Will this work as a differential stage?

martyh · 8th February 2009, 08:37 PM

Probably a silly question but would this work to get a low impedance differential drive?
Thanks,
Marty

EC8010 · 8th February 2009, 08:48 PM

Not terribly well, I think. The cathode followers are fine but the CCS isn't. Think about what would happen if the signal currents in the two valves were not equal - a very large signal voltage would develop across the CCS. What you'd really like is a current mirror in the cathodes.

martyh · 8th February 2009, 11:01 PM

Thanks, I guess it was a silly question. A search on the forum for “current mirror” turned up plenty of threads where the idea I just drew was discussed at length.

EC8010 · 9th February 2009, 07:13 AM

You're welcome.

ErikdeBest · 9th February 2009, 07:54 AM

Hi Martyh

The circuit you are proposing is a differential cathode follower !? I had not heard of it until recently, when it was extensively discussed in this thread

Erik

8th February 2009, 08:37 PM	#1
martyh diyAudio Member Join Date: Feb 2004 Location: Wisconsin	Will this work as a differential stage? Probably a silly question but would this work to get a low impedance differential drive? Thanks, Marty

8th February 2009, 08:48 PM	#2
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	Not terribly well, I think. The cathode followers are fine but the CCS isn't. Think about what would happen if the signal currents in the two valves were not equal - a very large signal voltage would develop across the CCS. What you'd really like is a current mirror in the cathodes. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

9th February 2009, 07:13 AM	#4
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	You're welcome. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

9th February 2009, 07:54 AM	#5
ErikdeBest diyAudio Member Join Date: Mar 2003 Location: Itoculo	Hi Martyh The circuit you are proposing is a differential cathode follower !? I had not heard of it until recently, when it was extensively discussed in this thread Erik __________________ my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!

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8th February 2009, 11:01 PM	#3
martyh diyAudio Member Join Date: Feb 2004 Location: Wisconsin	Thanks, I guess it was a silly question. A search on the forum for “current mirror” turned up plenty of threads where the idea I just drew was discussed at length.

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