LM3886 without electrolytic feedback capacitor and (hardly) no DC offset voltage - Page 6

danielwritesbac · 10th October 2012, 08:51 PM

Quote:

Originally Posted by Marc Vi.

Why not use the way I proposed? Marc.

With the LM3886, your solution is probably better.

Marc Vi. · 10th October 2012, 10:10 PM

Adjusting the supply voltage on one side in order to trim out the offset voltage is a bad solution for every amplifier.

Marc.

AndrewT · 11th October 2012, 08:55 AM

The output offset should be substantially independent of the supply rail voltages in any opamp style amplifier.

However, a VAS stage without CCS supply/source will change it's Iq when supply voltage changes (both rails changing together), and this changed Iq with push/pull more or less current through the Collector load of the input transistor. This changed collector current will change the offset. This is one of the big disadvantages of a bootstrap feed to the VAS in a P3A (ESP) amplifier.

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10th October 2012, 10:10 PM	#52
Marc Vi. diyAudio Member Join Date: Feb 2004 Location: The Netherlands	Adjusting the supply voltage on one side in order to trim out the offset voltage is a bad solution for every amplifier. Marc.

11th October 2012, 08:55 AM	#53
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	The output offset should be substantially independent of the supply rail voltages in any opamp style amplifier. However, a VAS stage without CCS supply/source will change it's Iq when supply voltage changes (both rails changing together), and this changed Iq with push/pull more or less current through the Collector load of the input transistor. This changed collector current will change the offset. This is one of the big disadvantages of a bootstrap feed to the VAS in a P3A (ESP) amplifier.