Thursday, August 2, 2018

40106 Quad opto coupled VCO--Lunetta Lives!

All hail Lunetta Synthesis--the CMOS anything-goes way of thinking about Audio DIY?



One thing that appeals: Stanley Lunetta is from the California Central Valley, same as me--from my reading his studio was about 40 miles from where I was recording back in the day.

Does this prove that we Central CA folks aren't all farmers and politicians?  Does it need to be proven? Growing up I remember a great music scene, at least in the 70s. Makes sense--there was very little else (legal) to do!

OK: In honor of Lunetta Synthesis and all Central Valley artists I decided to fab a quad VCO one of the great CMOS chips, the 40106.

I've messed with this chip before but this was my first attempt at doing something this, well, VCOish.

I went through a few generations of experimenter boards by designing in Eagle, and sending off to EASYEDA for a test fab.  I almost have given up on perf'ing things. It's faster and easier for me to have boards fab'd abroad, sent back to the US, and if they don't work, try to kludge them into operation or just toss them and start over.

OK, The board I ended up using for this is here (on my website) tests working.  Yeh!

FREEBEE ALERT, comment if you are interested in one of these experimenter boards (I have way more at this point then I will ever use) and I will send a few of you one free!  Yes Free!!!  Wait free?  Um yes, free!!  Open source, baby!  Until I run out....


Here's the schematic....you can get a zip of this in Eagle format on my site.



Ok so what is up with R1, R2, R3, R4?  You can use the values in the schemo above and call it a day, but what fun would that be?  Instead I replaced these resistors with the "resistor side" of the optos: four optocouplers bought surplus from Electronics Goldmine, but for this design go ahead (!!) and use whatever vactrol or pot or resistor or thingy you care to use. Or just use a resistor? Try different things. See what you like. Experimentation is the key here, have fun!!!!

Using the optos, I could get pretty decent (but highly non-linear) output from very slow LFO, maybe 2hz? to about 12K and up.  Good enough for F/X.

EZ buffer circuit fragment used for the optos


One thing to keep in mind: the 40106 is a lot of audio for the buck but in reality can't hold a pitch to save its life. Any temperature or current variation--even a slight one--drives the output pitch crazy. Even power cycling the chip changes its pitch for a given RC value.  So it's no substitute for say an ASM VCO.  But for effects and noisemaking, it's just fine.

About the goz-outtas: This is a bit un-Lunetta but I wanted to get the output waveforms 10V P/P or close. So I also incorporated some quad TL072 based buffer boards I have been messing with for a few months. I will try to post more details on my website soon but this is four of the non inverting op amp gain stages you can find on my website fab'd on one PCB.  

I had to go through a few generations for this--the first gen had a bozo mistake with how I laid out the resistors, but what is below worked.  I have already designed Gen3 with a more logical layout for the resistors which you can see are all over the place in GEN2.  this is the world of easy PCB prototyping?

This is basic op amp stuff, but the quad non-inverting board can be used to take four different CMOS type signals and turn them into say +8V Peak to Peak with a 4V DC bias offset.  Since you have to buffer the triangle out of the 40106 I had to do something like this right?




UPDATE.  It makes more sense power supply wise to use inverting stages w bias offset vs. what I have below. The boards will draw much less current!  I have information about a more power efficient board in the BOWAL project and on my website.

"It even does FM": Another interesting thing: it's way easy to add FM to this. Add a diode reverse biased and a 1K resistor in series ahead of the RC that sets pitch and then feed it any audio signal above maybe 2V P/P for um.....interesting results.  I will try to post some bleep-bleep sounds but for me this is hours of fun.

In other words: take this fragment and put it between your audio signal and the FM1, FM2, FM3 etc. inputs you see on the board.  Does it get easier?



Some build photos......

Finished module, still need to do front panel artwork.  

Perfland, easy way to make a few small boards into one big module
OK time tor record.....in case anyone wants to see more here is a zip of the entire design pdf.  if anyone has other ideas about this please comment, I'm always up for seeing what others are doing in 40106 land.  And I will try to add sound samples down the road.  Don't breathe the fumes!

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