted by traderbam

If the non-linearity is not symmetrical it doesn't work.
And how do I know if it is sym ?
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Old 26th December 2003, 03:26 PM   #7
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That's an interesting question!

I don't know.
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Old 26th December 2003, 08:16 PM   #8
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by traderbam
If you have two identical, non-linear amps which have a symmetrical non-linearity, you can feed signal S into one and signal -S into the other and subtract the outputs to cancel the distortion.

If the non-linearity is not symmetrical it doesn't work.

Erm.... I think you've got this the wrong way round.
Balanced topologies cancel asymmetric distortion but
cannot cancel symmetric distortion.

By using a balanced configuration the asymmetric distortion
is the opposite in the other channel, so they are symmetric in
this sense, which is why they cancel.

Even order distortion is assymetric, odd order distortion symmetric.

sreten.
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Old 26th December 2003, 08:59 PM   #9
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Default Re: Is distortion random ?

Quote:
Originally posted by Bernhard
Hi,

are K2, K3, .... Kn in phase or out of phase (random phase angle) when produced by two identical amps which are fed with same sine signal.
if you feed identical signals to identical amps, the output should be identical, short of any randomness in the process (like noise).

I tend to think distortion (as induced by component or design) isn't random. For example, running an A/C signal through a diode should always yield you a half wave, which in itself is distortion.
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Old 26th December 2003, 11:15 PM   #10
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Quote:
Originally posted by traderbam
If you have two identical, non-linear amps which have a symmetrical non-linearity, you can feed signal S into one and signal -S into the other and subtract the outputs to cancel the distortion. If the non-linearity is not symmetrical it doesn't work.
That is not literally true. For example, you cannot make
intermodulation go away in a like fashion.
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