Hog guide

Overview

  • Fully analog signal path and control circuits
  • Two voices with triangle, sawtooth, square waveshapes
  • Sub or noise extra voice
  • Narrow and variable pulse width for voice 1
  • 10 octave precision
  • 5 octaves switch
  • Voice 2 with +/- 1/2 octave and detune
  • 2 selectable LFOs for auto-wah and vibrato
  • Playground with variable modulation paths
  • Custom quick envelope system
  • Glide
  • Variable gate modes (envelope, gate and drone)
  • MIDI upgradable
  • Customizable, hackable, open-source

Inputs & outputs

  • Power source: +12V DC, center positive
  • MIDI in: 3.5 jack, TRS MIDI type A
  • External cutoff: 0-8V CV input to modulate filter cutoff
  • Fat pitch: VCO2 pitch CV, 1V/octave. Use this for paraphonic mode (only available via CV, not MIDI)
  • Gate: 8-12V gate voltage
  • Out: dual-mono line out / headphones out

Connecting a keyboard

In order to play the Hog you need to connect an external keyboard or sequencer. There are two ways to do this.

  1. Hooking up a keyboard that has CV and Gate output like an Arturia Keystep or Korg SQ1. The pitch CV complies the 1V/octave standard, Gate should be 5-12V. The inputs and outputs of Hog are Eurorack compatible.
  2. Alternatively you can connect a controller with standard MIDI output. This can be any keyboard or an audio interface.

Note: if you're connecting both CV & gate and MIDI then CV & gate connections take precedence.

Controls

Global/Voice 1

  • Main volume
  • Main LED: Blinking in MIDI setup mode
  • Shape: Sets the waveshape of the main voice (VCO1). From top to bottom: triangle, sawtooth, square (50% pulse width), square (narrow pulse width), square (pulse width modulated by the speed of LFO2)
  • Octave: Global octave from 0 — +4 octave

Filter

  • Cutoff: Sets the cutoff frequency of the low pass filter
  • Tracking: Adjusts the cutoff frequency based on the note played. Higher notes open the cutoff more.
  • Dirty: Sets the resonance and adjusts the cutoff frequency with the envelope at the same time. Turn it up and use various envelope settings for classic funk sounds.

Fat / Voice 2

  • Fat: Turns on the second voice (VCO2).
  • Turbó: Sets the waveshape of VCO2. From bottom to top: triangle, sawtooth, square (50% pulse width).
  • Detune: Detunes VCO2 with about +/-1 octave
  • Volume: Sets the volume of VCO2. Note that the maximum output of VCO2 is set higher than VCO1 to keep volume headroom.
  • Octave: The octave of VCO2 can be offset related to the main octave. This switch sets the direction of the octave (up/same/down) and the "Amount" switch sets the number of octaves of the offset

Extra voice

  • Extra: Selects between Noise/Off/Sub. The sub oscillator's frequency follows the main oscillator (VCO1)
  • Volume: Sets the volume of the selected extra voice

Envelope

The design of the envelope control allows quickly setting the most common volume shapes. The circuit is fully analog so the attack, release and decay times have nice exponentials which result in natural sound.

  • Soft: Turn on for a slightly slower attack
  • Hold: When on, the note is held until the key is released on the keyboard
  • Ring: If on, the note rings out when the last key is released on the keyboard
  • Time: Sets the release/decay time

Mode & glide

  • Mode: Sets the gate mode. Drone: always on, playing the last note from the keyboard (or C0 if no keyboard is connected) / Gate: uses the gate voltage directly to open the VCA. This is great if you want to use the envelope only for the filter "Dirty" control. / Envelope: uses the Envelope to open the VCA. This is pretty much the default usage.
  • Glide: Turns on portamento between notes.

LFOs

There are two triangle LFOs in the Hog, a top (LFO1) and a bottom one (LFO2). Both can be used to modulate the filter cutoff (auto-wah) and/or the pitch (vibrato).

  • Auto-wah: Selects which LFO should modulate the filter cutoff (LFO1/Off/LFO2)
  • Vibrato: Selects which LFO should modulate the pitch (LFO1/Off/LFO2).
  • Speed: Sets the frequency of the given LFO
  • Amount: Sets how much the given LFO should modulate it's destination

Playground

The Playground area consists of various cross modulations that allows experimental sounds.

  • Playground: Turns on the playground mode (the mid position sends half amount of modulation, for full modulation set it to "up")
  • Switch: Sets the modulation as follows (from top to bottom):
  1. Hard sync: Resets the frequency of VCO2 to the frequency of VCO1. At the same time it modulates the pitch of VCO2 via LFO2. Experiment with detuning VCO2 using the detune knob or the VCO2 octaves as well as with the speed and amount of LFO2.
  2. FM: Modulates the pitch of VCO1 with the output of VCO2. Play around with the frequency, octave and the waveshape of VCO2. You can even turn off VCO2, the modulation remains on.
  3. Filter cutoff AM: Modulates the filter cutoff with the output of VCO2. Try switching VCO2 to the lowest octave and play around with detuning it.
  4. VCA (ring) mod: Modulates the control voltage of VCA with the output of VCO2. Again, experiment with various octaves and detuning of VCO2.

MIDI

The MIDI circuit is the only digital component in the Hog and it's an optional upgrade. The MIDI input is a 3.5 TRS MIDI type A jack.

Setting the MIDI channel

  1. Turn off the Hog
  2. Connect a compatible MIDI keyboard
  3. Hold any two keys on the MIDI keyboard
  4. Turn on the Hog while holding any two keys on the keyboard
  5. Wait about 1 sec after turning on
  6. Release the keys. The main LED should blink (about once every 0.5 sec)
  7. Hold C, D, E, F and G keys on your keyboard to set the MIDI channel according to the following table:
Chan. C D E F G
1 •
2 •
3 • •
4 •
5 • •
6 • •
7 • • •
8 •
9 • •
10 • •
11 • • •
12 • •
13 • • •
14 • • •
15 • • • •
16 •

Once the key(s) are released the main LED blinks fast, signaling that the MIDI channel was saved. Restart the Hog after setting the MIDI channel.

Signal path

Hog is an analog synthesizer following classic subtractive synthesis principles. A pure raw sawtooth is generated in the core oscillators (VCO1 and VCO2) which go through waveshaping that results in various waveforms: normalized sawtooth, squarewave and triangle.

There are two additional sound sources: a sub oscillator, which is generated from the VCO1's output, and a simple whitenoise.

The sound sources are mixed and go to the modified Steiner-Parker diode ladder low pass filter. The output of the filter then goes to an amplifier (VCA) which is controlled by the output of the envelope generator (ADSR).

There are two LFO's in the Hog and you can choose which LFO should modulate the filter and the vibrato. LFO2 is also used to modulate the pulse width of VCO1's square wave.

The Playground section connects input sources with various modulation destinations.

Resources

Schematics and MIDI to CV converter code is available on the Hog Github repo. Feel free to hack it or build it for yourself.