This is a pulse shaping circuit, that has three amplifiers: U1, U2, and U3. The shaping amplifier is the 8pin component far right. Both U1 and U2 serve as "coarse gain," which are activated by the switch in the bottom left of the diagram. U3 controls the polarity of the input signal, and is also activated by the switch in bottom left. I would like to remove U3 as I have no need for polarity switching.

U3 is connected to another switch, U7, which is boxed in blue along with U3. My first thought is to simply bypass the blue-outlined portion of the circuit. I would do this by connecting the output of U2 to the R7 and shaping amp input, both boxed in black. I imagine this is not the "proper" way, and would require a few components to properly deliver the output of U2 to the shaping amp input. enter image description here

  • \$\begingroup\$ Are you designing it out, or are you modifying a physical circuit? \$\endgroup\$
    – Aaron
    Apr 21, 2021 at 0:55
  • \$\begingroup\$ I don't see any problem with what you're proposing. Connecting the output of U2 to the input of the 'shaper' and wiper of R7 is exactly what happens when the switch in U7 closes from 'Common' to 'NormOpen', and the output of U3 is simply ignored. \$\endgroup\$
    – brhans
    Apr 21, 2021 at 2:21

1 Answer 1


At a minimum all you need to do is desolder U7 and then jumper from U2.1 to R7 wiper. Once U7 is removed, the output of U3 will not go anywhere.

If you are redesigning this, then remove all the components that you have outlined in blue, and then make the same connection from U2.1 to R7 wiper.

  • \$\begingroup\$ I am redesigning this. Thanks for the suggestion, Aaron. \$\endgroup\$
    – earl
    Apr 21, 2021 at 1:15

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