[Audio Empire]

On Wed, 24 Mar 2010 13:24:45 -0700, Ian Bell wrote
(in article ):

Audio Empire wrote:
On Wed, 24 Mar 2010 03:54:59 -0700, Arny Krueger wrote
(in article ) :

"David Nebenzahl" wrote in message
.com

I'd say that since a differential amp practically
eliminates common-mode noise, there's no reason *not* to
use one (which, after all, was the question the OP asked).
Transformers are an effective means of elimination common-mode noise. They
are as a rule more effective than differential amplifiers. If you have an
input transformer, you don't need a differential input and you pick up
some
inherent protection against EMI and casualty losses.

Now that's interesting. My sources all say that transformers have a lower
common-mode rejection ratio than can differential amplifiers.


'Have' and 'can (have)' are not identical conditions.

Cheers

Ian

snip

Well, of course, we're comparing best-case scenarios here. A transformer is a
transformer, and while there are a number of makers of microphone
transformers, they are all very similar in design and all have transformer
characteristics in the same proportion, both good and bad. Differential
amplifiers, OTOH, come in a myriad of configurations from cheap 709 style
op-amps to very good ones like the latest National Semiconductor LM 497XX
series to differential amps made with selected discrete components to potted
gain modules made specifically for the pro recording industry. A transformer
can be better than a old-school 709 or 741 era op-amp, but newer op-amps are
much better than that wrt common mode rejection ratios.