[sdiy] Resistor War !!!

[Paul Schreiber]

> So how can two different resistors of the same value produce different
noise
> figures? Are we talking about mechanical noise sources such as
microphonics
> or vibration sensitivity?
>
> Otherwise that does not make any sense. Resistors are not active voltage
> sources, so how can one type produce more noise than another? (since they
> don't actually generate additional noise at all?)

HA!

This was a favorite "HP Interview" question from the '70s (HP was infamous
for 6-hour technical interviews!)

Q: How can you measure the value of a resistor *without* passing ANY current
through it?

A: Measure the RMS *noise* amplitude at 2 different temperatures.

Yes, a resistor "just sitting there" has thermal noise. In fact, in mic
preamps you had *better* watch to see
resistors are <say 800 ohms, or their thermal noise swamps the mic preamp.
Jim Williams of Linear Technolgy
wrote a great article on this, and also check Bob Pease's book
"Troubleshooting Analog Circuits" which
is equivalent to a 2-year tech school degree for $30.

Paul Schreiber
Synthesis Technology

www.synthtech.com <<MOTM analog modulars