[Jim Gregory]

"Edward Morris" wrote in message
.. .
Hello,
I have a C22 preamp and it has RCA shorting plugs in the Phono 2
inputs,
the Tuner 2 inputs, the tape head inputs and the MIC inputs. Are these
shorting plugs necessary and should they be used in all unused RCA inputs
jacks?

Thanks for your help,
Edward


Such shunt plugs are inserted only when needing to -measure- noise
self-generated from a particular pre-amp stage, especially mics.

A v good Mic hum + noise figure would be 62dB lower than a usual active ref
programme level of 1mW at pro' line output. Possibly a lower o/p level on
domestic circuits. Not sure about the datum found in a McIntosh design.

But noise figures in gram PU and tape-head circuits are sloped, frequency-
dependent because of frigged equalisation curves in the AF band either side
of 1kHz.
When evaluating a stage's quality, the shunt resistor should not be zero
Ohms but ought to mimic the source impedance of the -relevant- transducer.
I.e., 'dynamic' mic evaluator should be a 150r to 200r low-noise MO
resistor - to simulate a muted! mic.
Jim