Old Heathkit IG-18 Sine - Square Audio Generator does a good job!

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rock soderstrom

Tour de France
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I recently found a HAMEG HM 203-6 on a scrap yard, which surprisingly still works perfectly. After a short honeymoon, I have to say that it takes my little "workshop" to a whole new level. I'm glad to have an analog scope again.

As a signal source for the oscilloscope I have my PC, mobile phone and a horrible China 5$ function generator. None of these are really any fun, so I've been looking around for something more suitable.

HAMEG has produced some interesting devices in this area, but unfortunately they are still quite expensive, large and offer a lot of functions that I probably wouldn't need anyway.

So I looked around on ebay, at first I wanted to buy a tube audio generator because the optical design was soooo nice.:love: Unfortunately I was outbid.

Then I blindly bid on a more modern device and actually won - a Heathkit IG-18 Sine - Square Audio Generator for just around 16€ plus 5€ shipping sounded like a good deal.

1000032879.jpg

Yesterday the device arrived, quite dirty, one adhesive foot missing, some battle scars but otherwise in good condition.

The device has been used and also slightly modified - a predecessor has built in a switchable 2W amplifier to (probably) drive speakers directly. Nice.


Further tests showed that everything was in order, this generator plays perfectly, all values are correct, it's really fun!

Here is one (of the numerous) videos on youtube which explains the device in great detail.





To summarize, I have to say, a top purchase, the IG-18 fits perfectly into my cheapskate setup, that's exactly what I need at the moment.
It's a great source for test signals for checking amp circuits, microphones and quickly measuring transformers.

I like the handling very much, the thing pumps out up to 30V peak-peak as a sine wave. The signal quality is very high for my purposes. I might integrate some more mods, the WWW is full of them.

The first thing I ordered was a Banana-BNC adapter. I might add a 200R position to the internal, switchable 600R termination, we'll see if that makes sense.

I am happy 🥳
 
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I have one and despite doing a lot of the mods, I still can't get the distortion lower than 0.089%.
But hey, I don't really need it much better than that for the things I do. 😄
 
I think I had one of those back in the day. IIRC there were several DIY modifications published to reduce distortion and the like.
Yep, right, there are plenty of mods on the internet for this. The device/kit has also been modified by the manufacturer over the years. Some improvements have been adopted.

Here are a few links:

http://www.heathkit.nu/heathkit_nu_IG-18.html
http://www.tronola.com/moorepage/IG-18-1.html
https://www.angelfire.com/electronic/funwithtubes/IG-18_Mod.html

But hey, I don't really need it much better than that for the things I do. 😄
Ha ha, that actually applies to me too. Most of the things I want to do with this generator, are already possible without restrictions. The thing is very practical...
 
I have one and despite doing a lot of the mods, I still can't get the distortion lower than 0.089%.
But hey, I don't really need it much better than that for the things I do. 😄
When I designed the sine wave generator inside the Loftech TS-1 I compromised on around 0.2% THD+N****. I could have made the distortion lower but that would have dramatically increased the settling time. Since I was controlling a 1000:1 frequency range with a single knob, with simultaneous level readout which did not incline customers to be patient.

JR

**** in close either/or listening tests I could hear the 0.2% distortion on LF sine waves where the distortion components were in the midrange, but 0.2% was clean enough for general troubleshooting.
 
FWIW, I have a Leader LAG-120B. 10HZ to 1Mhz, .03%thd. I've had it for 40 years and it works perfectly. I have a reverse RIAA network in it for testing phono preamps and put in RCA jacks for the output for convenience. I think you can find them used fairly cheap, certainly cheaper than a digital one.

Anyone know of a cheap audio sweep generator?
 
Decided to have another tinker with mine and add the constant current mod for Q3 collector.
The distortion is now 0.016% at 1k, 0.023% at 10k, 0.018 at 20k and 0.025 at 100Hz.
These are all unweighted mesurements using a Neutrik ML1 Minilyzer, with the Coarse o/p switch at 10,
and the Fine pot adjusted for +4dBu output level. No load on the terminals (apart from ML1 and 'scope),
but the 600 Ohm switch is in.
Much better! 😄
 
From the "Greening of" list and other mods you can find on the net, I made sure the Fine frequency pot went open circuit; changed the negative return wire of the square wave section to be separate;
changed R3 for 47k (haven't tried 56k); changed C5 to 100uF; changed the caps in the psu and also changed to a LM317; added a meter buffer; then in an attempt to make the supply even quieter I added a 220uF//0.1uF directly across the collectors of Q4 Q5. Not sure if that made any difference.
I didn't bother with the bypass capacitor on the emitter resistor of Q3, as one of the articles said it made things worse! Also didn't try the adding the compound pair suggestion as again other weren't sure it was neccesary, or made things worse.
I then spent a good 15 minutes playing with various settings of the Bias and Feedback pots to give the best results over the whole audio range.
Unfortunately, the Neutrik only goes to 20 kHz, so I can't say wat the distortion is like at 100k, but it looked ok on the scope.
 
From the "Greening of" list and other mods you can find on the net, I made sure the Fine frequency pot went open circuit; changed the negative return wire of the square wave section to be separate;
changed R3 for 47k (haven't tried 56k); changed C5 to 100uF; changed the caps in the psu and also changed to a LM317; added a meter buffer; then in an attempt to make the supply even quieter I added a 220uF//0.1uF directly across the collectors of Q4 Q5. Not sure if that made any difference.
I didn't bother with the bypass capacitor on the emitter resistor of Q3, as one of the articles said it made things worse! Also didn't try the adding the compound pair suggestion as again other weren't sure it was neccesary, or made things worse.
I then spent a good 15 minutes playing with various settings of the Bias and Feedback pots to give the best results over the whole audio range.
Unfortunately, the Neutrik only goes to 20 kHz, so I can't say wat the distortion is like at 100k, but it looked ok on the scope.
Thanks a lot! (y)
 
Some residual distortion may be introduced by the rectifiers driving the level meter. It is the same mechanism that causes real VU meters to add distortion. You can see if this is the case by turning the meter cal down to zero so the meter is effectively out of circuit. If this does give a useful reduction in distortion then it might be worth adding a meter buffer.

Cheers

Ian
 
Some residual distortion may be introduced by the rectifiers driving the level meter. It is the same mechanism that causes real VU meters to add distortion. You can see if this is the case by turning the meter cal down to zero so the meter is effectively out of circuit. If this does give a useful reduction in distortion then it might be worth adding a meter buffer.
Yes, indeed. (y) This is one of the well-documented standard mods for the Heathkit Generator. You can find more information on the pages linked above.
 
Decided to have another tinker with mine and add the constant current mod for Q3 collector.
The distortion is now 0.016% at 1k, 0.023% at 10k, 0.018 at 20k and 0.025 at 100Hz.
These are all unweighted mesurements using a Neutrik ML1 Minilyzer, with the Coarse o/p switch at 10,
and the Fine pot adjusted for +4dBu output level. No load on the terminals (apart from ML1 and 'scope),
but the 600 Ohm switch is in.
Much better! 😄
Can you post a schematic, please for this mod?
Thanks
 

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