Guitar 'synth' Update

Debugged the new waveshaper circuitry. Works very well using a technique rarely (if ever) seen in audio stuff. Also added a simple ring modulator a'la Korg MS-20 which works very well with the oscillators footswitchable 'note hold'-function.
Some of the 'typical' synth waveforms didn't sound interesting enough and got replaced by  my own weirdo concoctions..

Weirdwaves™

Analog Harmonizer/Octaver

Three out of five 'voices' almost done.

Huge breadboard is huge.

Also; circuit completely redesigned..

Well..

Been busy. Slow going. Not dead yet.

Voltage Controlled Multimode Filter

Commissioned build and still a work in progress. 
Voltage controlled state variable filter with all the bells and whistles.
The filter can be controlled by playing dynamics (envelope follower), voltage controlled LFO/Sample&Hold or manually with a knob/external expression pedal.  Also has a buffered effect loop, wet/dry mix and active volume control.
The envelope follower circuit is pretty complex, at least in the stompbox world..
Frequency specific somewhat log. amplification/attenuation, full wave rectification.. 
Attack and release times are completely independent and non-interactive. The release is linear (as opposed to the 1/2piRC discharge), which means the effective filtering is more effective and any residual 'ripple' or AC components in the envelope voltage is reduced.
However, the change in release time for a given rotation of the release-knob is exponential, which means the response seems natural and useful. 
It has dawned on me that voltage controllable everything is way beneficial.. 

I've spent a lot of time with the sidechain and I'm very proud of the result.

The LFO/Sample&Hold rate can be modulated by the envelope follower. The initial frequency is set with a knob. Another knob then sets the amount of modulation. Set fully CCW, the rate decreases from the initial frequency when picking harder. Set fully CW the rate increases from the initial frequency when picking harder. And set to the 12'oclock position the modulation is disabled. Other controls work in a similar way. Switches < Pots.

All analog. 22 ICs, 28 Transistors.

Filter block diagram

Guitar synth sound sample

Quick and dirty recording of the guitar synth prototype.
The prototype is very sensitive and noisy on the breadboard, so recording is somewhat fiddly. I go through random combinations of interval, octave and waveform. One of the channels is fixed at unity octave.




One channel set at unity interval, unity octave and sawtooth. The other channel is set at squarewave, unity octave. I go through all the intervals.

Analog guitar synth update

My PLL-based harmonizer/octaver/'guitar-synth' has come a long way.
The design goals and circuit has evolved during development.

My current prototype has two separate channels.
Each channel has it's own set of interval, octave and waveform-selectors.

- Available intervals: unison, maj 3rd, perfect 4th, perfect 5th and a major 6th. 
- The octave-selector has six positions: -2, -1, unison, +1, +2, +3. 
- The waveform-selector also has six positions. 
Five waveforms are implemented in the prototype: square, triangle, saw, stepped triangle and stepped saw. I haven't yet fully decided on the last waveform. I'm contemplating pulsewave with adjustable (and/or modulated) pulsewidth.

The synthesized waveforms are sent to a voltage controlled amplifier, which is controlled by the raw guitar signal. This means playing dynamics are retained, and synthesized notes decay naturally, along with the guitar signal. It also eliminates stuttering and glitches at the end of notes.

Each channel also has a 'hold'-function, which when activated holds the note played indefinitely. The held note can be set to follow the guitar amplitude, or remember the amplitude at the time of activation, and stay there. 

Lastly, the two channel outputs and the original guitar signal is sent to a mixer.
A 'balance'-knob sets the relative amplitude of the two channels. And a wet/dry-knob adjusts the amount of raw guitar input vs. synthesized signals.


I've had so much fun playing with the prototype. 
The possible combinations of intervals, octaves and waveforms makes it very versatile.

Next up is some finishing touches and optimization(/minimization..).
The circuit is very complex, with a huge number of components. All of which could be replaced with just a single microcontroller. But what is the fun in that?

Prototype circuit. Lots of chips.

White Octave Fuzz

 

Commisioned Octave Fuzz

High Resolution Photos of the octave fuzz.

The future owner made the graphics. More to come.

Commissioned build

Octave fuzz

Captains log..

Stardate 65437.6

Long time, no updates.
School and miscellaneous annoyances have done a great job of keeping me distracted. I'm currently working on a "analogue" harmonizer/octaver based on a phase locked loop. I'm aiming for a ridiculously high knob-count on this one. Maybe it's time to go modular..

The prototype circuit tracks the guitar surprisingly well and I'm sure tracking will be even better once I implement and test the complete circuit with more efficient signal conditioning.
Two parallel sections with independent controls will allow dual harmonies/octaves. E.g. a perfect 5th, two octaves up and a harmonic 7th, one octave down simultaneously.
I currently get square wave outputs but the plan is to extend the available waveforms. Using example circuits from the CMOS cookbook, I've been able to generate a 'sine' wave. The scope picture shows the raw output from the first trials. After low pass filtering the signal, the blocky stair steps disappear.
No scope photos of the current circuit, you'll have to take my word..

Raw digital 'sine' wave. Looks surprisingly good when LP-filtered.