4069UB triangle waves 40106 - Buffer stages

[volta]

Hi everyone!! 
I'm new to this forum
I've been experimenting with sound circuits based on CMOS, I came across this tutorial from Eliot Williams (Logic Noise)
https://hackaday.com/2015/03/09/logic-noise-sawing-away-with-analog-waveforms/

I'm building an instrument using triangle waves from a 40106 and sending them to a 4069 for buffering. I don't have much knowledge of electronics and am still learning, but I'm thinking of sending each triangle oscillator (3 or more) to a different inverter available on the 4069. connecting a 100k resistor to the input and a 100k resistor to the feedback. Is it a good idea to do it separately? or I should just use one inverter to mix and buffer it all like the active mixer presented here: https://hackaday.com/2015/07/02/logic-noise-ping-pong-stereo-mixers-and-more/
I thought of using them separately because their are going to be so many inverters unused and I'm not thinking to overdriving them.

Should I add 1uf capacitors before the triangle waves enter the 4069? Or is it unnecessary in this case? 
Also, I'm wondering what's the best way to add independent volumes to each oscillator, if it should be before or after the buffer.

Sorry for so many questions, I'm going to continue to experiment with several setups of this. Thank you!

[ianbax]

This could be a case of the blind leading the blind (my electronics knowledge is only gained from experimenting with the circuits on here) but I've worked through the logic noise series (and other sources such as Nicolas Collins Handmade Electronic Music) and built some successful modules so let me try and help - perhaps a more experienced forum member will set me straight if I give bad advice.

I've only breadboarded up the triangle from 40106 rather than done anything finished with it but I *think* if you're mixing them a buffer for each one (i.e. one inverter from the 4069) is essential, otherwise they will interact. Like you said you've got inverters to spare and if I've learned one thing on my electronics journey it's that buffers are good!

From the buffers you can use another inverter from the 4069 as a summing amp (some good mixer circuits here - http://www.all-electric.com/schematic/simp_mix.htm - as Elliot Williams points out in the filter article, you can substitute a 4069 for an op amp where negative feedback is being used and positive terminal is grounded)

I've put together a schematic that *I think* would work - although I haven't tested it!

Apologies for my drafting - I used this online schematic drawing software (https://www.circuit-diagram.org/) and you know I wasn't sure how to draw a potentiometer in a schematic but they're wired as volume controls so, input on one lug, output from the wiper and ground on the other lug.

The one thing you may want to play around with is the output DC blocking capacitor - I think I misread the Logic Noise article and put a huge capacitor in there (10uf I think, maybe it was more) and I ran in to trouble with impendence plugging into a guitar amp (buffered mixer fine) - there's a thread on it!

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[PHOBoS]

[volta]

Thank you ianbax and phobos!!

I experimented both ideas that I talked on the first post to understand them better and I liked the result of using a buffer for each one with 4069!
I breadboard the circuit with 3 oscillators, triangles waves to separates buffers on 4069, and then volumes potentiometers and resistors mixing and output cap. (I changed some things on your image Ianbax to explain this version, thank you for sharing the draft). I tried to use another inverter from the 4069 as a summing amp like you said, but I compared between the two versions and I prefered without it, because when the volumes are all down, I notice a lot of noise on the sound when outputting to my mixer and PA, the circuit sound more quieter and smooth when I don't use that part. I also added decoupling caps on power, 2 caps of 100 uf and 100nf on the power pin of every chip and it helped with the noise a bit.

[ianbax]

No problem - my pleasure. Glad you got it working.

Interesting about the summing mixer - I've used that design to mix the square waves from a 40106 but I suppose with the triangle waves already buffered individually the active mixer is just over-engineering. A passive mixer (as you've built) works just fine and as you say, a lot cleaner.

[ianbax]

and just on the 4069 as op amp - perhaps others may find this thread and find it useful

It crops up in Ellliot Williams' logic noise here:

https://hackaday.com/2015/03/09/logic-noise-sawing-away-with-analog-waveforms/

Where he goes into what makes the unbuffered version work as an amplifier - one with a pleasing distortion curve - so as Phobos says, perhaps not the first choice for a hi-fi (well, relatively) mixer.

Incidentally Nicolas Collins recommends the 4049 chip (which was actually what I've used) and claims they're virtually identical for hacking purposes. If you google a couple of guitar FX forums delve into whether they're different.

The audio-phool also recommends one in this video on active filters

https://www.youtube.com/watch?v=aqfyRUVSq9I

About twelve minutes in he basically says if you need something like an op-amp that's been given a virtual ground 1/2 of VCC then the 4069 is basically that in a chip. That's what attracted me initially - having a single supply and getting to know other CMOS chips in my project it seemed easier than getting into op amps.

Elliot points out that if a design (like a simple filter) is an op amp with the positive terminal tied to ground then the 4069UB (or 4049UB) can substitute in - probably with some unpredictable results!

[Top Top]

I've used 4069UB for filters and mixer uses many times. I built a six channel mixer with 4069 twin T band pass filters on every channel, then a 4069 summing amplifier stage, and even a spring reverb driven and amplified by 4069UB.

They do have a rounded squaring to them that sounds nice. It's not accurate, quiet, or hi fi for sure!

[PHOBoS]

oh right, filters. Now that you mention it I did actually use the 4069 for the RGB Shroom drum.


@ianbax thanks for all the info! I really should look into it a bit more, it's an interesting chip.
I wonder if it could do something interesting for video signals as well, since CMOS is generally very suitable for high frequencies
and video signals also have a rather low amplitude.