Heathkit Ig-18 Thd Improvement Kit (with Meter Buffer Board)

US $30.00

Pleasanton, California, United States
Jan 29th

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Data Professionals Providing support for legacy Heathkit products. IG-18 THD AND METER Mods There have been lots of articles regarding the improvement of the Heathkit IG-18, but none of them have ever offered a complete kit to make these modifications for the DIY'er. After much urging from my customers, I am now offering a complete kit to upgrade the Heathkit IG-18 based on the many articles that I have been able to review. This same upgrade can be performed on the IG-5218, SG-18, and the SG-5218. These upgrades involve value changes of existing components. There are no modifications to the PC board or added holes. You can at any time, restore the unit back to it's original condition. The added meter buffer board can simply be removed and put back into it's original design. There are NO 'Hacks'! We have discovered that a very few of the last IG-5218's utilized a meter that was manufactured in Japan. This meter, while having the same electrical specifications as the earlier meters, has a smaller physical spacing between the meter terminals. For this reason, we have paid the additional expense to have new PC boards manufactured that will fit both styles of meters. We will constantly strive to improve our products even if it means throwing away perfectly good PC boards. This kit is available in two formats; one complete kit including the parts that need to be changed in the original IG-18, and a supplemental 'meter buffer' only kit for those that have already made the basic changes to the Heathkit IG-18. It comes with a complete step-by-step instruction manual for making the changes. THIS IS FOR A COMPLETE KIT OF PARTS TO MODIFY THE IG-18 INCLUDING THE METER BUFFER BOARD. The meter buffer is a crucial part of improving the THD specification of the IG-18. The non-linear loading of the analog output can create additional harmonic components due to the non-linearity of the diodes used to drive the meter. By adding an additional transistor to increase the impedance of the meter driver and to isolate the rectifier diodes for the meter circuit, you remove this effect from the analog signal path. The IG-18 is a nice Audio generator except when it comes to testing audio gear. The generator as it stands, has a THD spec of below 0.1% which is barely met by the stock IG-18. There are plenty of articles on the net, showing how to improve the distortion spec, making this a decent generator for testing audio gear. Being somewhat of a Heathkit 'purest', I decided to give it a try and see if anyone was actually able to improve on the Heathkit design. The first thing that I discovered is that some of the modifications were actually implemented by Heathkit in the 'follow-on' IG-5218. The IG-5218 is basically the same model (same PC board) in the newer Blue and White colors. The mods consist of changing one resistor and a capacitor on the PC board. Heathkit never did add the meter buffer circuit to the IG-5218. Finally the last digit 'variable' frequency pot must have an 'open' at the end of its travel (also implemented on the IG-5218). The results were impressive. The prototype IG-18 now reads 0.04 % THD on my Heathkit IM-5258 Auto-Balance THD meter on the .3% scale. In addition, I have created a meter buffer board that attaches to the back of the original meter which looks more professional than the typical breadboard modifications that complete the modifications to the IG-18. This kit provides the necessary parts and PC Board to add the following: * Resistor R3 changed to 56k * Capacitor C5 changed to 100 uF * C1 & C2 Changed to 1000 uF * C3 changed to 470 uF * Meter Buffer added Here is a picture of a 'typical' meter buffer installed using a breadboard technique. Here is a picture of the IG-18 Meter Mod board that is included in this Mod kit. Here is the graphed results of an IG-18 with the modifications as plotted on an HP 8903B Audio Analyzer (THD). Here is the graphed results of an IG-18 with the modifications as plotted on an HP 8903B Audio Analyzer (Output Level). Here is a view of a Modified IG-18 FFT spectrum on a 60dB scale at 1 kHz out to 20 kHz. Here is a view of a Modified IG-18 FFT spectrum on a 72dB scale at 1 kHz. The approximate 68dB floor represents a good solid 0.04% THD spec. This is the limit of my spectrum analyzer. The HP8903B, which has noise floor of over 100dB shows the actual THD at 0.0255%. This instrument is much faster and easier to use but does not display an FFT.

Condition:	New: A brand-new, unused, unopened, undamaged item in its original packaging (where packaging is applicable). Packaging should be the same as what is found in a retail store, unless the item is handmade or was packaged by the manufacturer in non-retail packaging, such as an unprinted box or plastic bag. See the seller's listing for full details. ...	Model	IG-18
Country of Manufacture	United States