Heath IG-18 IG-5218

jackinnj · 16th June 2010, 08:52 PM

Decided that in fairness to the THD, s/n thread the IG-18 should be discussed on its own.

I modified this IG-5218 a long time ago -- looks like it's in need of modding again --

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kevinahcc20 · 16th June 2010, 09:01 PM

Have you looked at the classic "Greening of the IG-18" article by Ed Dell (1971)...I've been picking away at the items but have no distortion analyzer to judge the outcome.

jackinnj · 17th June 2010, 11:25 PM

Disconnecting the Schmitt Trigger:

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Damon Hill · 18th June 2010, 12:29 AM

Just for fun, I once dropped in a TO-5 version LM317 for the power supply's regulator transistor, with appropriate changes and substitutions of parts on the little PCB; works great.

The meter circuit significantly loads the output and benefits from a buffer amp; a precision meter rectifier/buffer from an opamp that mounts right on the meter terminals is one of those projects I never got around to designing...

TheGimp · 21st June 2010, 02:38 PM

I have an IG-18 (1969?) that I just finished doing most of the mods per the Williamson article. I have not done the driver transistor pair yet as I am waiting on parts. I have a pair of 2SC2235/2SA965 on order (ebay) to try.

I also have an HP333A that shows almost identical distortion numbers, so I believe the plots I'm getting with AudioTester V3 thorugh my M-Audio M-192.

I get less distortion (0.008%thd) and higher harmonic/interference with the IG-18 than I do if I use the computer sound card output (M-192). This is at 1Vrms.

A LM317 may be next after the driver transistors.

JimT · 2nd July 2010, 12:39 AM

TheGimp,

Please list your substitutes for the Greening of the IG-18. I am planning on working on my IG-5218 and could use a leg up on the substitutes.

Thanks
Jim

jackinnj · 2nd July 2010, 02:10 PM

The Kruger modification in The Audio Amateur 3/84 is probably the best -- the author ditches the transistor oscillator and substitutes an NE5534. The light bulb AVC is replaced with a photo-dependent resistor AND amplitude compensation is added via a new wafer on the range switch. He also provides for switching the square wave circuitry on or off. As mentioned before, the square wave circuitry adds a lot of noise.

JimT · 2nd July 2010, 05:33 PM

Thanks Jack

I have ordered the 1984 back issues. It should be interesting to compare the three methods of improving the IG-18/5218.

Jim

multisync · 2nd July 2010, 06:07 PM

I did a bunch of mods based on several articles, but I was never able to go below 0.01% ( HP 334A). I mounted the power transformer outside, used +/- 20 volt 317/337 regulators, used a LMEXXXXX 22 volt op amps, for the oscillator and a LME XXX for output, bypassed the output cap, output offset is near 0 volts, used switches to enable square wave and meter, meter is now buffered and with 1000uf across the meter it is basically flat from 1 hz to 110khz slow but flat, used a led for power lamp.

jez · 25th August 2010, 02:58 PM

I made a clone of the ig18 from the audio amateur article. it has all the mods from the article plus some of my own and has given excellent service for many years now.
Distortion is very low. my home made distortion meter has a minimum reading (noise floor) of 0.0016% with the input shorted. It shows the same figure from the "IG18" so it must be considerably better than this figure!

16th June 2010, 08:52 PM	#1
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	Heath IG-18 IG-5218 Decided that in fairness to the THD, s/n thread the IG-18 should be discussed on its own. I modified this IG-5218 a long time ago -- looks like it's in need of modding again -- An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.

16th June 2010, 09:01 PM	#2
kevinahcc20 diyAudio Member Join Date: Apr 2009 Location: Farmington Hills, MI USA	Have you looked at the classic "Greening of the IG-18" article by Ed Dell (1971)...I've been picking away at the items but have no distortion analyzer to judge the outcome. __________________ Kevin(ahcc20)...I'd rather have a bottle in front of me than a frontal lobotomy!

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17th June 2010, 11:25 PM	#3
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	Disconnecting the Schmitt Trigger: An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.

18th June 2010, 12:29 AM	#4
Damon Hill diyAudio Member Join Date: Mar 2001 Location: Auburn, WA (somewhere between Seattle and Tacoma)	Just for fun, I once dropped in a TO-5 version LM317 for the power supply's regulator transistor, with appropriate changes and substitutions of parts on the little PCB; works great. The meter circuit significantly loads the output and benefits from a buffer amp; a precision meter rectifier/buffer from an opamp that mounts right on the meter terminals is one of those projects I never got around to designing...

21st June 2010, 02:38 PM	#5
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	I have an IG-18 (1969?) that I just finished doing most of the mods per the Williamson article. I have not done the driver transistor pair yet as I am waiting on parts. I have a pair of 2SC2235/2SA965 on order (ebay) to try. I also have an HP333A that shows almost identical distortion numbers, so I believe the plots I'm getting with AudioTester V3 thorugh my M-Audio M-192. I get less distortion (0.008%thd) and higher harmonic/interference with the IG-18 than I do if I use the computer sound card output (M-192). This is at 1Vrms. A LM317 may be next after the driver transistors.

2nd July 2010, 12:39 AM	#6
JimT diyAudio Member Join Date: Oct 2004 Location: Waterloo	TheGimp, Please list your substitutes for the Greening of the IG-18. I am planning on working on my IG-5218 and could use a leg up on the substitutes. Thanks Jim

2nd July 2010, 02:10 PM	#7
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	The Kruger modification in The Audio Amateur 3/84 is probably the best -- the author ditches the transistor oscillator and substitutes an NE5534. The light bulb AVC is replaced with a photo-dependent resistor AND amplitude compensation is added via a new wafer on the range switch. He also provides for switching the square wave circuitry on or off. As mentioned before, the square wave circuitry adds a lot of noise.

2nd July 2010, 05:33 PM	#8
JimT diyAudio Member Join Date: Oct 2004 Location: Waterloo	Thanks Jack I have ordered the 1984 back issues. It should be interesting to compare the three methods of improving the IG-18/5218. Jim

2nd July 2010, 06:07 PM	#9
multisync diyAudio Member Join Date: Jan 2008 Location: Carp	I did a bunch of mods based on several articles, but I was never able to go below 0.01% ( HP 334A). I mounted the power transformer outside, used +/- 20 volt 317/337 regulators, used a LMEXXXXX 22 volt op amps, for the oscillator and a LME XXX for output, bypassed the output cap, output offset is near 0 volts, used switches to enable square wave and meter, meter is now buffered and with 1000uf across the meter it is basically flat from 1 hz to 110khz slow but flat, used a led for power lamp.

25th August 2010, 02:58 PM	#10
jez diyAudio Member Join Date: Jan 2004 Location: n.e england	I made a clone of the ig18 from the audio amateur article. it has all the mods from the article plus some of my own and has given excellent service for many years now. Distortion is very low. my home made distortion meter has a minimum reading (noise floor) of 0.0016% with the input shorted. It shows the same figure from the "IG18" so it must be considerably better than this figure!