[ST]: Fun with Pitch and a Somewhat Original Contribution :D

mtmattan

Hey guys,

Finally built this. Had the design and parts ready for 4 months and the enclosure ready for a month.
Funny how real life tends to get in the way of what's really important ?

Worked first time even! There is a faulty pot I need to replace then will record a demo.

Before I forget, what does it do?
It modulates the pitch of signal with A) A bunch of different waveforms B) With tap tempo C) With a blend control.
What that equates to is a chorus/vibrato pedal with some nifty features.

Quite pleased with it because it's a somewhat original contribution to the endless ocean of guitar pedals.

Here's the ancestor from which the pedal originated - completely redesigned though.

Matt.

Johnny-B

Are you using the ElectricDruid Tapflo microprocessor for waveform generation?

mtmattan

Precisely. Amazing little thing that.
Been trying to optimize the code for frequency modulation as opposed to amplitude modulation.
Ie trying to make some of the waveforms more useable for use in a pitch modulator.
Fortunately aside from the PT2399 delay chip, the audio path remains entirely analogue.
That's the beauty of using an LED/LDR combination ?

Johnny-B

Mattocaster wrote: Precisely. Amazing little thing that.
Been trying to optimize the code for frequency modulation as opposed to amplitude modulation.
Ie trying to make some of the waveforms more useable for use in a pitch modulator.
Fortunately aside from the PT2399 delay chip, the audio path remains entirely analogue.
That's the beauty of using an LED/LDR combination ?

I guess you will need to drive a voltage controlled oscillator (ie V to f converter) with the output of the Tapflo.

mtmattan

Nothing quite as complex as a VCO. From what I've seen, no one has actually developed an analogue VCO that accurately reproduces the sound of a source signal. The Infanem Second Voice uses a similar concept except that it uses Phase Locked Loops instead of a VCO - but although it gets octave effects it's by FAR a clean signal. (Part of its appeal though!)

What it's doing here is using an LDR to vary the Pin 6 or 2 ground resistance of the Pt2399 delay chip with the brightness of the LED to achieve the pitch effect.
As an experiment, try turning the delay/time knob on your delay while playing and you will hear the same pitch modulating effect.
Its a nice alternative to classic analogue chorus pedals (like the EHX Small clone etc) that use BDDs chips driven by a clock frequency.
It's even more elegant in the sense that the LED (digital) and the LDR (analogue) circuits are entirely physically separate. If you look closely there are actually 2 PCBs in the enclosure.

So what that equates to is an analogue tap tempo controlled chorus/vibrato pedal.
Ie to achieve the tap tempo and different wave forms, there is no analogue to digital signal conversion - so the purists remain a bit more at ease.
An LED/LDR combination is by no means novel (even certain phasers use that configuration) but what is novel is using a microchip rather than an LFO to achieve both the tap tempo and waveform generation in a pitch modulating circuit.

mtmattan

Check the vid.
As mentioned, gotta replace the Blend pot as its faulty.
So currently can only get vibrato, no chorus (clean + vibrato).

Matt.

Danny-B

Matt, your pedals are amazing. I found out the other day that you are good friends with my sister, Sophia Basckin.

mtmattan

Oh haha!!
Ya saw her the other night when she was up here in Jhozi.