Vibrato build log

[cloudscapes]

Figure I'd log down my progress on a vibrato I'm building. Nothing as exciting as my 14-second delay of a year ago, but it's something. 

I've built vibratos before, all based around a pt2399 delay line modulated by a microcontroller. Last one I built was 5 years ago though, and I figured now would be a good time to freshen the design up, and combine new ideas I've learnt since then.

I'll still be using the pt2399 for the delay line, I liked the sound of it with some aggressive filters (for a dark vibrato). I don't want something clean. So most of the work will be with the microcontroller. lfo will be made using a 32bit pic, insetad of an 8bit avr like in my last vibrato. It'll allow me complex lfo morphing/blending! A list of features:

- Several lfo shapes, the regular sine, triangle, square and ramp, with the addition of weirder shapes, all blendable between each-other (using a pot, rather than switches).

- Pinching and 'bulging' of lfo waveforms. So I can tweak a sine wave to have sharp tops and bulgy bottoms, or the opposite.



- Wet/dry mix, for chorus.

- A shaping mode that allows you to draw out an lfo shape with a knob.

- Randomness blending to any lfo shape via dedicated knob.

- Depth and speed controls, of course. Perhaps speed modulation.

- Tap tempo

- Silent relay bypass.



Because I want fancy lfo shapes, I wanted a way to translate drawings of shapes into data that can be used by my microcontroller. I didn't find software that did what I wanted, so I wrote my own (in game maker, of all things). It opens a PNG with my waveform, and a few seconds later outputs a data array ready to be pasted in my microcontroller code.

[cloudscapes]

Some code running on the microcontroller! Right now no vibrato circuitry. It's just the pic32 on a breadboard hooked up to a few pots, leds and passives. I'll do the actual vibrato part next weekend, probably!

Here I'm playing around with the pinch feature, pinching and bulging a sine wave, then the rest of the video I'm cycling through other waveforms as well as pinching.

[thermionix]

That Rigol is giving me flashbacks to my last job.

[Kipper4]

Cool .
Does it do heartbeat?

[cloudscapes]

Cool .
Does it do heartbeat?

By mixing the ramp-down wave with the pinch, I got something close. I haven't finished making all the basic shapes either. I have 6 right now, want to have at least 10. Plus the variance random and pinch adds.

[cloudscapes]

just a loop (guitar ebow whatever) feeding into the vibrato, and playing around with the knobs. I haven't even done random blending or half the other shapes yet.

[nocentelli]

Amazing.

[cloudscapes]

Thanks!

It can do subtle too, just that the video was long enough.

Since PCBs take a few weeks to manufacturer/arrive, priority is to get the hardware done faster. Then I can write in the features/tweaks that only require programming while I wait.

[cloudscapes]

I've more-or-less gotten the hardware part done. The vibrato sounds good, even though I haven't done all the waveform tweaking features in software yet! Just had to make sure the microcontroller could recieve soft-stomp input, control the bypass relay, modulate leds, etc. So I can start on the PCB layout, and finish some of the software-only features while I wait the 3 weeks for it.

I use relay bypass for my designs now. Unfortunately it was impossible to once again get it totally click-less. Narrow the click down to just the relay contacts bouncing. There wasn't enough bias DC offset on the input/output caps (+pulldowns) to cause a pop/click (3-6mv offset), and it wasn't the relay popping the rails/ground either, I tested it with its own isolated power supply to eliminate that possibility. Tried 3 good quality relays, picked the one that I felt clicked the least, and I'll go with that. It's not loud enough to bother me, but it might bother others who use it unfortunately. At least it doesn't click at all when no sound/instrument is being played.

[notnews32]

This is amazing.. thank you for sharing this with us.

I'm envious of your microcontroller abilities. I've been playing around lately with pitch shifting ideas myself.. the amazing thing about guitar effects is that even when it seems like every effect has been done over and over and that there can't be any new territory for guitar to expand into, there IS always something new and exciting just a few solder joints away if you have imagination and are persistent.

I can't wait to hear what becomes of this, I'll be keeping my ear to the ground near you for sure! Best of luck.

[cloudscapes]

There's plenty of new kinds of ideas out there, waiting to be boxed up! Or even many of them may not be new in the form of software/VSTs, or in the modular synth world, but new in a pedal format. Not everyone wants or can play with a laptop on their pedalboard, or a modular system.

[slacker]

That sounds great, some really interesting stuff going on. The picture to wavetable converter sounds like a handy tool, much nicer than using spreadsheets which I've done in the past.

[disto]

cloudscapes this sounds amazing. I am intrigued to know how you are controlling the pt2399. Presumably you are using a control voltage, to pin 6 I guess. Or are you using a opto-coupler? Do you mind sharing some details?

I found a great article here about the PT2399 http://www.diyaudiocircuits.com/tutorials/pt2399-digital-delay-analog-echo/ which lead me to this article www.homebuilthardware.com/index.php/projects/pt239x-delay/ which talked about supplying a control voltage to the PT2399.

I saw a youtube video of your original pt2399 vibrato and it sounded really interesting. Can't wait to see what this evolves into. Keep up the great work.

[cloudscapes]

I'm control-voltaging the pt2399 with a couple npn transistors. used that over optocouplers because the consistency is a bit better between parts. I'm doing the voltage control more like this, with tweaks:

http://www.valvewizard.co.uk/jennygreenteethschem.jpg

I'll post the finished PCB layout later, which I've already ordered. don't have a finished schematic at the moment though, since I usually go breadboard straight to layout software.

[disto]

Thanks cloudscapes I'll have a look at that. Might be just what I'm look for.

[cloudscapes]

layout

[disto]

cloudscapes it looks like the 10uF caps just below the 7805 is the wrong way round. Unless I'm reading it wrong, the positive leg is going to ground.

[cloudscapes]

cloudscapes it looks like the 10uF caps just below the 7805 is the wrong way round. Unless I'm reading it wrong, the positive leg is going to ground.

Good catch, thanks!
I'll just flip it around when populating the board, ignoring the marking. I just have to remember...

[cloudscapes]

Took a break from DIY, back-ish now. Got the PCBs, populated one and threw it in an unfinished box. Workies! Quite amazing really, for the last few years I had kind of gotten used to things not working when I first plugged them in, requiring hours/days of probing and bodges. Gut shot for the curious.



Couple things. That one yellow cap near the right side, decided to socket it. Some PT2399s are noisier than others. So that there cap is a simple low pass filter, making it a wee bit darker. Was 0.022uf, now a 0.047. I think if I make batches of it, I'll keep that cap socketed so that users can experiment with dark/noise.

Using a new 3v latching relay for bypass, TXS2-L-3V, works great! Tiny!

I need to finish firmware features. Tap-tempo hasn't been done yet (because it's boring, honestly). More fun is adding a custom shape thing, where you hold down the tap switch for half a second then it enters record-shape-knob-movement-as-custom-wave mode!

One thing I'm currently trying to decide. The shape pot is how I switch between the several available waveshapes, and it blends between each of them. I still haven't decided on how many I should use, or where they are. Currently using 5, sine, tri, square, ramp up and a weird pinch bubble I made. Want to have more like 7. But a pot has like 290-300 degrees range. Worried if I add too many, it'll be slightly trickier to fine-tweak a setting. I'll experiment with 7. Maybe it won't matter since it's just an LFO, and not actual audio.

The other dilemma is the order of the wave types. Sine blended into triangle is more intuitive, and falls more in line with synths, but sine->square->tri produces really interesting in-betweens!

[cloudscapes]

nevermind, I'm an idiot