k 2496
Klas, you wrote:
>Note that unless you are going to run microphones with output
>transformers, you don't need to use matched 1% resistors.
Yes, it would perhaps be OK to use less precise resistors. However, a good
match would also preserve a proper balance of the two input rails of the
differential microphone preamplifier. Unmatched resistors would degrade the
"common mode" rejection capabilities of the recorder. This means that
external noise interference would be canceled out less effectively.
This kind of balance should also be preserved within the microphone or in a
dummy microphone circuit for noise test purposes. So, a test circuit that
employs an unbalanced connection scheme might produce worse results than a
balanced microphone. Noise originating from the phantom power circuit is
usually a common mode signal that can be reduced by the balanced
preamplifier input.
Klas, this is the reason why I would not over-estimate the bad results you
got in your test on the MT2496 phantom power. At least the phantom power of
my own MT2496 is sufficiently clean for operating my phantom-powered (and
balanced) K6P/ME66 microphone.
Raimund
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