harmonizer posted

[Joe Davisson]

The name's dumb, but...
http://www.analogalchemy.com/pedals/shocktave.html

The pedal has it's own "organ" that plays along with your guitar at a different frequency. The analog frequency sensor tracks without delay, but is somewhat dependent on how good the preamp can square-up the input signal without adding too much else. It goofs up sometimes, but in those cases the frequency produced seems to "snap" to the next closest harmonic, so not all is lost. Light picking produces errors which cause this effect, for example.

It likes to hang out in the octave zone, at least as shown. Work needs to be done on the frequency sensor to allow more prominent non-octave frequencies to be generated. I'm pretty happy with it as-is, though. Have fun!

-Joe

[ExpAnonColin]

Hooray!  Very cool!  I think I will build one for my theremin...

-Colin

[Samuel]

"is somewhat dependent on how good the preamp can square-up the input signal without adding too much else"

So. Wow. Does the frequency sensor require a square wave-ish i.e. distorted input?

The next couple free hours i have will be in front of a breadboard. Very intriguing, Joe.

[zachary vex]

so you power up your divider through the base of Q3?  i don't get it.  did you leave off the Vcc for the divider?

[brett]

I just LOVE it when people do weird stuff with transistors.  Just check out what Q3 is doing. :shock:
thanks heaps Joe

[smoguzbenjamin]

Sweet. What about somehow splicing the harmonizer sound from the input and having that playing together with you dry guitar signal... think of the possibilities

[Gringo]

Well, there goes another right to the queue!

Thanks Joe, and good luck with your vulcan power amp

[Joe Davisson]

so you power up your divider through the base of Q3? i don't get it. did you leave off the Vcc for the divider?

The 1uF cap charges. The diode breaks over with each signal peak, activating Q3. The oscillator drains the 1uF cap. If the input frequency is higher, the oscillator doesn't have as much time to drain the cap, so the effective voltage is higher. This raises the frequency of the oscillator. Since the oscillator is tuned too low to keep up, it tries to do every other one, producing the octave-down.

So the oscillator kinda acts like a divider, although it's really generating a new signal of it's own. If there's no input, it just powers down. Hope that makes more sense.

So. Wow. Does the frequency sensor require a square wave-ish i.e. distorted input?

Not really, just needs to peak with the input frequency. The single gain stage only distorts slightly. I mixed in this dirty signal, but like Ben said you could take the mix from the input cap instead, maybe taking the output from the opposite oscillator transistor to preserve phase? (not sure if it's right anyway...) Just thought of this, might turn the Q2's 1k emitter resistor into a gain control, for those high-output pickups.

-Joe

[R.G.]

You might help the synch up a bit if you derived spikes from the input signal and fed them to one of the oscillator bases. This tends to kick the next cycle off if it's near starting. Should make for some good partial-lock scenarios.

[Joe Davisson]

Just made these quick & dirty samples:

http://www.analogalchemy.com/pedals/shock1.mp3
http://www.analogalchemy.com/pedals/shock2.mp3

-Joe

[Samuel]

Second link isn't working...But the first one sounds very very cool!

[RDV]

Joe:

Does the 1uF have to be an electrolytic? Or can I use a film?

Thanks!

RDV

[Marcos - Munky]

Cool, Joe. You give more work for us. Now it's time to build one of this harmonizer. I think it will be my next build. I will try to draw a PCB for it later.

[Joe Davisson]

fixed the sample.

the 1uf can be anything

thanks for the tip RG

[mattv]

Wow.. Thanks Joe!

[smoguzbenjamin]

Whatabout chords? Does it behave nicely with chords, or 'power chords'?

[Doug H]

Sounds great, Joe.  Nice and simple too.

It would be cool to add a control for selecting intervals other than octaves too.

Good stuff!

Doug

[rocket]

as zach, i can't quite understand how the circuit works, especially around q3.
is there no dc at the emitter?

[EdJ]

Wow!Would be nice to have one again,thanks very much!
Ed

[Paul Marossy]

Very interesting circuit, once again.  

EDIT: I listened to the sound clip when I got home. Sounds very cool.
I have gotten similar tones using my Jawari in conjunction with a high gain pedal. But, I think this might sound better than that combination, or at least different...