Cancelling DC Offset in a bipolar Opamp - Page 2 - diyAudio
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Old 2nd May 2008, 10:19 AM   #11
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by cliffforrest
I couldn't see the OP types - if FET input you don't need to muck about with matching source impedences.
he didn't and gets 50mV to 2mV variation in output offset.
Now that he has matched he reports an improved offset
Quote:
went to spare millivolt
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Old 2nd May 2008, 11:36 AM   #12
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Sorry, Andrew, I should have read the thread before commenting!

My edit crossed with your post.

I stand by what I said about the impedance - keep the pot low and replace the 1M6 with a T network to give the appropriate range.

Cliff
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Old 2nd May 2008, 02:18 PM   #13
ygg-it is offline ygg-it  Italy
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Default re

Hi thanks for the advice.

What C value do you suggest from the wiper to GND ?
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Old 3rd May 2008, 07:37 AM   #14
ygg-it is offline ygg-it  Italy
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Default capacitor

I have tried from 10nF till 150nF.
The sound comes little "closed" so I will give up of the Capacitor and I will stay with the original circuit.
Thank you all for advices.
Ciao!
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Old 3rd May 2008, 08:03 AM   #15
AndrewT is offline AndrewT  Scotland
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post a final schematic and final cold to hot offset values for your creation.
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Old 5th May 2008, 04:35 PM   #16
ygg-it is offline ygg-it  Italy
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Default done!

Done!

http://ygg-it.tripod.com/id15.html
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Old 5th May 2008, 04:47 PM   #17
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Default Re: capacitor

Quote:
Originally posted by ygg-it
I have tried from 10nF till 150nF.
The sound comes little "closed" so I will give up of the Capacitor and I will stay with the original circuit.
Thank you all for advices.
Ciao!
I would have 100 nF or so just for not letting in noise from the power supply.
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