Paul B. wrote:

>> halved because the input impedances of the amps are now in parallel.
>> This is a faulty analysis, though, and would only be true if the input
>> impedance of the amplifier was comparable to the source impedance of
>> the transducer.  In fact, the amplifier impedance can be _much_ higher
>> than the transducer impedance.
>
>  REALLY? Well, in that case, wouldn't it be far more sensible to match
>the impedance better by using a step-UP transformer before resorting to
>parallel amplifiers?
>
>  Hint:  That's how they do it in microphone pre-amplifiers.  They do
>however not infrequently trade off poorer noise figure for lower cost
>and/ or slightly flatter frequency response by omitting the transformer
>and using a second pre-amp module to provide a balanced input.  This is
>however, just that, a trade-off.
>

I defy you to come up with a transformer (or any magnetics, for that
matter) that has anything approaching within several orders of magnitude a
2000 ohm to 10**12 ohm impedance difference.

Besides, I'd say the impedance mismatch is the reason why the amplifier is
useful--it doesn't load the transducer significantly. The object is not to
maximize power transfer from the transducer to the amp, but to amplify the
signal.

--BN

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