Blue Box with PWM and waveshaping, need advice

[SonicVI]

I'm compiling some circuit bits into a new pedal and need some advice on ways I could improve performance.
I started by breadboarding the PWM with the LFO from the folkurban circuit snippits page:


I increased the 100uF cap in the LFO to 470uF  for a smoother mod wave and increased the 2.2uF cap to 10uF to slow down the mod rate.  At slow speeds the wave seems a bit lopsided though, for lack of better verbage it's like the wave rises, holds for a bit, then falls, like a trapezoid kinda. Is there a way I could make the LFO be more triangular?

This circuit sounds cool enough by itself,  but then I though why not take advantage of the pulsewave output and put it through octave division. So I put the output through the 4013 section form the MXR Blue Box (http://www.tonepad.com/getFile.asp?id=73). That worked and sounded cool, basically sounds really similar a Blue Box with variable pulse width. The flip flop gets confused though when the LFO is faster and the pulse gets narrow. That's kind of a cool effect, the octave jumps up and down in time with the LFO. Should I maybe drive the 4013 with one of the unused schmitt triggers in the 40106 instead to make the octave more stable?
I also stuck in a 100K pot to blend the outputs from the 40106 and the 4013
.

Then I added after the blend pot output the waveshaping part of this circuit (just the "weird RC" part between the opamps) :


This is where is kinda got iffy. With pot pots at max, basically square wave, it's fine, and with one at max, saw, it's ok, but anywhere in between it seems to lose a lot of volume and high end. Maybe that's just the nature of the "trapezoidal" form?  I didn't add the output buffer because the output of the PWM is so great as it is I didn't think it'd be necessary.   

The last thing was a 100K pot for a master volume control and a cap for a bit of low pass filtering to reduce some sizzle.

So, I'm trying to think of some improvements for better results.  I would also like maybe to add a simple octave up circuit in parallel with the division circuit. Any suggestions for something simple that would work ok here?   Finally, I was thinking of trying out the folkurban 9V MS-20 lowpass on the end of everything.  Any suggestions for things to look out for between the circuits or when blending or mixing the outputs from everything?  I have the feeling that I could be doing that better than just a pot.   

Any thought or suggestions would be appreciated. This is really my first attempt at "designing" a new effect by compiling circuit bits.

[oskar]

This circuit sounds cool enough by itself,  but then I though why not take advantage of the pulsewave output and put it through octave division. So I put the output through the 4013 section form the MXR Blue Box (http://www.tonepad.com/getFile.asp?id=73). That worked and sounded cool, basically sounds really similar a Blue Box with variable pulse width.

My way of thinking.   

If you divide the frequency of a pulse that is asymetric ( not 50/50 duty cycle ) then you will get a perfect squarewave one octave below...
If you listen you will notice that the variable pulse width is good only for the original pulse and not for whatever comes out of the 4013!

The flip flop gets confused though when the LFO is faster and the pulse gets narrow. That's kind of a cool effect, the octave jumps up and down in time with the LFO. Should I maybe drive the 4013 with one of the unused schmitt triggers in the 40106 instead to make the octave more stable?

Sounds like an excellent idea only two little wires away!

Also I definitely think that you should make another 40106 LFO and drive one XOR input with it and the other XOR input with the guitar pulse. (perhaps from before the pulsewidthshaper or after buffering it ). The output from the XOR is ringmodulated... love it!

oskar

[Processaurus]

Some similar ideas to the ones you're working on: http://www.diystompboxes.com/smfforum/index.php?topic=43469.0

Getting a triangular LFO:
http://www.diystompboxes.com/smfforum/index.php?topic=54460.msg422045#msg422045

The flip flop gets confused though when the LFO is faster and the pulse gets narrow. That's kind of a cool effect, the octave jumps up and down in time with the LFO. Should I maybe drive the 4013 with one of the unused schmitt triggers in the 40106 instead to make the octave more stable?

Yes.  Definitely try putting the PWM after the octave division (you could just drive the 4013 with a fixed pulse width from your PWM, then come back out of the 4013 and then use some more of the schmitt trigger inverters to do the real variable PWM), once it gets divided the original guitar octave pulse width has no effect since the flip flop just counts pulses, regardless of how long they are on/off. 

The octave jumping sounds really cool, that's one of my favorite classic synth sounds.  I'm trying to figure out if there is a way to do that with the existing lfo (taking the square wave off the inverter output) and the 4013, if not, it would be elementary with a 4053 spdt analog switch, to switch between the guitar pulse and octave down pulse.

[oskar]

Some similar ideas to the ones you're working on: http://www.diystompboxes.com/smfforum/index.php?topic=43469.0

Wonderful     

[SonicVI]

Also I definitely think that you should make another 40106 LFO and drive one XOR input with it and the other XOR input with the guitar pulse. (perhaps from before the pulsewidthshaper or after buffering it ). The output from the XOR is ringmodulated... love it!

oskar

Forgive my ignorance, but could you explain XOR?  Is that another term for the flip-flop?   

[SonicVI]

Some similar ideas to the ones you're working on: http://www.diystompboxes.com/smfforum/index.php?topic=43469.0

Getting a triangular LFO:
http://www.diystompboxes.com/smfforum/index.php?topic=54460.msg422045#msg422045

The flip flop gets confused though when the LFO is faster and the pulse gets narrow. That's kind of a cool effect, the octave jumps up and down in time with the LFO. Should I maybe drive the 4013 with one of the unused schmitt triggers in the 40106 instead to make the octave more stable?

Yes.  Definitely try putting the PWM after the octave division (you could just drive the 4013 with a fixed pulse width from your PWM, then come back out of the 4013 and then use some more of the schmitt trigger inverters to do the real variable PWM), once it gets divided the original guitar octave pulse width has no effect since the flip flop just counts pulses, regardless of how long they are on/off. 

Thanks for the links. I hadn't seen that before. Awesome stuff.    Ok, so I increased the 33K resistor in the LFO to around 150K and it definitely improved the slow sweep but as you said it reduces the amplitude as you increase speed. I'm thinking the solution may be a dual ganged pot to to increase and decrease that 33K as speed is reduced and increased respectively. Maybe a dual 500 pot with one element reduced with a resistor in parallel. 

That makes since to do the division first so you're modulating the pulse width of the divided signal rather vice versa, which has no real effect.    I'll give it try.  I need a bigger breadboard!

My blend control isn't working too well. I get full volume when it's all guitar or all divided signal but it's weak in between. I think maybe using the separate schmitt triggers would improve this as well. What do you think?

[oskar]

Also I definitely think that you should make another 40106 LFO and drive one XOR input with it and the other XOR input with the guitar pulse. (perhaps from before the pulsewidthshaper or after buffering it ). The output from the XOR is ringmodulated... love it!

oskar

Forgive my ignorance, but could you explain XOR?  Is that another term for the flip-flop?   

No, it's a logic gate like the AND, OR...

http://en.wikipedia.org/wiki/Logic_gate

On the same page where you found the schemo's above there is a digital octave above that use this gate.

oskar

[SonicVI]

I'm thinking of maybe trying this for an octave up, the ring mod from the ARP Odyssey, with both inputs driven by another 1/6 of the 40106, or from the outputs of the 4013 and PWM.   

[SonicVI]

.

[oskar]

For octave up!



The arp thing won't do octave-up. A real ringmodulator can do frequency doubling but this one won't... I've tried it... ( not meaning it isn't possible just because I failed at it though...        and the one I failed with was a pure XOR ringmodulator á la KORG MS-20 )

The circuit above only uses two gates leaving you one for ringmodulation and one for... more ringmodulation... more is better than less.
Try all of them and report back sooner than later...   

[SonicVI]

I'm going to try a few.  I'll report sucesses or failures.      I may be getting a little more ambitious than my current abilities will allow, especially when it comes time to move from the breadboard, but this is my tentative plan:
The heart will still be the PWM circuit with the LFO, I'll have 2 40106's so that I'll have enough inverters for everything,  but instead of using just the one 4013 I think I'm going to use either one 4013 and one 4017, or 3 4017's, in parallel, dividing by 2, 3, and 4, and possibly a 4011 or 4070 based ring mod also in parallel with the carrier input being switchable between the guitar signal to get an octave up or a simple square wave audio range oscillator with it's own LFO, both based on inverters from the second 40106. I haven't found which ring mod to use that will work yet, but I'm hopeful I will find it. If not then I'll just use an octave up and delete the osc and lfo.  All four divided/multiplied signals will go to a mixer so each one will have it's own volume control, then that will be routed either before or after the PWM, into which the straight guitar signal will be sent, so I can have the option of pulse width modulating the divided signals or not. Then all the outs will go to the simple wave shaper.  I'll add any buffering or filtering as is called for. I'll probably add just a simple tone control before the output. I'll also have some on/off, shape, and speed range switches for the LFO(s).   I think I'll leave off the resonant lowpass filter and just run the output through my Micro Synthesizer.

[Celadine]

Nice work! 

FYI, the XOR (or the ARP NAND thing) gates don't really do any ring modulation.  They sometimes can make clangy sounds and some distortion that sounds like ring modulation.  The MS-20/ARP avatar only called it ring modulation for marketing.  Not critisizing anyone, just letting you know. 

If you want 'real' ring mod, the lm1496 is pretty cheap, and there are a few designs around for it.

[SonicVI]

Nice work! 

FYI, the XOR (or the ARP NAND thing) gates don't really do any ring modulation.  They sometimes can make clangy sounds and some distortion that sounds like ring modulation.  The MS-20/ARP avatar only called it ring modulation for marketing.  Not critisizing anyone, just letting you know. 

If you want 'real' ring mod, the lm1496 is pretty cheap, and there are a few designs around for it.

That's what I've been looking at now. I've been searching old threads to try to find some ideas.  The data sheet for the 1496 even has a schematic for a balanced modulator.