# Debugging my Tri-Sine waveshaper

**URL:** <https://lookmumnocomputer.discourse.group/t/debugging-my-tri-sine-waveshaper/2877>\
**Category:** DIY STUFF\
**Created:** [February 4, 2021, 9:42pm UTC](https://lookmumnocomputer.discourse.group/t/debugging-my-tri-sine-waveshaper/2877 "2021-02-04T21:42:28Z")\
**Posts on this page:** 4\
**Page:** 2

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**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\
**Post date:** [September 27, 2022, 9:27pm UTC](https://lookmumnocomputer.discourse.group/t/debugging-my-tri-sine-waveshaper/2877/21 "2022-09-27T21:27:21Z")

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> [@nohar](#):
>
> In yellow, is what comes in the opamp.

In? Or out?

Check voltages on the TL072. Post photos of your build.

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**Author:** ![nohar](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/nohar/32/15516_2.png) [@nohar](https://lookmumnocomputer.discourse.group/u/nohar)\
**Post date:** [September 27, 2022, 9:50pm UTC](https://lookmumnocomputer.discourse.group/t/debugging-my-tri-sine-waveshaper/2877/22 "2022-09-27T21:50:33Z")

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It was one of the inputs. I assumed the were the same, but they are not:

 ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/4/c/4cba6427bf4bc9aaa88621cb0d6e2da13ebf2a60.png)  
These are the two inputs.

A picture of the build

 ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/3X/d/2/d2811b3d2ed37568591de615cce9a55f8a2f6f7d.jpeg)

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<div class="post-metadata">

**Author:** ![analogoutput](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/analogoutput/32/29663_2.png) [@analogoutput](https://lookmumnocomputer.discourse.group/u/analogoutput)\
**Post date:** [September 27, 2022, 10:56pm UTC](https://lookmumnocomputer.discourse.group/t/debugging-my-tri-sine-waveshaper/2877/23 "2022-09-27T22:56:26Z")

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The two inputs should look the same, and should be a sine wave with a small amplitude and a positive offset — so the yellow trace looks kind of like it should, the magenta trace doesn’t.

If the + and - inputs don’t look alike it could mean:

- The op amp is bad
- The op amp power is bad
- The feedback path (from pin 7 to R182 to R181 to pin 6) is bad
- One input pin (or both) is improperly connected to some voltage source instead of to the Q3 and Q4 collectors which are current sources. (Maybe via a short, or a mistake in the PCB.)

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**Author:** ![nohar](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/nohar/32/15516_2.png) [@nohar](https://lookmumnocomputer.discourse.group/u/nohar)\
**Post date:** [September 28, 2022, 10:52am UTC](https://lookmumnocomputer.discourse.group/t/debugging-my-tri-sine-waveshaper/2877/24 "2022-09-28T10:52:49Z")

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All these were good!

The error came from the values of the resistor I wrote on the PCB. I inverted R6 and R19 values when doing that… I guess I won the right to submit a form to the dumbass dept.

Thanks for your time! The investigations helped me understand a little better this circuit

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