# AS3340 schematic **URL:** \ **Category:** DIY STUFF\ **Created:** [February 5, 2021, 7:20pm UTC](https://lookmumnocomputer.discourse.group/t/as3340-schematic/2885 "2021-02-05T19:20:04Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![lu.caas](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/lu.caas/32/12420_2.png) [@lu.caas](https://lookmumnocomputer.discourse.group/u/lu.caas)\ **Post date:** [February 5, 2021, 7:20pm UTC](https://lookmumnocomputer.discourse.group/t/as3340-schematic/2885/1 "2021-02-05T19:20:04Z")
Hi guys šŸ˜ Well Iā€™m building my AS3340 PCB and I couldnā€™t find any 360k resistors but this chip needs it somehow. At least thatā€™s what the datasheet says. But I already noticed on some schematics it isnā€™t there? So I just wanted to ask you if someone know if this 360k resistor connected between pin 2 of the as3340 and the VCC is needed. ![SmartSelect_20210205-201704_Adobe Acrobat](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/9/9f0afdc7a3746998998233869df4f23fe743a6fd.jpeg) ---
**Author:** ![eric](https://avatars.discourse-cdn.com/v4/letter/e/898d66/32.png) [@eric](https://lookmumnocomputer.discourse.group/u/eric)\ **Post date:** [February 5, 2021, 7:39pm UTC](https://lookmumnocomputer.discourse.group/t/as3340-schematic/2885/2 "2021-02-05T19:39:41Z")
OK, thatā€™s pin 17, had to look for a while to find that 360K resistorā€¦ It is used to bias the pitch control voltage towards +15V so the CV inputs have a more usual range. So a close enough value will be OK. 330K or 390K will certainly do. Breadboard first šŸ™‚ Or at least, make a provision for putting two resistors in series on the PCB if you ever need it. 330K + 33K = 363K, and thatā€™s close enough (well below the 5% tolerance of resistors when the 3340 was designed) This is a nice way of doing it : ![untitled](https://global.discourse-cdn.com/free1/uploads/lookmumnocomputer/original/2X/1/10ae05c6dd330af42e145a16b001f28b2bf1c83c.jpeg) If you need to put two resistors in series instead that silkscreened one, put them vertically, I let you guess howā€¦ ---
**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:** [February 5, 2021, 7:47pm UTC](https://lookmumnocomputer.discourse.group/t/as3340-schematic/2885/3 "2021-02-05T19:47:06Z")
Think of it as another CV, but a fixed one. And 360k instead of 100k to scale down the effect of it; roughly itā€™s like a +5 V CV with a 100k resistor. Without it everything works, but (about) 5 octaves lower. Some people like to have oscillators that use 0 V for the lowest note they play (and then feed in only positive CV for higher notes), some like 0 V for about middle C (and then use negative CV when they want lower notes). This +15 V and 360k gets you the latter. ---
**Author:** ![lu.caas](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/lu.caas/32/12420_2.png) [@lu.caas](https://lookmumnocomputer.discourse.group/u/lu.caas)\ **Post date:** [February 5, 2021, 7:47pm UTC](https://lookmumnocomputer.discourse.group/t/as3340-schematic/2885/4 "2021-02-05T19:47:12Z")
Oh yeah pin 17 Iā€™m sorry!! Thank you for the explanation, it makes more sense now šŸ™‚ Well okay Iā€™ll try the two resistors in series,ā€¦ But I have to find new resistors šŸ˜… ---
**Author:** ![lu.caas](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/lu.caas/32/12420_2.png) [@lu.caas](https://lookmumnocomputer.discourse.group/u/lu.caas)\ **Post date:** [February 5, 2021, 7:49pm UTC](https://lookmumnocomputer.discourse.group/t/as3340-schematic/2885/5 "2021-02-05T19:49:02Z")
So if I want 0V as the lowest note I can remove it? Because my Midi to CV module starts at 0V for the lowest midi note ---
**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:** [February 5, 2021, 7:59pm UTC](https://lookmumnocomputer.discourse.group/t/as3340-schematic/2885/6 "2021-02-05T19:59:56Z")
Sure, you can always add it in later if you decide you want itā€¦ easier than removing it if you decide you donā€™t. (Also, many MIDI-CV circuits allow you to choose which behavior they do.) ---
**Author:** ![lu.caas](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/lu.caas/32/12420_2.png) [@lu.caas](https://lookmumnocomputer.discourse.group/u/lu.caas)\ **Post date:** [February 5, 2021, 8:01pm UTC](https://lookmumnocomputer.discourse.group/t/as3340-schematic/2885/7 "2021-02-05T20:01:22Z")
Okay okay šŸ˜ As long as the 1V per octave is still there then itā€™s okay šŸ™‚ Iā€™ll look at it later then thanks the the tip ---
**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:** [February 6, 2021, 9:51am UTC](https://lookmumnocomputer.discourse.group/t/as3340-schematic/2885/8 "2021-02-06T09:51:52Z")
> So if I want 0V as the lowest note I can remove it? Define ā€œlowest noteā€. The standard 3340 config outputs ~1 Hz with no CV in, which isnā€™t very useful if you plan to listen to the output. šŸ˜€ See here: > [@Need some help with the kosmo vco w/ tuner. Please! Iā€™ve lost weeks](https://lookmumnocomputer.discourse.group/t/need-some-help-with-the-kosmo-vco-w-tuner-please-i-ve-lost-weeks/691/50): > > One more thing to note is that with the typical resistor/capacitor values, the 3340 is calibrated to behave nicely from ~1 Hz all the way to 20 kHz and beyond, and you have to feed in quite a bit of voltage to get an audible signal. Assuming nominal resistor/capacitor values, the 10k tracking pot set to the middle position, and that I didnā€™t completely screw up my algebra, the CV for a given frequency is: cv = 1.463 \* ln(freq) + 0.239 so for e.g. 440 Hz you need to feed in just over 9 V in toā€¦ The 360k resistor shifts this a few octaves up, into a somewhat more useful range. Note the datasheet circuit is for 15 V; if youā€™re using 12 V supplies you need to adjust this (and a few other values). But itā€™s probably easier to use a coarse tune potentiometer as one CV input, so you can dial in 0V to your liking, as itā€™s done in the simple 1V/Oct oscillator (and many others): > [@Annotated Simple 1V/Oct Oscillator Stripboard](https://lookmumnocomputer.discourse.group/t/annotated-simple-1v-oct-oscillator-stripboard/1267): > > And hereā€™s [the LMNC 3340 stripboard layout](https://www.lookmumnocomputer.com/projects#/cem-3340-diy-simple), with scribbles: See [here](https://lookmumnocomputer.discourse.group/t/annotated-simple-low-pass-filter-stripboard/1266) for the annotated Simple Low Pass Filter stripboard. > I couldnā€™t find any 360k resistors 36 is a standard E24 (5%) value, so shouldnā€™t be that hard to find (see e.g. [tayda](https://www.taydaelectronics.com/catalogsearch/result/?q=360k+ohm)) šŸ™‚ ---
**Author:** ![lu.caas](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/lu.caas/32/12420_2.png) [@lu.caas](https://lookmumnocomputer.discourse.group/u/lu.caas)\ **Post date:** [February 6, 2021, 10:34pm UTC](https://lookmumnocomputer.discourse.group/t/as3340-schematic/2885/9 "2021-02-06T22:34:34Z")
Wow nice so much information! šŸ˜ Thank you a lot, I think it would be better to use a resistor then but the better I could find was a 380k ohm from a PCB I found on the road šŸ¤£ Well I will try this resistor later thanks to everyone šŸ˜‰