[sdiy] VCA signal analysis

[Neil Johnson]

Hi,

cheater00 wrote:
> [HP8903B]...and with 70 dB dynamic range perfect for testing the fidelity of
> transatlantic phone lines :-)

A rough hand-wavey estimate: at the top end the maximum input is 300V,
at the bottom end the residual noise and distortion (20Hz - 20kHz,
80kHz BW) is 15uV (all datasheet numbers - I haven't had mine
calibrated yet so I can't give you cal.cert numbers), giving a dynamic
range of about 146dB.

For my purposes (messing around with old mixers and old analogue
synths, and designing synth modules) it's good enough.  If you want
more than that then you really need to step up to an AP.  I think Paul
Schreiber has (or had) one.

A notch filter also allows you to spend your limited sensitivity and
resolution on exploring distortion artefacts.  You can pump a healthy
signal into your circuit (VCA, filter, telephone line, etc), notch out
the fundamental, and then turn the gain up so you can see the all the
annoying harmonics from the distortion mechanisms in the circuit.

Neil
--
http://www.njohnson.co.uk