Teensy FX

• A Teensy 4 based FX unit with Pocket Operator style and playability.
• 12 knobs, 4 buttons each with LED, and 4 LEDs showing automation cycle.
• Combination of filtered reverb, ping pong filtered delay and a noise source, but this is customisable.
• Each knob can be automated (a bit like punch in effects on the Pocket Operators)
• Tap tempo and PO sync
• video series on development and use of the teensy-fx

Hardware

schematic

gerbers

photos

noise performance

Buy the right parts through the links on the kitspace page.

Hardware Resources

Based off the teensy 4 audio board and the teensy beats shield

• teensy 4 audio board schematic https://www.pjrc.com/store/schematic_audio4.png
• SGTL5000 datasheet
• TLC5947 24 channel PWM LED driver
• 4067 multiplexer for the knobs
• pot RK09K1130AP5

Hardware V1: git commit 99c1038

check the git repo out to the hash to make sure everything is in sync.

Errata

• Do not place C16
• Swap LRCLK & BCLK - see pic lrclk-bclk-swap
• 2.2uF ceramics sound as good and are much cheaper than the 1uF acrylics for C8, C9, C14 & C15

Hardware V2: git master

• test points for mic input
• separate regulator for pot 3.3v to reduce noise?
• put leds and buttons below pots for easier viewing and pressing
• leave space on back for rubber feet
• update FP of audio sockets to new FP - audio sockets weren't available in EU, changed to 35RASMT2BHNTRX which has 5 pads but will fit on the same fp
• filter behind pot mux was a mistake. filters must be in front of mux or removed - fixed by removing
• fix LRCLK & BCLK mixup - fixed

Back graphic

• Art by Kipling: http://bit.ly/39Wxc4R. Designed in ContextFree
• 100 x 60mm == 3.94 x 2.36" == 1182 x 708 pix

FW

• each knob controls one of the parameters
• each knob has a number of steps of recordable automation
• knob's leds brightness shows current value of parameter
• record time is based on bpm tap tempo and number of steps (4 bars in control.py)
• buttons are: tap tempo/sync, write, erase and start automation loop from beginning
• press & hold tempo button to switch between tap tempo and PO sync mode
• press write and move a knob to record its movement
• moving a knob without pressing record will wipe the pattern and set it all to the current knob value
• 4 leds on top right show progression through the automation loop

Uploading

• remove modemmanager

• install teensy rules: https://www.pjrc.com/teensy/00-teensy.rules

  sudo cp 49-teensy.rules /etc/udev/rules.d sudo udevadm control --reload-rules sudo udevadm trigger

Then:

make prog

issues

• freeverb noise issue fixed here
  • to fix this you can copy the local effect_freeverb over the one in ~/.platformio
• if delay is not as long as expected (should be seconds), check teensy audio lib is up to date, older versions didn't support teensy4's large memory

Audio patch

made with https://www.pjrc.com/teensy/gui/index.html

Software

control.py is a PyQT program that was developed in order to make an MVP interface that could later be translated to hardware in the form of a PCB.