Comparator oscillation in meter circuit - pollutes audio

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JR.
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Re: Comparator oscillation in meter circuit - pollutes audio

Post by JR. » Sun Sep 03, 2017 1:32 pm

ilya wrote:
Sat Sep 02, 2017 2:10 pm
mediatechnology wrote:
Sat Sep 02, 2017 1:59 pm
I would lower it to 100 nF.
Also bypass the voltage divider node at the non-inverting input.
Be aware of the potential of TL07X latch-up as a follower.
Will do. What would be a better ic for this job? NE553x?
Don't think in terms of brute force. The capacitor will provide a decent low impedance at HF. The op amp won't drive the caps directly and uses series resistance to keep it stable.

JR

ilya
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Re: Comparator oscillation in meter circuit - pollutes audio

Post by ilya » Sun Sep 03, 2017 1:52 pm

Ok. I'm going to modify the current splitter and grounding scheme and see if it helps with the issues. Here's the version with all modifications suggested in this thread:
splitter2.jpg
Does this looks correct?

ilya
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Re: Comparator oscillation in meter circuit - pollutes audio

Post by ilya » Tue Sep 05, 2017 4:38 am

Had a chance to modify the circuit as was suggested. Unfortunately, it didn't help much. I still get the harmonics from comparator oscillation :(

Edit: FOUND IT! This is the comparator coupling to the nearby filter inductor. Gonna see if some screening helps.

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mediatechnology
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Re: Comparator oscillation in meter circuit - pollutes audio

Post by mediatechnology » Thu Sep 07, 2017 6:41 pm

ilya wrote:
Tue Sep 05, 2017 4:38 am
Had a chance to modify the circuit as was suggested. Unfortunately, it didn't help much. I still get the harmonics from comparator oscillation :(

Edit: FOUND IT! This is the comparator coupling to the nearby filter inductor. Gonna see if some screening helps.
Filter inductor? Didn't see that one.
Glad you found it! (We hope.)
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ilya
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Re: Comparator oscillation in meter circuit - pollutes audio

Post by ilya » Fri Sep 08, 2017 1:57 am

mediatechnology wrote:
Thu Sep 07, 2017 6:41 pm
Filter inductor? Didn't see that one.
Glad you found it! (We hope.)
You didn't see it because it's in another part of the circuit, I didn't post a schematic for that. Comparators are physically above the inductors, so the transients were coupling right into inductors. Had to slow chips down with caps, screening didn't work well enough.

BUT the grounding modification did improve the noise situation a lot as well. Thanks for all your comments!

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