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It is currently 20 Jul 2018, 02:03

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PostPosted: 09 Jul 2018, 01:33 
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Joined: 26 Dec 2016, 03:46
Posts: 53
Location: Bayarea
I have a third module of the same circuit that I use for experiment and change parts to develop the board. Today, out of desperation, I just put that module in place of the bad module, IT WORKS!!! BUT when I put the bad module on the test stand, it tested out fine again!!!

When I built the pcb, I built in batch of 6. I measure every single resistor, every single capacitor in the signal path before putting it in. I was very careful. For the life of me, I don't know what went wrong with the bad module. ALL DC voltage measured out correct, tested out to be absolutely stable. There is nothing wrong other than measure 0.012%THD compare to all the others that are in 0.004% or lower. And that happens only in the amplifier chassis, not even on the test stand.

This starting to go into X-Files!!!! I am going to just put the third module in and take my time to look at the bad one. I am running out of patience.

Again sorry for the ranting, got nobody to vent to, can't tell my big boss as she'll just give me a blank look!!!


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PostPosted: 15 Jul 2018, 04:07 
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Joined: 26 Dec 2016, 03:46
Posts: 53
Location: Bayarea
Been putting in quite a bit of hours. Made a lot of inroad into the problem. The grounding is very critical for high current device like power amp. even with double sided 2oz copper ground plane, moving the soldering point for the front end reference makes a difference. Less than 1" can cause problem even on a solid plane. Still have observation that doesn't make sense, but it's a big improvement already.

High current circuit is very tricky, just a little imperfection can cause the THD reading double or tripple when getting down to 0.005% at 15K or 20KHz.


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