Re: Is this a good way to test pre-amp hiss of a digital recorder?

"Mike Rivers" <mrivers@xxxxxxxxxxx> wrote in message
news:1149604692.314351.276570@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

I'm not saying that it can't be done, just that it isn't as common as
you seem to think it is. Some people want to try to duplicate
measurements at home, or make measurements that the manufacturer or a
review doesn't provide. For those people, (who are as likely as not to
use an open input) a shorted input is probably better than using a
resistor. They'll get a number that's closer to what's advertised, and
then you can tell them that in the real world, they can expect it to be
about 6 dB worse because it's being used with a real microphone.

No, you can't. It might be the same, it might be 3dB worse, it might be 6dB
worse. Given the short-circuit numbers, AND the knowledge of how the box is
designed (bipolar, FET or tubes), AND information about the current noise of
the input stage (if it's bipolar), you can predict how much worse it will be
with a resistor or microphone. But without ALL of that information, you
cannot make the prediction.

Lab tests should be fully documented, but informal tests should be easy
to understand and compare results.

Yep. Buy a 150 ohm metal film resistor. Solder it into an XLR connector.
Plug it into the input. Measure noise at output (preferably with a 20kHz
bandwidth). Subtract preamp gain and you've got your equivalent input noise.

Peace,
Paul


.

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