THD Improvement kit for IG-18 series audio generator test equipment (complete kit) - IGA-18-1

$ 29.95 $ 29.95 29.95 USD

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Let's improve your Heathkit test equipment.

Here's a cost-effective upgrade your IG-18 audio meter.

Many voices, one kit. Many articles have suggested improvements to the Heathkit IG-18. Until now, no one offered a complete test equipment kit to make these modifications easy for the DIY'er. We evaluated the designs, and Heathkit now offers a complete new kit incorporating the best electronics to help you get the best possible performance from your Heathkit IG-18. 

Highly compatible. This upgrade can be performed on the IG-5218, SG-18, and the SG-5218.

Confirm your desired kit format. Our upgrade kit is available in two formats:

  1. A complete kit including the parts that need to be changed in the original IG-18 (this kit), and
  2. A  smaller 'Meter Buffer Only' kit, for owners who have already made the basic changes to the Heathkit IG-18 circuit and now want to add only a meter buffer.  

This kit is for the complete Meter Buffer Board upgrade kit (see below).

Whichever meter type you have ...this kit handles it. We constantly strive to improve our products. It happens some Heathkit IG-5218's use a meter manufactured in Japan. It has the same electrical specifications as the earlier meters, but a smaller physical spacing between the meter terminals.  To ensure compatibility, we've gone the extra mile, and designed and manufactured for you a new PC board that fits both styles of meters.  Either way you're covered.

This kit is the complete kit of parts

to improve the IG-18.

(Including a Meter Buffer Board.)

This kit assumes that you have not made any changes to your IG-18. (Not sure? If you have made changes or have a late-model unit where the changes were in the redesigned product, then, R1 would be 56kOhms and C5 is 100uF. If not, you definitely want this "complete kit.)

This kit adds a meter buffer circuit to your IG-18, and also includes all the components necessary to modify the existing boards in the IG-18. This kit provides the necessary parts and PC Board to replace/upgrade/install the following:
 * Resistor R1 changed to 56k
 * Capacitor C5 changed to 100 uF
 * C1 & C2 changed to 1000 uF
 * C3 changed to 470 uF
 * Meter Buffer (new printed circuit board you will build and install)

Why this new test equipment kit? Let's get technical. The meter buffer is a crucial part of improving the THD specification of the Heathkit 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.

Let's check out your choices.

Are you ready to go pro?

Odoo - Sample 1 for three columns

Wrong choice: Cheesy homebrew breadboard.

Here's a typical meter buffer installed using a breadboard technique. (Or maybe your kid brother did this for you.)

Odoo - Sample 2 for three columns

Right choice: Official Heathkit PCB.

Here's the Heathkit IG-18 Meter Mod board in this kit. Looks better, doesn't it.

How does it perform?

Let's see some proof.

THD: Improved.

Here's the graph of an IG-18 with the modifications as plotted on an HP 8903B Audio Analyzer (THD).

RMS Output: Flat.

Here's the graph of an IG-18 with the modifications as plotted on an HP 8903B Audio Analyzer (Output Level).
Odoo - Sample 1 for three columns

Gosh that's flat.

Here's a view of a Modified IG-18 FFT spectrum on a 60dB scale at 1 kHz out to 20 kHz.

Odoo - Sample 2 for three columns

Just try finding some THD.

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 our spectrum analyzer.


We thought so.

Just go to the top of this page and order yourself one, before we run out.