Inverters form three phase VCO

synthmonger

http://www.edn.com/contents/images/80201di.pdf

I came across this circuit about a year ago and I'm 99% I built it using a 4069 and not 74HC04. Right now I'm having trouble getting it working using a 4069UB chip and I am not totally sure I am wiring it correctly and I don't have any 74HC04s on hand to test it out.

Can anyone tell me how this thing should be wired? I am not sure why there is a circle on the third gate and one floating on the transistor. I tried connecting them but doesn't do squat. I am also wondering why there is a 5V battery connected the way it is in the schematic.

Anywhos I think everyone could find this circuit useful. Would make a neat addition to the fonik's version of the resonators eh? Cool

Tim Servo · Posted: Thu Jul 17, 2008 4:00 pm Post subject: Inverters form three phase VCO

Hey Synth,

Harry Bissell, a regular on SDIY, took the same 2001 EDN design and came up with his own improved version (complete with exponential voltage control!)...

http://www.edn.com/article/CA6298270.html

I'd say either build Harry's version, or at least study it to gain more insight on the earlier design and why it isn't working.

Looks like a fun circuit. Maybe I'll add this to my "must build" list (item #7,352).

Tim (an irregular on SDIY) Servo

synthmonger · Posted: Thu Jul 17, 2008 5:10 pm Post subject:

What the beans?! Hah I searched for nearly an hour on this schematic and I couldn't find any info on it. Can't believe google failed me ;C

Thanks Tim!

synthmonger · Posted: Thu Jul 17, 2008 9:07 pm Post subject:

Ohhh VDD! Duh now I get it.

Scott Stites · Posted: Mon Jul 21, 2008 12:47 am Post subject:

Thanks Servo!! How did I miss this Bissell-gem?

Scott Stites · Posted: Mon Jul 21, 2008 12:48 am Post subject:

Anndd.....I know he realizes he's enabling circuits based on....BBDs. Wink

Hmmm.....

loss1234 · Posted: Tue Jul 22, 2008 5:23 am Post subject:

wow is this really a CV controlled LFO showing up in edn?

(the transistor does make it CV controlled right?)

thanks!

Tim Servo · Posted: Tue Jul 22, 2008 6:41 pm Post subject: Inverters form three phase VCO

Hey Scott,

Yes, I just happened to remember Harry doing a tri-phase LFO, so I just did a search for Bissell and tri-phase and hit it. My Google-fu was strong that day.

Loss, yes it does look like a pretty cool VCLFO. Harry has done a few other synth circuits for EDN, including an envelope follower. The search is done as an excercise for the reader. Wink

I'd have to wire this one up to have any hope of figuring it out. The expo converter looks about as simple as it gets (a little like the ARP expo, where the input summing node is the base of one transistor), but what I don't get is how the voltage control actually works. My guess would be we tweak the 4069's supply in some way (some form of starvation?), but why does the CV go to a couple of gates, and why are the outputs of those gates left unconnected? Is there some weird substrate potential biasing kind of sort of thing happening? Help me, Obi-Wan...

The output summation to get three waves 120° out is pretty neat, and you could probably play with that a bit to get some other phases. All in all, a very interesting circuit. I'd also be interested to see what sort of range it has. And yeah, it probably would work pretty well for a triple BBD delay :-0

Tim (a few degrees out of phase) Servo

synthmonger · Posted: Tue Jul 22, 2008 11:08 pm Post subject:

Using the parts suggested in the schematic gives too limited of a frequency range. I upped the caps to 2.2NF to get a huge frequency range but at lower frequencies the peak to peak is boringly low.

I added a faux sync like Osamu did http://www5b.biglobe.ne.jp/~houshu/synth/VcoMos0212.GIF but with the diode facing the gate instead of the cap which worked out great.

The sine wave isn't 100% symmetrical but it does sound awesome. You can get a full 7 octaves using 2n2 caps.

In the sound file I swept the frequency from lowest to highest and back again. After that I added a simple 40106 pulse wave to the sync input and did some knob twiddling. The sync cuts the signal when the vco is set 25% of the way. Kinda whacky, I think the breadboard I'm using is going kaput which may be the cause of that.

FYI it recorded super low for some reason so I bumped up the amplitude in cool edit which added a buncha noise, disregard it! Razz

Anywhos all this really needs is a greater voltage swing.

Anyone try using this expo trick on other chips? I'm going to test out a 40106 in the same manner and see how it works. I should probably try out a 4049 too...

loss1234 · Posted: Wed Jul 23, 2008 3:25 am Post subject:

WOW WOW WOW

that is the most promising bit of CMOS wizardry i have heard in a long time. a real expo controlled cmos oscillator. cheap and easy.

i need to make 10.

i also want to know if this trick will work on others.

thanks for the memories

loss1234 · Posted: Wed Jul 23, 2008 5:17 pm Post subject:

if i dont care about the three phases...do i need the opamps? maybe just one? or none? (does the differential amp only contribute to the phase or to the whole operation??)

with 6 oamps and all the diodes and caps, its a bit bigger than i thought. still a great circuit though. hope i have the right zener!

can i use a tl072? these are questions i will answer tomorrow for myself but i wondered if anyone else had had luck with them.

thanks as always

loss1234 · Posted: Wed Jul 23, 2008 5:25 pm Post subject:

synth monger
????
did you try the expo with other cmos chips

i was wondering if the expo ONLY worked because of something ELSE going on in the circuit?

id love to figure out how to control a 40106 with an expo!!

loss1234 · Posted: Wed Jul 23, 2008 5:28 pm Post subject:

one more question:

i cant tell. does this circuit reverse the polraity of the vss and vdd inputs??

it looks like he has VOLTAGE coming in on 7 which is grnd
if this is essential to the expo trick i want to know that i am not going to fry my other cmos chips doing it. (i think the 40106 can handle that for sure though)

thanks

loss1234 · Posted: Wed Jul 23, 2008 5:39 pm Post subject:

LAST POST I PROMISE ON THIS

i only have 6v zeners or 5v or 9.1v
can i stick 2 together?
can i just use a 6v?
or can i ditch and just risk frying my chip?

darn. i have 20v schottkys.

nobody uses 10v zeners around here. so i dont stock em.

boo

fluxmonkey · Joined: Jun 24, 2005 Posts: 708 Location: cleve

loss1234 · Posted: Wed Jul 23, 2008 6:54 pm Post subject:

but doesnt that take WAY more circuitry?? dont get me wrong thats a great circuit. but thats more of a precision circuit. this is great for a ten minute build.

I GOT THIS TO WORK WITH JUST A CD40106 and the 2 transistor part. (as well as the weird supply connections)

NO OPAMPS at all. i think an opamp buffer or some kind of offset would get rid of the ONLY problem i running into (which isnt the giant sweep range or the fact that i can now LFO AND EXPO control a 50 cent chip like nothing) which is a weird HUMMING at super low and high frequencys

it could be because i used a 9 volt zener. or because i used a weak 12volt dual supply. i think if i could get help adjusting this for 12volts i would be in heaven with cv controlled chips.

!!!!

thanks all

widdly · Posted: Wed Jul 23, 2008 7:13 pm Post subject:

Rene's 4069 is much less circuitry if you leave of the PWM at the bottom right.

Interesting that this works with 40106 also.

loss1234 · Posted: Wed Jul 23, 2008 7:37 pm Post subject:

THE THREE PHASE PART HAS NOT been tested with the 40106. JUST the expo converter with the weird power supply setup. but the expo control is what mainly interests me. three phase is cool but wide sweep so easy on a 40106 is really useful.

can anyone tell me why i might be getting bad noise and hum on the very top and bottom of the sweep range??

thanks

synthmonger · Posted: Wed Jul 23, 2008 9:52 pm Post subject:

It sorta worked with a 40106 when I tried it out, the range was really limited, maybe half an octave? I'd like to try it with a 4049 but I haven't the time.

I remember an old forest m. schematic I posted a while back where the 4049 was configured to have square and triangle phase differences, unfortunately the picture I posted has been deleted. I assume if everything was setup the same with in that schematic (with the addition of the expo control to pin 7 ) it can become voltage controlled. I am too busy right now to mess with that ;x

widdly · Posted: Wed Jul 23, 2008 10:38 pm Post subject:

loss1234 · Posted: Thu Jul 24, 2008 5:54 am Post subject:

sure. but really all you need to do is look at the schematic that was made for the 4069 and cut out EVERYTHING except the expo converter and the stuff going to pins 14 and 7.

i might not be able to make a schematic for awhile.

by the way...unlike synth monger i was getting many many octaves.

i wired up the 40106 just like you would normally wire it up for a single 40106 inverter oscillator. (with a pot and a cap to ground)

Synth monger when you tried it with the 40106 what did YOU take from the 4069 schematic? i was getting crazy sweep range. i will post a sample.

thanks all

loss1234 · Posted: Thu Jul 24, 2008 8:13 am Post subject: schematic

here you go

i did the best i could removing any areas that would print dark.
(never done this before)
i dont have a scanner so....

anyway, i could really use help readjusting my resistor values for +/- 12volts. i am not sure if they should be bigger values or smaller to compensate.

i looked at in on a scope and the DC offset seems weird. (not referenced to ground? i dont know the correct terminology so if anyone else could test this (synth monger)

i got a huge range with a 474 cap and a good lfo range with a 4.7 or 1uf cap. (on pin 1)

thats it

maybe an opamp buffer would help

thanks

(or the right zener!!)

expo cmos final paper.jpg

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synthmonger · Posted: Thu Jul 24, 2008 5:28 pm Post subject:

What kind of waveform is at the output? Typical square like you would get?

The only difference I had was that it was powered from +/-9volt coming from a max1044 chip. I have it setup on a tiny breadboard for testing my pedals.

I found an interesting way of using it each gate. So you can get 6 expo controlled vco's. The output waveform is a superrrrrr narrow pulse wave which I think could be used for bugbrands bitcrusher and certainly for a plethora of other circuits requiring a narrow pulse wave. I'm using the other gates to widen the pulse and dividers.

Right now I have it set up to control 1 of the gates as an oscillator and the others as pulse width modulators for the main divided vco. Sending the pulse wave forms through an integrator can give it a variable waveshape, which in turn gives it simultaneous pulse width modulation and cv waveshaping.

I'll post the schematic and my pcb of it when I have the two versions finished.

Also loss1234 I know you were talking about using a transistor as a vc resistor and I've found using this expo source to control an mpf102(sp?) with expo source works pretty well.

P.S. I'm running on a couple hours of sleep so I apologize in advance for spelling and grammar errors Cool

loss1234 · Posted: Thu Jul 24, 2008 7:08 pm Post subject:

synthmonger-all that confused me was that you were saying with a 40106 you werent getting more than an octave or so.

"I've found using this expo source to control an mpf102(sp?) with expo source works pretty well. "

what do you mean? you used an expo to control another expo?

thanks

synthmonger · Posted: Thu Jul 24, 2008 9:42 pm Post subject:

Oh woops! A bit redundant there. Like I said in my P.S. I was running on little sleep so please excuse the grammatical errors.

Anywhos, I was using the expo source to control a fet transistor mpf102 to act as a vc resistor...at least I think that's how it worked! I didn't test it out on anything else but a 40106. Basically I replaced a resistor with the S and D legs of the MPF102. The G leg was sent to the output of the expo source and it worked out so-so.

Anywhos here's something that'll keep you busy.

easypeasyvco.jpg

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