Heath IG-18 converted to state-variable design

richiem · 7th October 2010, 06:50 AM

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, 04:00 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, 06:49 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.

7th October 2010, 06:50 AM	#1
richiem diyAudio Member Join Date: Sep 2010 Location: Grapeview, WA	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

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7th October 2010, 04:00 PM	#2
Ernie Milko diyAudio Member Join Date: Sep 2010	Nice work, Mr. Moore. I love my IG18, and a path like this is something I've been considering for some time.

7th October 2010, 06:49 PM	#3
richiem diyAudio Member Join Date: Sep 2010 Location: Grapeview, WA	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.

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