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From: eburton@buphy.bu.edu (Erich Burton)
Newsgroups: rec.radio.amateur.homebrew,sci.electronics
Subject: Re: schematic for audio T pad?
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Date: 24 Nov 93 18:48:03 GMT
References: <mac.753942730@depot.cis.ksu.edu.cis.ksu.edu>
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mac@cis.ksu.edu (Myron A. Calhoun) writes:
>Can anyone please show me the schematic of a "T pad" for remote-
>control.  I know that a T pad uses at least two variable pots
>and probably keeps the input impedance relatively constant, but
>I haven't been able to re-invent the circuit by diddling around.



Here is an L-pad.  The pots are ganged (ie, they have the same shaft)
and are set up so that impedance seen at the input remains constant.
The letters "a" and "b" indicate where the wipers are for (a) maximum output
and (b) minimum output.


o--------/\/\/\/\/\/\--------
	 a   ^      b
input        |_________________________________o        output
                      |    
                      |         
                      |          <   a
                      |           >
                      |________> <
                                  >
                                 <
                                  >
                                 <   b
                                  |
o_________________________________o____________o


And below is a T-pad, which uses three ganged pots to keep the input
and output impedance constant while varying the voltage divider ratio:


o--------/\/\/\/\/\/\--------           --------/\/\/\/\/\/\--------o
         a   ^      b                           b     ^    a
input        |________________________________________|             output
                      |
                      |
                      |          <   a
                      |           >
                      |________> <
                                  >
                                 <   b
                                 |
o________________________________o__________________________________o



I think that's the basic idea anyway.  I hope this helps.

						-Erich

------------------------------------
Erich Burton -- eburton@buphy.bu.edu
Undergraduate Laboratory Coordinator
Boston University Physics Department