Comments for page: Heathkit IG-18 Mods

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Posted by Steve L. June 12, 2011 - 07:44 am
Hi Larry,
Thank you for the kind comment.

I did not notice much hum and the 20-1000Hz distortion measurement was at the floor of the analyzer. It's possible that the folks who dealt with the transformer were actually chasing a ground loop problem.

The new board layout has the power supply section comfortably spaced from the audio circuits. I was also very careful about ground connections, as is reflected in the layout diagrams and schematic.

So I didn't find a reason to change the transformer situation.

Let me know how it goes!

Posted by Larry June 11, 2011 - 11:02 pm
Thanks for link Steve. Regarding the power tran, I note you did not relocate,shield or change to toroid as some others have indicated. Did you see no improvement in doing so?
I have a HP339A so I know what this circuit is capable of doing. Good work.

Posted by Steve L. June 11, 2011 - 10:15 pm
Hi Larry,
The HA3-2625-5 is available from Newark electronics here:
Newark link

The listing is a little confusing but it IS in the DIP package and they have 400 in stock and they will sell quantity-1 for $8.55. Note that after stock is depleted, they will only be available in multiples of 500.

I did not try any other opamps, since I felt confident that this one would work well there (per the original HP design). However, I imagine that there are some high-performance opamps which could match it. This one has 100MHz gain-bandwidth, 35V/us slew rate and works from 15V power supplies.

I will be happy to help if you have any other questions.


Posted by Larry June 11, 2011 - 09:52 pm
Have you a source for the HA3-2625-5 IC?
If not have you tried another low distortion opamp?

Posted by Steve L. February 13, 2010 - 08:11 pm
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