saw straight out of a 4046 bodge

mike page · Joined: Sep 26, 2016 Posts: 134 Location: norwich, uk

If you set a simple 4046 vco (like the one on hackaday) but put two capacitors in series for the timing cap, then measure the junction between them you have a good solid rising saw!

Try it out!

PHOBoS · Posted: Mon Nov 28, 2016 6:57 am Post subject:

nice, I never tried capacitors but you can do it with diodes:

mike page · Joined: Sep 26, 2016 Posts: 134 Location: norwich, uk

Ah cool! I wasnt planning on putting a buffer on my VCO in. Would you recommend it? Also (sorry if this is a silly question but) what does this do in tracker mode? Do you send a squared up audio source in and it latches to the pitch? Oh and what does the xor out do?!

Cheeerzzz

Cfish · Joined: Feb 24, 2016 Posts: 477 Location: Indiana

Nice. mike. Just tried it.

I'm going on to try the Schematic PhoBos posted too.

Can anyone point me at the reason for using u1a as a ground reference that way? Don't think I have ever seen that done before.

PHOBoS · Posted: Mon Nov 28, 2016 6:49 pm Post subject:

mike page · Joined: Sep 26, 2016 Posts: 134 Location: norwich, uk

Awesome, what alot of fun crazy crap on one chip!
Thanks so much for the thorough run down really helpful.
I was just planning on summing a freq/offset pot and CV source through diode or resistor mixing.

Now if only there was a fool proof way of turning that saw into a triangle!

Cfish · Joined: Feb 24, 2016 Posts: 477 Location: Indiana

I have not tried this one, but it is on here. Saw to triangle converter

http://electro-music.com/forum/topic-30667.html

mike page · Joined: Sep 26, 2016 Posts: 134 Location: norwich, uk

Ah cheers, I tried one of those and couldnt get it to work. I think im going to make digital stepped triangles instead and squish them with a capacitor.

Cfish · Joined: Feb 24, 2016 Posts: 477 Location: Indiana

I'm just a hack, trying to get a better grip on this.

Till now I have stayed mostly in the analog realm.

Would love to see what you come up with.

gabbagabi · Posted: Wed Dec 14, 2016 3:43 am Post subject:

hello mike,
i guess u have powered up your 4046 with +12 or +15V, so the saw is sawing only in the positiv region.
The Waveshapers are build for sawing saws that are crossing the zero line.

anyway the thread reminds me on something from the inventory, see annex

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JovianPyx · Posted: Wed Dec 14, 2016 6:49 am Post subject:

zloth · Joined: Nov 18, 2016 Posts: 12 Location: Augsburg, Bayern

Hello all, 1st post.
Been meaning to ask about the 4046, would it work if I put a chain of resistors between the positive voltage and the VCO so I could "play" it in a way similar to a stylophone?

Cynosure · Posted: Tue Dec 20, 2016 6:21 pm Post subject:

How flat is this saw shape? Does it remain flat at low frequencies? Is it the same amplitude at high frequencies?

Could you post some scope shots at ~60Hz, ~440Hz, ~1000Hz, 2000Hz?

PHOBoS · Posted: Tue Dec 20, 2016 6:30 pm Post subject:

zloth · Joined: Nov 18, 2016 Posts: 12 Location: Augsburg, Bayern

Thanks for the quick reply!
Yes, I later realised I would need a resistor to GND as effectively what I'm doing is making a "stepped starve" control, so instead of having one lug of a pot going to GND I would need an equivalent.
Another manual control for a 4046 I had thought of was a R/2R with one or more inputs controlled by momentary switches. Would this even work?
Talking of which, has anyone tried using more unusual types of input clock, such as Shift Register or even 7-Segment Driver, to create polyrhythms for a DAC?
Sorry for all the questions, still quite new to all this, I'm very much a traditional synth/sequencer person (still use a Korg M1 Laughing

)looking for something to inject a little delicious "live" chaos but a more exciting than a plain vanilla APC, although I have had fun with various 4093 configurations.
Thanks again.

J-chot · Joined: Jan 20, 2014 Posts: 44 Location: Decatur AL

Hey, if I was running this off of a bipolar 12 volt supply, would I omit the U1a circuit and just tie 10 and 5 of the lm324 to ground?

Sorry to resurrect a dead thread, but it beats making a new one.

PHOBoS · Posted: Sat Mar 28, 2020 3:55 am Post subject:

yes, BUT the 4046 will likely not survive a bipolar 12V supply. It might depend on the manufacturer but the datasheet I have here
specifies a maximum voltage of 20V, so you could use a bipolar 9V supply. Also connect the level pot to the (fake) GND as I did here.
This way the level pot doesn't affect the frequency when nothing is connected to the CV input.

J-chot · Joined: Jan 20, 2014 Posts: 44 Location: Decatur AL

Can I run the 4046 off of + 12 ground, but also use the CV circuitry/opamp as bipolar?

JovianPyx · Posted: Tue Mar 31, 2020 5:30 am Post subject:

The schematic PHOBoS posted looks like it is set up to work with single supply. U1a is a virtual ground stabilizer. That circuit should work from +12 v. The + symbol on the schematic goes to +12 and the - symbol goes to PSU ground or zero volts.

PHOBoS · Posted: Tue Mar 31, 2020 6:46 am Post subject:

J-chot · Joined: Jan 20, 2014 Posts: 44 Location: Decatur AL

Ok, I've built it to spec, no negative rails
Everything on it works EXCEPT for my CV response. I get barely any change in pitch until I feed it close to 10 volts, then the 1.6v on pin 9 of the cd4046 jumps to 5.

Pin 1 is 5.58 (it's getting 11.4 so that sounds pretty good)
Pin 7 is 1.16 no matter how I twist the knobs.

Feeding it 0 to 4.6 volts with a sequencer.

PHOBoS · Posted: Mon Apr 06, 2020 4:14 am Post subject:

That sounds like one of the opamps is functioning as a comparator which means there is a problem with one of the feedback resistors.
What is the voltage range you get out of the last opamp if you turn the offset pot and have no CV connected ?

Did you measure the voltage on pin 7 with an oscilloscope ?

J-chot · Joined: Jan 20, 2014 Posts: 44 Location: Decatur AL

Ok, I THOUGHT I had found the problem, but it's not really improved much. I had connected the offset to ground instead of positive. Late night bonehead wiring error. I've checked the chip connections like, 80 times, feedback resistors just as much.....

CV response range (input) is NOW approximately from 3.27 to 7.89 I get a little more than an octave. (Like 1 step more)

Now with nothing plugged in, Pin 7 reads from 4.42 to 10 when I twist offset full range
The pitch now seems too high regardless. Flipping the "low to high" now puts it in the dog whistle territory.

I'm using a POS digital multi meter for these readings. ...seems a bit more accurate than my 1973 telequipment d61

PHOBoS · Posted: Tue Apr 07, 2020 1:29 am Post subject:

are you using this version ?
You should be able to get close to 0V. 10V could be correct as the LM324 won't go completely to the positive supply
although I think it might be able to go a little bit higher. Also looking back at the schematic I'd replace the 47K resistor
connected to the offset pot with 100K or maybe even larger.

Maybe I have some time later to see what the range is I get here, should be more than an octave I think. And yes,
the high range can get pretty high, maybe replace the 22nF with 47nF or whatever you like.

btw I thought you meant pin 7 of the 4046 hence why asked about the oscilloscope.
I was already wondering why you were interested in that voltage Laughing

J-chot · Joined: Jan 20, 2014 Posts: 44 Location: Decatur AL

I tried attaching that wire to both ground and the reference voltage. It seem to function better attached to ground.

I really appreciate all your help, I've been racking my brain figuring out what I did wrong. I suck really bad at the math part. In fact, I don't usually do that part.