The Slacktave, CMOS octave down fun

[slacker]

Ladies and gentlemen allow me to present the Slacktave, an all new octave down pedal I've been working on for a while. It uses a CD4024 ripple counter to generate 1 or 2 octaves down that can be used on their own or mixed with a nasty comparator fuzz for a wide range of fuzzy synth like textures.

Here's the schematic
 
http://www.eskimo.plus.com/fxstuff/slacktave.png

and some samples, all played around the 5th and 12th frets
one octave down
two octaves down
fuzz
fuzz plus 1 octave mix
fuzz plus 2 octave mix

The basic idea of using the 4024 came from Ken Stone's sub-oscillator and I've tried a few different ways of hooking it up to a guitar to get decent tracking, this is the first version that I thought was worth sharing. It uses a modified version of the fundamental extractor from the Electrax guitar synth that Stephen Giles posted a while ago to drive a comparator that's hooked up to the clock pin of the 4024. The divide by 2 and 4 outputs are then used to give the octaves and these can be mixed with the comparator output. If my maths is correct the mix pot also acts as a variable highpass filter so as the octave is blended in more low end is rolled off the fuzz side which helps bring out the octave.
It tracks pretty well between about the 3rd and 17th frets and works best on the middle 4 strings. As with most of the these things you get the best results using the neck pickup with the tone rolled down, this gives the most stable octave down. However if you use the bridge pickup you can get an octave jumping effect.
This is still on the breadboard so if anyone's got any ideas for improvements I'd be happy to hear them. Any comments on how it sounds compared to the other octave downs out there would also be cool.

[petemoore]

  Tha's working good !
  Nice and synthy, good tracking ! cool

[birt]

cool sound. very very synthy!

[slacker]

thanks I'm thinking of using it as the input stage for a guitar synth type project, so synthy sounding is good.

[jpm83]

That's really cool. Are you planning to do a vero layout for thisone?

[jmusser]

That came out well, and is simple to boot! It is quite a bit more sythy than the Shoctave, which is good or bad depending on what you like. Some people like it to sound like a bass, which takes a horrible amount of filtering. I like both type of tones. It sounded like it was tracking pretty well too. I wasn't hearing a bunch of what I call "sonic bumblebee" where it finds the note initially, but then hunts around for it and warbles up and down. That gets annoying after awhile. Good job!

[slacker]

Thanks, I did think about trying to filter the octaves to clean them up a bit and make it sound more bass like but I like the fact that it's synthy. It could probably be used a building block to make a more natural sounding pedal though.
The fundamental extractor really improves the tracking by removing a lot of the high frequencies giving a cleaner signal to the comparator. The comparator then puts out a decent constant voltage square wave, which suits the 4024. The earlier versions did suffer with the "sonic bumblebee" effect, which is why I never posted them.

That's really cool. Are you planning to do a vero layout for thisone?

thanks. I've done a vero layout it just needs labelling, once it's done I'll post it.

[ambulancevoice]

fuzz octave 2 sounds a shit load like a blue box! 

[birt]

this is actually the guitar sound that is closest to what i've been looking for for some time now.

i want something that is capable of "Gap Band - you dropped a bomb on me" upt to the fantastic sound of "Chemical Brothers - my elastic eye". if it can only do the last one it's fine by me :p

maybe the last one is possible by taking only fast samples of the guitar signal and generate octave down sounds with those. i'm definatly gonna try that if i have the time.

[markusw]

Very cool!! 

What are you using for the comparator? Is it an opamp?
Since it's still on breadboard it would probably be worth changing it to a LM311 because it's faster. The 4024 might prefer this. Once I tried to feed the output of a LM311 into a 4013 divider an it worked very nicely.
Maybe also check for offset voltage at the +ve in of the comparator. It might be worth a try to AC couple the +ve input with a e.g. 100n cap and a 100k to Vref.

Markus
 

[slacker]

Thanks for the advice

The comparator is just an opamp, which seems to work fine and means the circuit only uses a quad opamp and the 4024. Having said that, adding an LM311 would free up an opamp, which could be used to do something else, like an octave up!
I might try AC coupling the input of the comparator and see if that improves anything.

[slacker]

If anyone fancies having a go at building this here's a vero layout.

http://www.eskimo.plus.com/fxstuff/slacktaveboard.jpg

I haven't built it yet so it's unverified and as the design is still somewhat experimental things could change.
By the way apologies for the odd resistor values, I've got one of those resistor multipacks and I've used up most of the common values and I'm trying to use up the rest of the values rather than buying any more.
If you haven't got the exact resistor values just use whatever you've got that's within 10% or so, after all it's only a fuzz 
I don't know if it matters but the actual code on my CD4024 is CD4024BE

[gez]

Clever use of the 4024.  Gets round the problem of picky flip-flop clock inputs (especially chips made by ST, which I've always had to buffer to get them to work).

[calculating_infinity]

Damn slacker, sounds sick!  This is definately on my to build list.  Thanks for sharing!  Now I need to get me a 4024.

[slacker]

Clever use of the 4024. 

Cheers, to be honest it seemed so simple that I was quite surprised that no one had done it already.
Listening to the soundclips I think the 4ms Nocto Loco is based on the same idea, but using the rest of the dividers as well. I did try using those and you can get some intersting effects but I thought a basic octave down pedal might get more interest.

Damn slacker, sounds sick!  This is definately on my to build list.  Thanks for sharing!  Now I need to get me a 4024.

Thanks, it shouldn't be too hard to find a CD4024, I don't think smallbear has them, but any of the usual electronics suppliers should.

[gez]

Clever use of the 4024. 

Cheers, to be honest it seemed so simple that I was quite surprised that no one had done it already.

I was slapping my forehead when I saw it.  Sometimes the obvious is staring us in the face, just needs someone to point it out to us.  Thanks! 

[krachbox]

4ms did.

http://www.4mspedals.com/nocto.php

[slacker]

yeah, I already mentioned that I discovered the nocto loco while browsing one day after I'd been playing around with my idea for a while. As soon as I heard it and saw what it did I guessed it was using a similar idea and thought someone was bound to figure it out or they'd release a schematic, then it would look like I'd copied it.

[krachbox]

Yes, but it will take some time before they (4ms) will release it as a kit. I know because I asked.

[slacker]

If you look at the data sheet for the 4024 you should be able to figure out some of the nocto's sounds