SV: Re: [sdiy] Why do we need the buffers? - gm-C filter question

[karl dalen]

Some years ago i built a buff less 4pole LP filter
out of a SSM2164, sounded awfully dry and dull, like
mouth filled with cotton! HF response was terrible.
I tweaked a lot but to no awail. Impedance problems
anyone!

KD    

--- "JH." <jhaible at debitel.net> skrev:

> > But the bias current sucked into the next stage would create offsets, 
> > since the direction of this will be always the same, so your filter caps 
> > see a current difference of this error current and shift their voltage.
> 
> Good point.
> 
> 
> > > No, I think the main drawback is parasitic Cs.
> > 
> > Interesting point. Then again why not simply interpose a unity gain 
> > buffer. That should lower the capacitances.
> 
> It's been a long time, but I think I got reduced HF attenuation even
> with buffers, when compared to buffers and amplifying / attenuation.
> 
> JH.
>