Impedance matching for DYI RCA attenutators

[Pharos]

Rothwell must be considering the series resistor as a part of the source impedance as far as the load is concerned.

This is a valid conception in some situations, for example with a loudspeaker where the series resistor would worsen the damping factor, but that is not an issue in purely resisitive signal circuits.

Versed in Thevenin and Norton equivalent cct. calculations, and Pi and L attenuators years ago at Wood Norton, this is all second nature.

[alexk0il]

Rothwell must be considering the series resistor as a part of the source impedance as far as the load is concerned.

This is a valid conception in some situations, for example with a loudspeaker where the series resistor would worsen the damping factor, but that is not an issue in purely resisitive signal circuits.

Versed in Thevenin and Norton equivalent cct. calculations, and Pi and L attenuators years ago at Wood Norton, this is all second nature.

See your point, however my intuition tells me that having a shunt resistor might help to reduce the input noise on the amp inputs.

I would expect the amp impedance to be a function of frequency, temperature, current or god know what else. A slight change in amp impedance will proportionally change the attenuation of your single resistor pad, hence you will get the noise coming in. If instead, as an example, you have an an L-pad with a 1000 Ohm shunt resistor in parallel to 10K amp, then the influence of the amp impedance fluctuations is reduced by the factor of 10.

Or did I get this wrong?