# Octave switch for simple CEM3340 Oscillator? **URL:** \ **Category:** KOSMO MODULES\ **Created:** [April 25, 2020, 10:01pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737 "2020-04-25T22:01:56Z")\ **Posts on this page:** 18\ **Page:** 2
**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:** [April 28, 2020, 8:36pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/21 "2020-04-28T20:36:38Z")
They’re all variants of the TL072 and the ones in PDIP packaging probably are all okay. Actually I have to admit I’ve never thought to concern myself with which version I’m using, aside from packaging (DIP vs SOIC). If I want DIP TL072s I get them from Tayda and looking closely at the listing I see they’re TL072CP. I suppose someday I might find myself with a circuit where it matters what VIOmax is but it hasn’t happened yet. I’m pretty sure I’ll never need to worry about whether my module will operate down to -55°C or not. > **[TL072IP-Texas-Instruments-datasheet-8317744.pdf](https://datasheet.octopart.com/TL072IP-Texas-Instruments-datasheet-8317744.pdf)** > > 896.85 KB ---
**Author:** ![fredrik](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/fredrik/32/682_2.png) [@fredrik](https://lookmumnocomputer.discourse.group/u/fredrik)\ **Post date:** [April 29, 2020, 8:09am UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/22 "2020-04-29T08:09:56Z")
(tip: TIs site is well organized, and tends to have more information than some random datasheet copy elsewhere 😃 And you can usually guess the URL: [https://www.ti.com/product/TL072](https://www.ti.com/product/TL072) (click or scroll down to “Ordering & quality” to see the variants currently in production from TI, but note that there are other manufacturers too that may use other codes). And as you say, unless otherwise noted in the schematics/BOM, anything in the right package works.) ---
**Author:** ![Dud](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/dud/32/610_2.png) [@Dud](https://lookmumnocomputer.discourse.group/u/Dud)\ **Post date:** [June 12, 2020, 7:06pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/23 "2020-06-12T19:06:33Z")
I want to add the Octave switch to a new VCO, if i have only 3 positions with my rotary switch, my Ref value must be 2V instead 4V 1V per octave, position 1 : direct to GND = normal tune, position 2 : 10K = + 1 oct position 3 : 10K + 10K = +2 oct so 3 positions for 2V ref please tell me if it’s a good deduction or not ---
**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:** [June 12, 2020, 7:11pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/24 "2020-06-12T19:11:34Z")
You could put 20k below position 1 and use 4V. ![Screenshot from 2020-06-12 15-13-30](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/c/ce3c1355d121fea3b3b484c8a9a8e91592f608c7.png) (edit) or probably better, put 20k above the third position, then you get 0, 1, and 2V. ---
**Author:** ![antoine.pasde2](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/antoine.pasde2/32/326_2.png) [@antoine.pasde2](https://lookmumnocomputer.discourse.group/u/antoine.pasde2)\ **Post date:** [June 12, 2020, 7:12pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/25 "2020-06-12T19:12:47Z")
Yes, that will work. Don’t forget to closely match your resistors. You could also use 4V and make each position change by two octaves if you want to cover a larger range. ---
**Author:** ![Dud](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/dud/32/610_2.png) [@Dud](https://lookmumnocomputer.discourse.group/u/Dud)\ **Post date:** [June 12, 2020, 7:17pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/26 "2020-06-12T19:17:37Z")
thank you ! and there is no contraindication to lower the Ref to 2V with the LM4040 and the trimmer pot ? ---
**Author:** ![antoine.pasde2](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/antoine.pasde2/32/326_2.png) [@antoine.pasde2](https://lookmumnocomputer.discourse.group/u/antoine.pasde2)\ **Post date:** [June 12, 2020, 7:21pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/27 "2020-06-12T19:21:54Z")
You can use the same circuit as in the #1222 VCO, the trimmer will just be closer to the middle of its course. ![image](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/e/e504fbb5c4ce13ea2a6d0715da19f5520cc36b17.png) EDIT: crossed out the 4V and added the 2V ---
**Author:** ![Dud](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/dud/32/610_2.png) [@Dud](https://lookmumnocomputer.discourse.group/u/Dud)\ **Post date:** [June 12, 2020, 7:21pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/28 "2020-06-12T19:21:57Z")
yes thx but there is no more position without octave (to GND) ---
**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:** [June 12, 2020, 7:26pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/29 "2020-06-12T19:26:25Z")
20k above third position instead: ![Screenshot from 2020-06-12 15-13-30](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/4/4e9404886e377cd0d3bb4c93cf0cfdb03ad39ba7.png) but sure, trimming 2.1V off the 4.1V reference works too. ---
**Author:** ![Dud](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/dud/32/610_2.png) [@Dud](https://lookmumnocomputer.discourse.group/u/Dud)\ **Post date:** [June 12, 2020, 7:27pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/30 "2020-06-12T19:27:38Z")
Yes ! 2 solutions now, thanks guys ! ---
**Author:** ![antoine.pasde2](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/antoine.pasde2/32/326_2.png) [@antoine.pasde2](https://lookmumnocomputer.discourse.group/u/antoine.pasde2)\ **Post date:** [June 12, 2020, 7:35pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/31 "2020-06-12T19:35:23Z")
> [@analogoutput](#): > > trimming 2.1V off the 4.1V reference works too Probably just a typo, but for clarity, you need to get 2.0V, not 2.1V. ---
**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:** [June 12, 2020, 7:58pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/32 "2020-06-12T19:58:28Z")
Yes, so trimming 2.1V off 4.1V gets you to 2.0V. ---
**Author:** ![antoine.pasde2](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/antoine.pasde2/32/326_2.png) [@antoine.pasde2](https://lookmumnocomputer.discourse.group/u/antoine.pasde2)\ **Post date:** [June 12, 2020, 8:15pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/33 "2020-06-12T20:15:34Z")
Ah! Not what I understood. ---
**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:** [June 13, 2020, 5:00pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/34 "2020-06-13T17:00:02Z")
Thinking about a standalone octave switcher, one with a ±5V range. Any reason not to use something like the Performance Oscillator’s switch, but with a ~~LM4040AIZ-10.0~~ and no trimmer to provide a ~~+10V~~ reference? And then subtract half the reference voltage using a differential amplifier. _Edit:_ No, wait. An LM4040AIZ-5.0, to provide steps of half a volt from 0 to 5V. Then a differential amplifier with a gain of 2. ---
**Author:** ![Farabide](https://avatars.discourse-cdn.com/v4/letter/f/ecc23a/32.png) [@Farabide](https://lookmumnocomputer.discourse.group/u/Farabide)\ **Post date:** [December 5, 2020, 5:24pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/35 "2020-12-05T17:24:00Z")
Is there a 4040 variant the can manage 1v steps? Im seeing far too much arithmetic gentleman (Math in the USA im lead to believe) ---
**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:** [December 5, 2020, 6:34pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/36 "2020-12-05T18:34:12Z")
LM4040 is a voltage reference, in and of itself it doesn’t provide steps. What you need for 1V steps is a voltage reference for some integer number of volts and then resistors to divide that down into 1V steps. The LM4040 comes in 2.048 V, 2.5 V, 3 V, 4.096 V, 5 V, 8.192 V, and 10 V variants, so the 3V, 5V, and 10V versions would seem to best to use. However, any can be used with a trimmer to adjust the voltage down to, for example, 4.0 or 8.0 V. And in fact, to compensate for imprecision elsewhere — for instance, a mismatch between the CV and octave switch input resistors at the CV mixing stage — you might want to deliberately make the steps slightly smaller or larger than 1.0 V (but still equal), in which case starting with a larger voltage and trimming it down is your best course. ---
**Author:** ![Farabide](https://avatars.discourse-cdn.com/v4/letter/f/ecc23a/32.png) [@Farabide](https://lookmumnocomputer.discourse.group/u/Farabide)\ **Post date:** [December 6, 2020, 2:08am UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/37 "2020-12-06T02:08:26Z")
Many thanks @analogoutput. This made things a lot clearer. ---
**Author:** ![YMNK](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/ymnk/32/23992_2.png) [@YMNK](https://lookmumnocomputer.discourse.group/u/YMNK)\ **Post date:** [June 12, 2021, 1:46pm UTC](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737/38 "2021-06-12T13:46:39Z")
Was looking to make a new CEM3340 oscillator with the octave switch. This thread answered all my question. That’s amazing, thanks. [Previous page](https://lookmumnocomputer.discourse.group/t/octave-switch-for-simple-cem3340-oscillator/737.md?page=1)