The Slacktave, CMOS octave down fun

[loss1234]

tried the diode trick you recommended and it works great. i figure it was user error that was giving me problems with single supply!

btw, this makes a great front end for a 4046

thanks

[Boogdish]

I just finished breadboarding this and it is fun, fun, fun.  I'm doing this, the nyquist aliaser and an echobase before I go back to school.  Summer of Slacker.

[Boogdish]

I modded my slacktave today.  I built the last half of the "simple square wave shaper" presented on Tim Escobido's page into the output of the pedal.  here's a schematic:

and here are some sound clips.
http://www.aronnelson.com/DIYFiles/up/slacktave_demo.mp3

This in my opinion really brings out a lot of life in the pedal.  You lose some of the volume, so I'm thinking about putting a small booster/buffer between the output of the mod and the volume control. This was also really easy to do, I built it point to point using the back of one of the pots for ground and a little bit of shrink wire to keep things tidy.  I'd post a picture of that, but our old camera broke and we haven't gotten a new one yet.

Thanks to Slacker, Escobido and Bobby Beausoleil (who wrote the article Escobido got his idea from).

[slacker]

Very cool, I'll have to try that out. If you need some extra volume from the pedal try removing the diodes in the feedback loop of the last opamp or replace them with LEDs that should give a decent volume boost.

[mongo]

Ohhhhhhhh  we need a PCB layout for this!!!

[rnfr]

this thing sounds great.  really like boog's mod.   

and anything by bobby beausoleil is going to have some REAL mojo!

[earthtonesaudio]

Does anyone know if you can use more than one of the 4024's outputs simultaneously?  Like a volume control from pin 11, and a separate volume control from pin 12, going into the output mixer section... Would that work?

[slacker]

Yeah that would work fine.

[frequencycentral]

Hi Ian, I'm breadboarding the Slacktave. I don't have all the resistor values, so I'm going for closest match I have. I'm getting good fun with the low E and A strings, although the notes cut off rather abruptly. The other strings do nothing. I'm using humbuckers. The opamp package I'm using is a RC4136 quad (741 type) opamp. The resistor values I'm using are 2M2, 1K, 15K, 47K, 100K, 4K7. I've replaced the 120K on the input of the 4024 with a 0.1uf cap, which helps a bit. Do you think my problem is the resistor values? I know to expect some glitch..........

RC4136 http://www.synthdiy.com/files/2006/4136-rca.pdf

[slacker]

That's a bit odd. The resistor subs should be fine, the weird values in the original were just because that's what I had, mostly the dregs of a resistor value pack. I don't know anything about the opamp you're using but I can't imagine that can be the problem.

I'd try and see where the signal is getting lost. Are you getting a strong square wave on the output of the third opamp stage or is the signal already weak at that point?

[earthtonesaudio]

I modded my slacktave today.  I built the last half of the "simple square wave shaper" presented on Tim Escobido's page into the output of the pedal.  here's a schematic:

and here are some sound clips.
http://www.aronnelson.com/DIYFiles/up/slacktave_demo.mp3

This in my opinion really brings out a lot of life in the pedal.  You lose some of the volume, so I'm thinking about putting a small booster/buffer between the output of the mod and the volume control. This was also really easy to do, I built it point to point using the back of one of the pots for ground and a little bit of shrink wire to keep things tidy.  I'd post a picture of that, but our old camera broke and we haven't gotten a new one yet.

Thanks to Slacker, Escobido and Bobby Beausoleil (who wrote the article Escobido got his idea from).

Does anyone know a way to get triangle, saw, and square out of this using a single potentiometer?  I can only see how to get two of three...

[frequencycentral]

I posted a "theoretical" waveshaper in that other Slacktave thread, haven't tried it yet (ie. it might be a pile of crap!), but it's on the list:

http://www.diystompboxes.com/smfforum/index.php?topic=76695.0

Or there's this:

http://www.diystompboxes.com/smfforum/index.php?topic=77235

[earthtonesaudio]

I was originally thinking to put a SSWSMS (simple square wave shaper made simpler) on each octave's output, but that could potentially be a LOT of knobs, so reducing it down to one would be nice.  If you made the two 1M resistors into two halves of a 2M pot, and brought the signal in through the wiper, as you turned the wiper, you'd get falling saw-triangle-rising saw.  On the other hand, if you made the two resistors fixed and put a variable resistor between D1 and D2, you could get triangle at max resistance, square at min. 

Then I had the thought that rising and falling sawtooth waves probably sound about the same, so it would be really handy if you could have a 1-knob control that went square-saw-triangle.  I think you could do it with a center-tapped pot, but that's somewhat of an odd item, and it'd probably be easier to develop an active version at that point.

Now I'm thinking maybe you wouldn't need the SSWSMS on every octave...

[earthtonesaudio]

Alright, I think I figured out a way to get square/sawtooth/triangle from one potentiometer. 

Signal comes in, splits to the two antiparallel diodes as usual, then each diode goes to one end of a potentiometer.  The cap is attached to the wiper, and the signal output is taken from there also.  Here's the twist: one diode is a zener, with a threshold voltage that is lower than the peak square wave input voltage (so if you run the CD4024 from 5V, use a zener rated at less than 5V, such as a 1n522x).

At the non-zener end of the pot's rotation, the cap charges fast and discharges slow, giving a sawtooth waveform. 
As you turn toward the zener side, the discharge is still slow-ish but the charge becomes slower: triangle
Keep turning and you'll charge and discharge primarily through the zener, so at this point the waveform is mostly square.

[earthtonesaudio]

So I'm thinking you could use all 4 xor gates from a 4070/4077 to get 4 octaves up, then put that into the 4024 to get +3, +2, +1, 0, -1, -2, -3 octave square waves, put the single-pot waveshaper on each one, plus a dry blend.  So that's... 15 knobs.     I'm thinking some of those should be internal trims.

[frequencycentral]

So I'm thinking you could use all 4 xor gates from a 4070/4077 to get 4 octaves up, then put that into the 4024 to get +3, +2, +1, 0, -1, -2, -3 octave square waves, put the single-pot waveshaper on each one, plus a dry blend.  So that's... 15 knobs.     I'm thinking some of those should be internal trims.

I'm listenin' ! But 15 knobs! 

I wanna see a schematic..........! ;¬)

[earthtonesaudio]

Still learning Eagle, but this should convey the important bits:


(Rightclick and select "view image" if it's too big)

All the floating parts that "point down" should go to ground.  Like I said, still learning... 

Also, the "waveshape" and "level" controls should be repeated for the other 6 Q outputs of the 4024.

[Cliff Schecht]

Earthtones, go check out the library called "Supply1" and "Supply2", I think you'll find all of your power and grounding needs . Also on any of your parts with power pins, you have to right click the part and go to "invoke". Ditto for any parts with more than one device onboard (like the hex inverter your using, if you delete one by mistake then you'd have to right-click and invoke the deleted gate number).

[earthtonesaudio]

Thanks Cliff, that helps a lot!

[slacker]

If you're going down the multiply up route, you could try the waveshaper from the PICsynth http://picsynth.000space.com/.
I'm not sure how successful the upper octaves will be though, I think the pulse width might get too narrow to hear. It would probably still work to drive a divider though.
I have another idea along these lines using a CD4046 to multiply the signal up about 8 or 16 times then divide it back down. In theory you would then have enough outputs to make a digital sine wave, or triangle at different octaves. From there you can get saws and squares. You could even go really crazy and make a vastly simplified version of Ian Fritz's DoubleDeka VCO, where you could actually draw the waveform you want.
It will probably have to wait until the winter though, I'm pretty busy with stuff most of the summer.