[sdiy] Leapfrog

[Magnus Danielson]

From: Glen <mclilith at charter.net>
Subject: Re: [sdiy] Leapfrog (was: Re: Cauer Filter Design)
Date: Tue, 06 Jan 2004 15:35:32 -0500
Message-ID: <4.1.20040106151944.024e5a80 at mail.charter.net>

> At 02:09 PM 1/6/04 , jhaible wrote:
> 
> >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? 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. 

You can get fairly good loss numbers out of an LC chain, so that should not be
a problem. The commutator is under suspission from my side.

> It should also be much more immune to magnetic interference, compared to
> the inductor version, and might be less susceptible to hum pickup. 

Yeap. Also, you don't have to consider the coupling between the inductors.

> If built with surface-mounted quad opamps, I wonder how large the circuit
> would actually be? It actually fit on a reasonably sized circuit board.

SMD quad-opamps and SMD resistors makes this thing fairly small if your in the
mood for SMD. The complexity of the design remains the same otherwise (SMD can
reduce complexity of a design by the reduction of mechanics, contacts, cables,
even if the amount of components doesn't change, so it's true in a system
sense).

> Would the op-amp version of the filter be more accurate? What are the
> tolerances of the inductors you used, versus the tolerances of the
> components that would be used in an opamp version?

I think there's a benefit for the op-amp case here.

> 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.  ;)

Indeed. Indeed.

For myself I have toyed with the idea of doing the commutator in solid-state.

Cheers,
Magnus