How to minimize output offset drift w/o servo?? - Page 2

anatech · 9th November 2006, 03:57 PM

Hi Leolabs,
Do you mean complimentary diff pair?

All those transistors have to be matched together for the lowest distortion and DC drift.

-Chris

Leolabs · 10th November 2006, 02:24 AM

No.No different pairs.Just CE input stages.

anatech · 10th November 2006, 02:30 AM

Hi Leolabs,
I'm sorry. I'm having trouble visualizing that. It's just me.

Do you have an example?

-Chris

Leolabs · 10th November 2006, 08:51 AM

yes.
latest version of Lizi

anatech · 10th November 2006, 02:27 PM

Hi Leolabs,
Thanks, Tandberg style. Never liked it much because it isn't naturally balancing.

You must match the fets closely and couple them thermally. A capacitor in series with R4 would greatly help with offset control. Conversely, you can use an op amp integrator (filter it's output) and use that DC signal to control your offset. It does complicate this circuit but may offer much better control. I would match the fets and couple them in any case.

-Chris

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9th November 2006, 03:57 PM	#11
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Leolabs, Do you mean complimentary diff pair? All those transistors have to be matched together for the lowest distortion and DC drift. -Chris

10th November 2006, 02:24 AM	#12
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	No.No different pairs.Just CE input stages.

10th November 2006, 02:30 AM	#13
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Leolabs, I'm sorry. I'm having trouble visualizing that. It's just me. Do you have an example? -Chris

10th November 2006, 08:51 AM	#14
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	yes. latest version of Lizi

10th November 2006, 02:27 PM	#15
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Leolabs, Thanks, Tandberg style. Never liked it much because it isn't naturally balancing. You must match the fets closely and couple them thermally. A capacitor in series with R4 would greatly help with offset control. Conversely, you can use an op amp integrator (filter it's output) and use that DC signal to control your offset. It does complicate this circuit but may offer much better control. I would match the fets and couple them in any case. -Chris

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