[sdiy] improved dynamic range diffpair-vca

[JH.]

>It really differs what you define as noise in this case. If you only 
>consider
>white noise, pink noise (i.e. random sources) etc. then you are certainly
>correct. Another form is "anything but". This includes hum and its 
>overtones,
>harmonic and non-harmonic distorsion etc. In this form noise is all 
>unwanted
>signal. This form is usefull for actual dynamics.

That's all nice and well, and I can certainly ruin the best Blackmer VCA by 
adding a ground loop and placing it near a transformer. But that's hardly 
the question when we're talking about SNR improovement of one topology 
compared to another. What I want to know: Is my 3dB calculation basically 
right (asuming the diode connected transistors contribute about the same 
amount of noise as the other transistors), or does the circuit really have 
the potential to give 6dB SNR improovement (Because, for instance, the 
diodes contribute less noise than the other transistors) ?

JH.