Re: Distortion in amplifiers.



John Byrns wrote:

In article <46030633.0@entanet>, Ian Bell <ruffrecords@xxxxxxxxxxx>
wrote:

John Byrns wrote:



What is R6 doing in there? Patrick has already made it clear that
adding a series resistor in the input circuit is cheating and is not
allowed.



How can that possibly be called cheating?

The reason Patrick gives is that R6 greatly increases the negative
feedback in the circuit and his original premise was that the BJT
circuit couldn't use negative feedback. Patrick has posted on this
issue several times already.


Let's clear the air; I didn't definately say adding NFB is cheating at
this
time.

What i have been saying is that without NFB of any kind whatsoever,
the BJT is not a good linear voltage amplifier, ie, with grounded
emitter,
and very low Z linear voltage signal applied to its base so that
the non linear input base resistance does not have any effect on the
base input signal VOLTAGE linearity.

And I have said that collector output VOLTAGE will be distorted.

NFB prevents the naked truth about BJT voltage linearity from being
seen, so its action in any way
must be prevented when testing the raw natural VOLTAGE linearity
transfer funsction between base and collector.

BJTs have a fairly linear relationship betaeen base input CURRENT and
collector CURRENT.

Basic distinctions MUST be made about what exactly are VOLTAGES and
CURRENTS.

In the case of the BJT, if the base input voltage is linear, the current
input will NOT
be linear, and nor will be the current output, and when this current
flows in RL, you see a non linear
output voltage as a result. The RL is a constant linear value of
resistance,
and the dynamic base input resistance and collector resistances are not
linear.

Tube dynamic anode resistance isn't a linear resistance either.

Patrick Turner.



Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/
.

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