# AS3340 CV input negative voltage **URL:** \ **Category:** DIY STUFF\ **Created:** [January 18, 2021, 2:00pm UTC](https://lookmumnocomputer.discourse.group/t/as3340-cv-input-negative-voltage/2728 "2021-01-18T14:00:24Z")\ **Posts on this page:** 1\ **Showing post:** 10
**Author:** ![Caustic](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/caustic/32/15588_2.png) [@Caustic](https://lookmumnocomputer.discourse.group/u/Caustic)\ **Post date:** [January 18, 2021, 5:49pm UTC](https://lookmumnocomputer.discourse.group/t/as3340-cv-input-negative-voltage/2728/10 "2021-01-18T17:49:11Z")
I wrote a post about summing OpAmp circuits here (showing how the simple mixer worked): > [@LMNC Super Simple Mixer \[Strip Board Layout + BOM\]](https://lookmumnocomputer.discourse.group/t/lmnc-super-simple-mixer-strip-board-layout-bom/97/2): > > Notes on Schematic: The TL072 is a chip which has two operational amplifiers, and this mixer takes advantage of a specific type of Op-Amp circuit called a “Summing Amplifier Circuit”. Tldr; Summing Op-Amp circuits basically mush all the inputs into a single output voltage that is literally the sum of all the other voltages. [tl072] As stated in the instructions, all of your inputs go into pin 2, which is the inverting input of the Op-Amp (the part of the triangle with the - sign). … --- _[View the full topic](https://lookmumnocomputer.discourse.group/t/as3340-cv-input-negative-voltage/2728)._