# Teensy based synth with CV inputs

**URL:** <https://lookmumnocomputer.discourse.group/t/teensy-based-synth-with-cv-inputs/4491>\
**Category:** DIY STUFF\
**Created:** [January 13, 2022, 3:50pm UTC](https://lookmumnocomputer.discourse.group/t/teensy-based-synth-with-cv-inputs/4491 "2022-01-13T15:50:06Z")\
**Posts on this page:** 1\
**Showing post:** 9

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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:** [July 10, 2022, 11:04am UTC](https://lookmumnocomputer.discourse.group/t/teensy-based-synth-with-cv-inputs/4491/9 "2022-07-10T11:04:54Z")

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Just using Ohm’s law along with basic properties of op amps:

With 3.3 V on R2, the + input is at 3.3\*(180/(300+180)) = 1.2375 V. Same at the - input.

Then the current through R1 is (V1-1.2375)/100k which equals the current through R3, (1.2375-Vo)/33k. So (V1-1.2375)\*33k = (1.2375-Vo)\*100k or Vo = -V1\*33k/100k + 1.2375\*(1+33k/100k) or:

```
Vo = -.33*V1 + 1.646.

```

With V1 = 5 this is -0.004 V. Really 0 V because that’s the limit due to the 3.3 V, 0 V power.

With V1 = -5 this is 3.296 V.

In between the output is linear in the input.

If you’re seeing otherwise there’s either a mistake in the circuit build or a bad op amp.

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