There is a simpler way to do this.

Posted by Ralph (M) on December 9, 2015 at 13:20:29

In Reply to: differential input, single ended output posted by rage on December 8, 2015 at 17:17:15:

You can can simply use a single-ended circuit as the input voltage amplifier.

Since you are are not going to be running loop feedback, you could drive the cathode of the tube in addition to driving its grid.

Its not balanced (the cathode input being fairly low impedance), but it is differential in every aspect of the word. So it will accept and process a balanced input.

In order to drive the cathode, you would use an electrolytic capacitor of exactly the value one would use for cathode bypass. You would tie it to pin 3 of the XLR, and the grid to pin 2 of the XLR. If you run single-ended, you would put a jumper between pin 3 and pin 1 of the XLR. Or just let it hang.

Don't laugh till you try it- this was how the original opamps designed by George Philbrick worked way back in the late 1940s. I've been using the technique for years.

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Follow Ups Full Thread

Topic - differential input, single ended output - rage 17:17:15 12/08/15 (17)

RE: differential input, single ended output - rage 17:08:47 01/10/17 (0)

There is a simpler way to do this. - Ralph 13:20:29 12/09/15 (0)

RE: differential input, single ended output - Eli Duttman 17:33:12 12/08/15 (13)

That's not a differential input - Triode_Kingdom 19:11:06 12/08/15 (10)

RE: That's not a differential input - rage 18:44:56 12/10/15 (0)

RE: That's not a differential input - Eli Duttman 21:06:29 12/08/15 (8)

RE: That's not a differential input - Triode_Kingdom 22:45:55 12/08/15 (7)

RE: That's not a differential input - JKT 09:39:10 12/10/15 (0)

RE: That's not a differential input - Eli Duttman 12:13:03 12/09/15 (4)

RE: That's not a differential input - dtut 14:24:30 12/13/15 (3)

RE: That's not a differential input - Eli Duttman 15:22:51 12/13/15 (2)

RE: That's not a differential input - rage 17:24:15 12/20/15 (1)

RE: That's not a differential input - beautox 00:46:38 12/21/15 (0)

RE: That's not a differential input - Stuben 08:56:53 12/09/15 (0)

RE: differential input, single ended output - rage 17:37:00 12/08/15 (1)

RE: differential input, single ended output - Eli Duttman 18:34:45 12/08/15 (0)

RE: differential input, single ended output - JKT 17:26:53 12/08/15 (0)

Follow Ups

There is a simpler way to do this. - Ralph 13:20:29 12/09/15 (0)

There is a simpler way to do this.

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