Climbing the Moog ladder

[BJ]

Tony Allgood wrote:
> 
> Well in my search for the perfect filter, I've given up on the noisy
> 13700, I had to try the famous Moog ladder. Well I've built it before,
> but I thought I would try to improve on it. I used a stereo pot for the
> Q ( Emphasis!! ), one of the gangs controlled the feedback as in the
> original design and the other gang controlled the input level to the
> filter. The input levels are dropped to about 25% at low Q settings to
> compensate for the drop in output at higher Q settings. Using 10k log
> pot and 3k3 resistor, this works really well. The output level stays
> pretty much constant over the pot's travels. I used the 10k pot in
> potential divider mode in the feedback path. I think this gives a
> better law than the traditional 47k/50k pot in variable resistor mode.
> Plus I can't get miniature pots at 47k in stereo anyway.

> 
> Cumbria, UK
> 
> 'I may live in the middle of nowhere, but the views are nice'

Why do you say that the LM13600/13700 are noisy,I have done lots of
different 
OTA filters with it for many years now, and mine are wery quiet indeed!
On the other hand the "Mogo laddero" filter are wery sensitive to the
use of components
since it is a differential filter design and therfore more noisier then
the OTA filter!
And now i put on the flames dress! :-)

BJ
PS:I don't match the ladder transistors,but i do use low noise
transistors.
If people can use the 3080 in a filter design over and over again,
i can't see any problem using a LM13600.