[DESIGN] Original(?) mike-amp design

[bcarso]

Does anyone know what roughly the electrical equivalent circuit of a typical dynamic mike is? It would be interesting to know what portion of the nominal impedance is in fact resistive and hence generating thermal noise. It would also be helpful for judging the importance of parallel ("current") noise at the preamp input.

 

[Samuel Groner]

Bill Whitlock gives some SM-57 data in the chapter on "Preamplifiers and Mixers" of Handbook For Sound Engineers. The impedance above 1 kHz is modelled as 300 ohm plus 6 mH in series. At about 150 Hz there is another peak up to about 550 ohm due to diaphragm resonance.

Samuel

 

[bcarso]

[quote author="Samuel Groner"]Bill Whitlock gives some SM-57 data in the chapter on "Preamplifiers and Mixers" of Handbook For Sound Engineers. The impedance above 1 kHz is modelled as 300 ohm plus 6 mH in series. At about 150 Hz there is another peak up to about 550 ohm due to diaphragm resonance.

Samuel[/quote]

Thanks. That definitely underscores the importance of evaluating the preamp contribution with something more representative than a 250 ohm resistor.

 

[PRR]

> most real world analog sources rarely achieve a S/N greater than 90dB

Huh? I paid $3,999.97 for this 24-bit A/D. For that price, ALL my signals better pop out with 144dB S/N ratio, even if there's a major highway outside the concert hall windows.
--------------------

Yes, I know full well what the acoustic S/N ratio is for most of my recording situations. Often it does not challenge 7.5ips tape.

I must admit that I have not heard mike or preamp noise in a long time. (I do recall some 558+4R PA mike inputs that roared, and a BiAmp that never quite got down to no-noise.)

So my low-noise mutterings were quite pointless, especially since there's no FET in it. Sorry to have wasted everybody's time.