[sdiy] RE: [AH] Parametric EQ

[Neil Johnson]

Hi,

Tom Wiltshire wrote:
>> The solution I used in my 3-pole filter is to configure the zeners  
>> as the bottom leg of a potential divider from the output of the LP  
>> integrator back to the input.  See here:
>>
>> http://www.milton.arachsys.com/nj71/pdf/cesyg/vcf-sch.pdf
>>
>> In this case focus on IC3A, with R10 and D1,D2 form the potential  
>> divider.  This keeps the main signal current path clean.
>
>
> Interesting. Does this provide an audible improvement over putting  
> the zeners across the op-amp, Neil? It sounds like it ought to, but  
> do you hear it in practice?

A couple of things:
- greater stability in self-resonance
- wider frequency response down to a few Hz.

> Presumably this DC current path in parallel with C4 will make the  
> integrator into a slightly leaky integrator?

Yes, in your case.

> What's the effect of having a small current drain to ground instead?

 From where?  The -ve input to the op-amp?  If so, then a DC offset  
to the input, causing the integrator to saturate.

Cheers,
Neil
--
http://www.njohnson.co.uk