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ua726 analysis
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author ua726 analysis
ok, so i finally got my hands on some of these. heres what it does:

and a zoom into the interesting bits:

im going to run some more tests to verify, but all in all this doesnt look good. there is a fair bit of leakage on the low end, and the high end rolls off somewhat early. its not as good as the PMP4201 or THAT300's ive tested, but not as bad as my recent work with the LM13700.

as for thermal regulation, its pretty poor.

i was running this with +/-15V rails, an 82k Tadj resistor, and 5uA of reference current.
ok, ran some more tests on a different unit, this time covered in foam to help insulate it from the heatgun even more. i wanted to check if the heatgun was causing thermal gradients.

you can see a very similar shape on a global scale. slightly better drift, which can be seen in the zoom-in:

the linear shift is the same as in the last one (-0.7% - bias current is 5uA), but the slope is better (by at least a factor of 2). the slope shift is still pretty bad. its possible the offset is some external circuitry error, but not likely, as its the same opamps and resistors i have been using for my other tests that did not show these errors. i might run some tests to rule that out.

in any event, the low end leakage isnt good, and the high end emitter resistance is also not very good. the thermal regulation might be improved by using a current source in place of the temperature setting resistor, as the value of this resistor sets the gain of the feedback loop. some HF compensation might be required if the gain is pushed up too high, though. all in all, given the cost of this part, i would not reccomend it.
ok, i found the culprit for the offset: 2 resistors drifting in opposite directions by .01%. so the temperature drift is due to poor thermal regulation of the ua726, but the 0.7% offset drift is external to the ua726.
good stuff.

just ooi were your test subjects original Fairchilds? I had some more recent Korean versions a while back, they seemed to work ok, but I didn't do any temperature testing.
good question, im not sure if they are originals. they have gold plated legs, and the top says:


it looks identical to this image i found online:

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