Circuit testing and debugging

Everything fired up first go. The channel boards contain the PLL, VCO, waveshaper, ringmod, VCA, lock indicator and various related electronics. There are two identical channel boards, capable of operating independently from each other, but really designed with cross-modulation in mind. Each board is controlled from a 8-bit parallel data bus. Many features are jumperable the board is laid out for easy experimentation with features. There are so many possible configurations! Testing everything as a complete unit is difficult due to the sheer complexity of the PCB interconnect wiring and front panel control stuff. So I've been breaking it down into smaller parts, "divide and conquer".

One of the two 'channels' near completion.

Digital control board, PIC goes in the empty socket.

Two identical 'channel' boards.

Analog Harmonizer/Octaver PCBs

Lots of progress has been made during the last 6 months.

Design finalized, circuit prototyped, PCBs designed and manufactured,

components fitted, circuit tested and debugged (partly still in progress) ..

Some of the pre amp and fundamental extraction circuitry is built by hand on perfboard or breadboards. The remaining boards, 3 double-sided and 1 single-sided, are all done. 

Making your own boards like this is hardly worth it considering how relatively easy it is to have a board house make the PCBs for you. However, buying this many boards from a fab house would be pretty expensive, especially when I probably won't bother with more than one unit. So in this case, a single run, prototype through hole. 

Some photos of the etching process;

Sample of the PCB designs.

Developed PCB.

Etching in a etching tank.

Preview of the result.

All PCBs etched.

State of Guitar-Synthy-Monstrosity -affairs

Input stage, compressor, filtering & fundamental extractor.

Overview: Input stage bottom left.
Input/output -thingy top left.
Channel #1 top right. Channel #2 bottom right.

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..

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.

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.