Arp filters. Re: [sdiy] WP LM3900 VCF

[Aaron Lanterman]

On Wed, 29 Mar 2006, anthony wrote:

> In the meantime I have been looking at the Arp filter schematics. I have 
> several pdf's and even a patent. I really like the design, but it looks 
> like a lot of transistor matching would be involved. I guess you'd 
> really only need matched pairs?

That patent is interesting since the Norton amps have a cap in the 
feedback loop, which a lot of the op amp ap notes tell you _not_ to do... 
:)

You really only need to match the transistors in each pair - one of the 
Japanese duals should work fine I'm guessing, or you could hand match.

If there's mismatch between sections, the poles won't all line up at 
exactly the same spot at zero resonance, but that's not a big deal I 
think.

- Aaron

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