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Going into action right away. Report in 15 min...
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If you do this little mod make sure you keep R9 at 100-150R.
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Sorry forgot to attach. Just added it.
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Originally Posted by: Russ White  If you do this little mod make sure you keep R9 at 100-150R. Almost there. No space for that cap !!
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if you are using one of our stock trafo make sure it's secondaries are in parallel. Carefully respect phase.
I had to use an under-powered trafo to get 400mv p2p ripple.
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Originally Posted by: Russ White I was able to reproduce your results given that large input ripple.
The good news is I also was able to fix it. :)
There are two ways to fix it, the first is obviously to reduce the input ripple.
The second is to isolate the error amp from the ripple.
This is not quite as simple but very doable. It requires a little trace cutting so it's up to you if you think its worth it.
On the bottom of the board cut the trace from V+ to QP7/QP8 emitters (see attachment)
Then add say 221R from V+ to either emitter pad (they are connected)
Then add a suitably rated (say 25V) 220-1000uf capacitor from either emitter pad to GND observing correct polarity.
When I tried this even with a very high input ripple I had < 50uV ripple on the output.
Worth a shot. :) Its pretty easy.
I will probably add this feature to the next revision. Thanks for making me think a little more deeply about it. YES, nailed it! Now the Placid is true low noise. I'll do the same to the BP. Edited by user Sunday, April 14, 2013 7:49:07 PM(UTC)
| Reason: Not specified avr300 attached the following image(s):  the final cut.JPG (42kb) downloaded 83 time(s).You cannot view/download attachments. Try to login or register.
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Originally Posted by: Russ White if you are using one of our stock trafo make sure it's secondaries are in parallel. Carefully respect phase.
I had to use an under-powered trafo to get 400mv p2p ripple. Yes. black||orange // yellow||red
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Originally Posted by: Russ White Very cool. :) Yes, thank you Russ for your kind help.
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It was my pleasure. I love solving things like this. :)
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Jobs done to the BP as well.
Flat line output now. This is a really important update.
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I actually have an even better improvement coming. I will make the error amp referenced to the output. Already tested it. It works great! Even with 400mv ripple input am getting < 5uV at the output.
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Leak the info here. I'll test it as well (despite that the DAC is in full operation again, I'll gladly take it apart again ;-)
This minds me of the AVCC mod to the B24. Great leap in performance.
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Here is the new circuit as tested. It is not so simple a mod as the one I previously described. It will be best served with a new PCB. Which I also just finished. :) Cheers! Russ Russ White attached the following image(s): Placid_HD_Q.jpg (80kb) downloaded 269 time(s).You cannot view/download attachments. Try to login or register.
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Pretty transparent ;-) Interesting. I'll get it when available.
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Fixed attachment. had a hard time generating the right image. :)
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Thanks. Doesn't seems that difficult to implement.
Will you generate the file with a fraction higher resolution, pls. Tia.
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email me and I will reply with the PDF.
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