AD3208 squeal and pop!

[WorkBench]

I built the AD3208 from GGG years ago, and I love it, but it has this issue where whenever my furnace turns on, or another power surge happens, it pops and starts to squeal, and the output is lowered.  I have to switch it on and off again to make it work, and when I do, I get a loud pop.  Any thought?  Thank you.

I did put a 1meg drop down resistor from the input to ground with no avail. So.......?

Chris

[Dave W]

i had a similar problem with an ad80 i built some years back. try a small resistor; 100R or so; in series with the output. that fixed it for me. your results may vary but it is simple enough to do and worth a try.

[WorkBench]

Thanks Dave.  I will give it a try right now.  Could you explain to me what this is doing exactly?  Is it creating a gate that won't allow for DC leakage or something?

Chris

[Dave W]

it isolates the output.
in my case when there was a surge in the house i got a pop (not too loud, iirc) and lowered output but no squeals. and the loud pop when when switching it on/off again.
hope the R thing works for you. keep us posted.
and.... go to GEO and read the article "what are all those parts for?"

[WorkBench]

Practiced at my rhythm guitarists house last night, and no problems.     thanks! I did get a slight pop once when the fridge kicked on, but nothing like before.

So, this resistor isolates the output from what exactly.  DC?

Chrus

[Dave W]

quote from the article mentioned above: "This same resistor isolates the opamp output from highly capacitive loads that could make the opamp unstable, and prevents overcurrents from damaging the opamp, if needed."
go to GEO and click on the "circuit sweepings" link in the menu on the left. good reading!
glad to hear this helped you! 

[WorkBench]

Cool.  Sorry.  Forgot about the article.  Will read for sure.  Thanks again!

Chris