[sdiy] Leapfrog (was: Re: Cauer Filter Design)

[jhaible]

> >I still hesitate to build a circuit where the signal would run
> >thru
> >50 or even 75 opamps. Not sure how the ever so tiny unwanted side effects
> >of an opamp will add up in a long signal chain. For *that* application, I
> >guess
> >it's easier to just use 25 cheap inductors.
>
> It's my understanding that the version with the inductors requires a fair
> amount of "post amplification", is that correct?

No. A few dB's - that's all.
Of course in a Hammond, the couling is capacitive over the Scanner, which
needs
an aplifier with capacitive feedback, and in my version, signal is divided
down
to 10mV for a differential pair as VCA
(see
http://www.oldcrows.net/~jhaible/scanner_vibrato/jh_scanner_vibrato.html)
so there is always some extra amplification needed, but that's not because
of the
LC line box.


> Does the version using
> opamps avoid the massive signal loss of the inductor-based approach? If
so,
> there might be some merit in the opamp approach after all. It might help
> preserve the S/N ratio better than the inductor approach.

No. The only problem with the LC circuit is size, and the need of shielding
against hum.


> If you ever finish the design of the opamp version, please let me know. I
> think I want to try building it! Remember, the most "sane" projects aren't
> always the most interesting or fun projects.  ;)

I won't build this anytime soon (the GIC String Filter Bank is first,
and then probably the dual/stereo Frequency Shifter). But I have
made a drawing of a shorter circuit (8 stages) to show the idea.
I will post this sooner. But it's untested.

JH.