lm3886 oscillates with preamp

ivant · 30th March 2009, 08:25 AM

Hope someone can help with my problem. The chipamp.com lm3886 kit works fine when connected to an ipod or 0404usb soundcard. However, when i connect my preamp to it, the lm3886 oscillates. It only happens when I have the volume knob either at fully clockwise or anticlockwise. Anything inbetween is fine. The oscillation happens regardless of load being connected. I get around 1.5vdc and 4.5vac at the outputs during the ocsillation. I can't find anything on the preamp out wih my multimeter.

AndrewT · 30th March 2009, 06:49 PM

does the chipamp.com implementation have an RF filter on the input and a Zobel or Thiele network on the output?

ivant · 31st March 2009, 02:30 AM

No filter on the input. Zobel is present on the output. Feedback cap is used in the build. If there's no problem when connected with other sources, I assume the problem to be with the preamp instead?

AndrewT · 31st March 2009, 07:22 AM

No filters at all on the input?
RF filter attenuates the very high frequencies that may instigate instability in the amplifier.
LF filter blocks the DC from entering and attenuates the very low frequency that can cause LF instability.

ivant · 31st March 2009, 03:35 PM

The kit only has a 1k resistor in series and a 22k resistor tied to ground on the input. I'll see if the filters solve the problem. Thanks

30th March 2009, 08:25 AM	#1
ivant diyAudio Member Join Date: Mar 2009	lm3886 oscillates with preamp Hope someone can help with my problem. The chipamp.com lm3886 kit works fine when connected to an ipod or 0404usb soundcard. However, when i connect my preamp to it, the lm3886 oscillates. It only happens when I have the volume knob either at fully clockwise or anticlockwise. Anything inbetween is fine. The oscillation happens regardless of load being connected. I get around 1.5vdc and 4.5vac at the outputs during the ocsillation. I can't find anything on the preamp out wih my multimeter.

30th March 2009, 06:49 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	does the chipamp.com implementation have an RF filter on the input and a Zobel or Thiele network on the output? __________________ regards Andrew T.

31st March 2009, 07:22 AM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	No filters at all on the input? RF filter attenuates the very high frequencies that may instigate instability in the amplifier. LF filter blocks the DC from entering and attenuates the very low frequency that can cause LF instability. __________________ regards Andrew T.

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31st March 2009, 02:30 AM	#3
ivant diyAudio Member Join Date: Mar 2009	No filter on the input. Zobel is present on the output. Feedback cap is used in the build. If there's no problem when connected with other sources, I assume the problem to be with the preamp instead?

31st March 2009, 03:35 PM	#5
ivant diyAudio Member Join Date: Mar 2009	The kit only has a 1k resistor in series and a 22k resistor tied to ground on the input. I'll see if the filters solve the problem. Thanks

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