Halberd

The Halberd by Electronic Audio Experiments is a discrete transistor overdrive circuit designed to provide the greatest possible dynamic range and note clarity. It is a medium-gain device with the harmonic fullness and grind of a much higher-gain pedal, standing apart from both the brazen buzz of op amp distortion and the smooth breakup of JFET amp emulations.

Key Technical Specifications:
- Bypass switching: Silent electronic switching with a Class A JFET buffer
- Input impedance @ 1Khz: 1MΩ
- Output impedance @ 1Khz: <1KΩ
- Power: 9VDC, 2.1mm center negative barrel. The current draw is 50mA. It is recommended to use a regulated, isolated power supply rated for 100 mA minimum. The DC input is protected against reverse polarity and over-voltage up to 24V. The pedal does not accept batteries.

Controls:
- Pre: Sets the overall signal gain, with lower settings imparting light compression and increasing amounts of clipping up to a fuzzy overdrive, depending on the Voice and Depth settings.
- Depth: An adjustable low frequency shelving filter at the input, interactive with the Pre control, affecting low frequencies only.
- Tone: An adjustable high shelf cut at the output, helpful for taming harsher frequencies especially at high gain settings.
- Post: Sets the overall output level, buffered for full transparency at all signal levels.
- Voice: 3 position switch to set the overall drive character:
- Clang (up): Increases gain in the upper midrange for an aggressive sound and a sharp attack.
- Standard (middle): Moderate gain with a gentle mid push; identical to Halberd V1.
- Deep (down): A full range gain boost with woolly saturation and a fuzzy note attack.

Changelog:
- Version 2 (Released in August 2021):
- New mechanical form factor; size reduced from BB-type enclosure to 125B-type enclosure.
- NOS germanium transistor no longer used. Supporting circuitry updated to preserve tonal characteristics.
- Current draw reduced to 50mA when engaged (previously ∼180mA in V1).
- Bypass switching converted to fully electronic CMOS switch.
- Added Voice toggle.
- Added PSU input over-voltage protection.
- Low control renamed to Depth; High control renamed to Tone.

Version 1:
- Original release in Fall 2019. Built in a BB-type enclosure and uses a NOS Germanium transistor in one of its gain stages.

The Halberd is suitable for use with guitar, bass, and synthesizer, and its character comes from over a dozen transistors working in harmony, providing a unique and collaborative response to different instruments and amplifiers.