[sdiy] Simple discrete Unity-Gain Follower ?

[Grant Richter]

> Is it possible at all to make a transistor unity-gain buffer without
> feedback? Somehow you have to get the gain down to 1.
> 
> An emitter follower sure does have feedback. The voltage drop across
> the emitter resistor is in series with the input voltage.

Bear in mind that feedback is one of the wonders of the modern age. The
application of negative feedback to op-amp circuitry solved a huge number of
problems.

Mainly the gain of an open loop stage is temperature dependent in the
extreme, and devices with gain have parameters that can vary by 300% (like
transistor beta) in the manufacturing process. So unless you like to do a
lot of incoming inspection and sorting, feedback is your friend.

What I think your talking about, is how to prevent the feedback loop from
FAILING. That is when it makes things worse, rather than better.

To reassure yourself that feedback is working, just measure the voltage
differential between the + and - terminals of an op-amp. If negative
feedback is working, there will be no difference. If it fails, there will be
a differential signal. You can then eliminate the differential signal and
"fix" the feedback loop.

Most of the "audiophile" distaste for feedback loops refers to the failure
of the feedback loop, not when it's working properly.