[sdiy] Shruthi 4PM (was re something else...)

[David G Dixon]

> I don't have the filter in question so I can't test the 
> actual hardware. 
>   However, a quick circuit simulation will show you how much 
> the stop-band attenuation of the band-pass and high-pass 
> outputs is compromised by innaccurate summing resistances.  
> You could do a Monte Carlo analysis if you really want to 
> know what the worst case mix of tolerances would result in.

In all my filters where I have derived HP and BP from LP, I have always put
a trimmer on the final summing stage to be able to "tune out" stray signal.
It adds a bit of cost and a bit of work, but it solves the problem.