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-   -   Heath IG-18 converted to state-variable design (http://www.diyaudio.com/forums/equipment-tools/174949-heath-ig-18-converted-state-variable-design.html)

richiem 7th October 2010 07:50 AM

Heath IG-18 converted to state-variable design
 
Hi folks -- I just received a replacement for my dead digicam, so I took some pix of my project to convert an IG-18 to Bob Cordell's state-variable oscillator design. Performance is very good, bordering on great. Here's the URL:

IG-18 #2

Best,
Dick Moore

Ernie Milko 7th October 2010 05:00 PM

Nice work, Mr. Moore.
I love my IG18, and a path like this is something I've been considering for some time.

richiem 7th October 2010 07:49 PM

Thx, Ernie -- another path I'll look at sometime relatively soon is increasing the capacitor ratio in the Bridged-T in the IG-18. It's 10:1 stock, but I think a few easy changes could let it be higher, say 34:1, which would raise the filter Q significantly and steepen the slope of the phase change through zero degrees, which should lower distortion and increase stability. HP uses a ratio of 100:1 in the 239A/339A, but the IG-18's amplifier won't go that far without serious mods.

richiem 15th June 2012 08:09 AM

I've updated the web page on the Cordell SV oscillator built into the IG-18 -- added some high-resolution spectra of the distortion performance -- it is just excellent. See the page:
IG-18 #2, the BIG-18


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