October 25, 2013 - 09:13 am|
Just wanted to say that your write-up here of the modifications to the Heath IG-18 has been really, really helpful in my upgrading the Heath. Combined with Dick Moore's webpage & good assistance I've just completed the re-build and the oscillator seems to work splendidly should (from < 1Hz to 110 kHz) although I still need to check distortion. So - many thanks for setting up this site & documentation!! Greetings, Jesper Mønsted (Denmark)
June 12, 2011 - 07:44 am|
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!
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.
June 11, 2011 - 10:15 pm|
The HA3-2625-5 is available from Newark electronics here:
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.
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?
February 13, 2010 - 08:11 pm|
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