THD Improvement kit for IG-18 series audio generators (complete kit) - IGA-18-1

$ 29.95 $ 29.95 29.95 USD

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Let's improve your audio meter.

No need to spend hundreds to upgrade your IG-18!

Many voices, one kit. Lots of articles have suggested improvents to the Heathkit IG-18. But until now, no one offered a complete kit to make these modifications easy for the DIY'er.  We have incorporated the best of those published ideas and now offer a complete kit to help you upgrade your Heathkit IG-18. 

We'll be 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).

Which meter type do you have? ...OK, this kit handles it. We constantly strive to improve our products--even if it means throwing away perfectly good PC upgrade boards. Well, it turns out a very few of the last 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 modify the IG-18.

(Including a Meter Buffer Board.)

This kit assumes that you have not made meter-buffering changes to your IG-18.

This kit is intended to add a meter buffer circuit to your IG-18, and includes all the components necessary to modify the existing boards in the IG-18. The parts included in this kit are: 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

Let's get technical. 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.

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 IG-18 Meter Mod board included in this kit. There, that looks better, doesn't it.

OK, how does it do?

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

Try finding some THD. Go ahead. Try.

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.

Convinced yet?

We thought so.

And only $6 shipping/handling to all US locations. Get on back up there to the top of this page and order yourself one, before we run out.