UcD amp cant shut off by pulling the tail current

zilog · 5th April 2006, 01:52 PM

I have a UcD amplifier built similar to a schematic I found on the net with standard configuration of the tail pair. As I understand, it should be possible to control the on/off state of the amplifier by letting the bottom end of the tail pair float or not compared to VSS. For my amplifier, this causes one of the output devices to switch at some frequency - and thereby pump the bus at an enormous rate.

Anyone else had this weird problem with an UcD?

zilog · 5th April 2006, 02:05 PM

Never mind, fixed it now - my implementation of the control pulled both emitter resistors and center resistor in the diff pair - the working version pulls only the center resistor.

5th April 2006, 01:52 PM	#1
zilog diyAudio Member Join Date: Oct 2005	UcD amp cant shut off by pulling the tail current I have a UcD amplifier built similar to a schematic I found on the net with standard configuration of the tail pair. As I understand, it should be possible to control the on/off state of the amplifier by letting the bottom end of the tail pair float or not compared to VSS. For my amplifier, this causes one of the output devices to switch at some frequency - and thereby pump the bus at an enormous rate. Anyone else had this weird problem with an UcD?

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5th April 2006, 02:05 PM	#2
zilog diyAudio Member Join Date: Oct 2005	Never mind, fixed it now - my implementation of the control pulled both emitter resistors and center resistor in the diff pair - the working version pulls only the center resistor.

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