my first "design": an unnnamed synthy octave/distortion waveshaper device

[jaapie]

since this past summer i've been fiddling around with different "synth"-style circuits for guitar, trying to find a happy medium between the relatively simple Guitar --> Square Wave types and more complex designs using PLLs and sync'd VCOs. This is the first circuit I've been able to more or less "finish," and i'm pretty happy with how it turned out. It can do decent "sawtooth" and "trianglish" waveforms as well as the more common square waves, and it follows the dynamics of the guitar pretty faithfully.

The guitar to square converter is lifted more or less part-for-part from Craig Anderton's Rocktave Divider-- it tracks very well, and also includes a VCA tied to the input's envelope, which will come in handy later. The input buffer also feeds a simple phase splitter that i found in this thread:http://www.diystompboxes.com/smfforum/index.php?topic=73802.0 (thanks earthtonesaudio!). An interesting effect I noticed is that, while the collector and emitter signals are 180 degrees out of phase with each other, they both seem to be almost 90 (or 270) degrees out of phase with the input signal (I'm guessing that has to do with the coupling cap before the phase splitter, but I'm not educated enough to really tell)! I don't think they're perfectly in quadrature, but it's close enough for my purposes!

Both the inverted and non-inverted guitar signals are then fed into a 4053 that's clocked from the Rocktave's square wave. Normally, this would simply full-wave rectify the input, but because of the phase difference between the program and control, the result is closer to a curvy sawtooth at twice the guitar's frequency than the series of "humps" that result from "regular" FWR.

Now, here's the cool part: if you take the "sawtooth" wave and add to it a square wave an octave lower (in the correct proportion), you end up with a sawtooth one octave lower! A 4013 divides the square wave (as in the original rocktave), and the "SQR OCT" pot controls the ratio of "unison" and "octave" blended with the original doubled sawtooth. Then it's sent through the other half of the 571, which is configured as a VCA following the input envelope. This ensures that the square wave's amplitude stays proportionate to the guitar's (Otherwise, the chopped guitar would fade out over time while the square waves would keep pumping out full volume until it can no longer track). This way the sound stays somewhat consistent regardless of how loud you play or hold a note. The "GTR/SQR" pot controls (obviously) the mix of chopped guitar and square waves.

The "Voice" switch controls how the guitar signal is chopped up. In one position, the 4053 is controlled by the "unison" octave square wave, which results in the previously mentioned sawtoothy wave. In the center (off) position, the guitar isn't chopped at all and the "clean" guitar is ultimately blended with the square waves. In the lowest position, the switch is clocked from the "not Q" pin of the 4013. The result is tough to describe, but sounds like a "hollower" square wave. When this is mixed with the right proportion of octave-down square wave (from the Q pin), it looks and sounds like a very crude triangle/sine wave.


I know that's a pretty rushed explanation, but I've never had to try describing a circuit I've "designed" before! I'll try and get some decent sound samples when i can, but here's the schematic and some crude scope shots before i leave for work.

Schematic: http://i.imgur.com/kYCYxi7.png

Scope Shots (input on top, output on bottom):

-Sawtooth http://imgur.com/h85vQcv
               http://i.imgur.com/xnaZ0MQ.jpg
(the HF interference is from the CFL in my desk lamp)

- distorted sine/triangle: http://imgur.com/vo2teNG

Any thoughts, comments, corrections or questions would be immensely appreciated!

[jaapie]

Here's a quick video with a couple of different sounds. I'll try and make some better quality samples after work tonight.

[FUZZZZzzzz]

sounds promising! i like how more people are into building weird stuff..gives hope for the future... one day i will have to search the internet for overproduced mainstream music instead of those rare gems
will look out for your better sound clips..

[Jdansti]

Cool!  It even plays Chuck Mangione!  How does it sound with chords?

[slacker]

I like it, looks and sounds very interesting, nice work.

[garcho]

bravo! will breadboard this soon

[jaapie]

It sort of works with chords-- open chords really confuse it, but it will still track power chords and triads if you play them higher up on the neck. You do have to play pretty cleanly for it to really sound good, but i don't feel like it's too restrictive. Like most other octave pedals, it really works best on the higher frets. Some settings seem to track better than others, which is interesting because the parts of the circuit concerning tracking are the same regardless of the knob or switch settings.

[jaapie]

Here are a few more clips. I don't have any kind of recording setup, so I just set my laptop on the floor next to my amp. I've got the tone control rolled back and i'm only using the neck pickup for all three clips.

https://soundcloud.com/jaapie/bass-saw
https://soundcloud.com/jaapie/saw
https://soundcloud.com/jaapie/hollow

[Jdansti]

Sounds great!  (and it plays Herb Alpert!). 

[deadastronaut]

this sounds brilliant...i had your clips going through reverb /delay on my mixer...nice!..

whats it like with tapping/hammering?...i like doing sequencer type stuff on guitar.

this would be cool with envelope filter too....good work man!!!.

edit: stuck an auto filter on it too...awesome is a word i never use, but it is...

[jaapie]

I'm not much of a tapper, but I don't see why it wouldn't work if you can tap pretty cleanly. noise from adjacent strings doesnt seem to screw up the tracking too bad, but it adds a ton of extra intermodulation distortion that may or may not sound good depending on what you like . Hammers and pulloffs work great.

After playing with it some more last night, i'd say it responds similar to a heavy fuzz or distortion until you start blending in the lower octave. It doesn't seem to have any trouble tracking chords or heavy playing until the low octave is more prominent.

I've got an idea for adding a triggered filter using the other half of the 4013 and a few more opamps, but i wanted to get the bare bones hammered out first

[~arph]

Very nice! I'd like to hear it with the octave up sawtooth mixed in  

EDIT: Ow it think it is mixed in 

[glops]

Great first design!