# Properly terminate unused op amp **URL:** \ **Category:** DIY STUFF\ **Created:** [August 29, 2020, 9:04pm UTC](https://lookmumnocomputer.discourse.group/t/properly-terminate-unused-op-amp/1711 "2020-08-29T21:04:37Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![stmllr](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/stmllr/32/5055_2.png) [@stmllr](https://lookmumnocomputer.discourse.group/u/stmllr)\ **Post date:** [August 29, 2020, 9:04pm UTC](https://lookmumnocomputer.discourse.group/t/properly-terminate-unused-op-amp/1711/1 "2020-08-29T21:04:37Z")
I’m creating a stripboard layout from the [Befaco Output v3 schematics](https://befaco.org/docs/Out/Output_V3_Schematic.pdf). The CUE-IN can be controlled using a TL072 based inverting amp. The second op amp of this chip is left unused (the schematic does not mention it). [North Coast Synthesis](https://northcoastsynthesis.com/news/design-mistakes-in-synth-schematics/) suggests not to leave it unused, but instead > “connect its inputs to voltages that would be reasonable for those inputs if the section were being used. For an op amp the best thing to do is probably hook it up as a unity buffer buffering 0V: that is, the output connected to the negative input and the positive input to 0V.” Like this, right? ![terminate-op-amp](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/b/b38f4c2ab50bcb9c7e1b3ba0ed456c1231bd4a32.png) Does this apply to the unused op amp of the Befaco module? Or is there a better design? EDIT: To be more precise: is there a better design when the first op amp of the chip is used as inverting amp? ---
**Author:** ![Bitnik](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/bitnik/32/274_2.png) [@Bitnik](https://lookmumnocomputer.discourse.group/u/Bitnik)\ **Post date:** [August 29, 2020, 9:06pm UTC](https://lookmumnocomputer.discourse.group/t/properly-terminate-unused-op-amp/1711/2 "2020-08-29T21:06:46Z")
That’s how you terminate an unused op amp. ---
**Author:** ![Bitnik](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/bitnik/32/274_2.png) [@Bitnik](https://lookmumnocomputer.discourse.group/u/Bitnik)\ **Post date:** [August 29, 2020, 9:26pm UTC](https://lookmumnocomputer.discourse.group/t/properly-terminate-unused-op-amp/1711/3 "2020-08-29T21:26:05Z")
> [@stmllr](#): > > is there a better design when the first op amp of the chip is used as inverting amp? If you wanted a non-inverted version of the output I suppose you could use the second op amp to invert it back. Is that what you had in mind? ---
**Author:** ![telec16](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/telec16/32/4510_2.png) [@telec16](https://lookmumnocomputer.discourse.group/u/telec16)\ **Post date:** [August 29, 2020, 9:36pm UTC](https://lookmumnocomputer.discourse.group/t/properly-terminate-unused-op-amp/1711/4 "2020-08-29T21:36:55Z")
You can find more details on how to connect unused opamp here: [http://forums.parallax.com/discussion/download/96248&d=1350228174](http://forums.parallax.com/discussion/download/96248&d=1350228174) But yeah, you should connect it in follower configuration, with the non-inverting input at the middle of your power supply. ---
**Author:** ![Jos](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/jos/32/151_2.png) [@Jos](https://lookmumnocomputer.discourse.group/u/Jos)\ **Post date:** [August 29, 2020, 9:58pm UTC](https://lookmumnocomputer.discourse.group/t/properly-terminate-unused-op-amp/1711/5 "2020-08-29T21:58:32Z")
Actually it is recommended not to do this. Have a look at paragraph 4.2.1 of this [texas instruments application report](http://forums.parallax.com/discussion/download/96248&d=1350228174). ---
**Author:** ![stmllr](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/stmllr/32/5055_2.png) [@stmllr](https://lookmumnocomputer.discourse.group/u/stmllr)\ **Post date:** [August 29, 2020, 10:02pm UTC](https://lookmumnocomputer.discourse.group/t/properly-terminate-unused-op-amp/1711/6 "2020-08-29T22:02:44Z")
> If you wanted a non-inverted version of the output I suppose you could use the second op amp to invert it back. Is that what you had in mind? No. The signal is inverted back by a NE5532 driven op amp (used for headphone out). Just looking for the right way to terminate the unused op amp ---
**Author:** ![Bitnik](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/bitnik/32/274_2.png) [@Bitnik](https://lookmumnocomputer.discourse.group/u/Bitnik)\ **Post date:** [August 29, 2020, 10:10pm UTC](https://lookmumnocomputer.discourse.group/t/properly-terminate-unused-op-amp/1711/7 "2020-08-29T22:10:07Z")
> [@Jos](#): > > Actually it is recommended not to do this. Have a look at paragraph 4.2.1 of this [texas instruments application report](http://forums.parallax.com/discussion/download/96248&d=1350228174). The examples pertain to a single rail system. I don’t know whether that applies in this query, but the example labelled “good” is equivalent to connecting the non-inverting input to ground on a dual rail system such as Eurorack or Kosmo. ---
**Author:** ![stmllr](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/stmllr/32/5055_2.png) [@stmllr](https://lookmumnocomputer.discourse.group/u/stmllr)\ **Post date:** [August 29, 2020, 10:12pm UTC](https://lookmumnocomputer.discourse.group/t/properly-terminate-unused-op-amp/1711/8 "2020-08-29T22:12:00Z")
> [@Jos](#): > > Actually it is recommended not to do this. Have a look at paragraph 4.2.1 of this [texas instruments application report](http://forums.parallax.com/discussion/download/96248&d=1350228174). But paragraph 4.2.1 says: > Good: This is the minimum recommended circuit configuration. The noninverting input is tied to a potential between the positive and negative rail, or to ground in a split supply system. Virtual ground may already exist in the system, making the resistors unnecessary. The op-amp output is also at virtual ground (or ground in a split supply system). Eurorack power supply is a split supply system. So I guess it is fine. This kind of circuit is also mentioned as proper implementation in Figure 3 of [http://forums.parallax.com/discussion/download/96248&d=1350228174](http://forums.parallax.com/discussion/download/96248&d=1350228174) ---
**Author:** ![Jos](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/jos/32/151_2.png) [@Jos](https://lookmumnocomputer.discourse.group/u/Jos)\ **Post date:** [August 29, 2020, 10:25pm UTC](https://lookmumnocomputer.discourse.group/t/properly-terminate-unused-op-amp/1711/9 "2020-08-29T22:25:11Z")
In the NO scenario: > All the designer has accomplished is to ensure that the op amp hits a rail, and stays there. This can cause self-heating and increased power consumption. By “hitting the rail” I assume here hitting gnd is meant. Why would that lead to self heating and increased power consumption? ---
**Author:** ![telec16](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/telec16/32/4510_2.png) [@telec16](https://lookmumnocomputer.discourse.group/u/telec16)\ **Post date:** [August 29, 2020, 10:37pm UTC](https://lookmumnocomputer.discourse.group/t/properly-terminate-unused-op-amp/1711/10 "2020-08-29T22:37:33Z")
Oops I forgot to mention that the examples are for single supply opamp! In dual supply you should not connect the non-inverting to +12V or -12V, because when the output “hit the rail”, it consumes more power than being in the middle (gnd for dual supply), and also for the obvious issues if you opamp is not rail-to-rail.