Electronic Audio Experiments Halberd Technical manual

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Technical Document
Halberd Manual
Version 0 [Draft Copy]
Last Revised: 23-Oct-19
John Snyder

INTRODUCTION
Thank you for purchasing the Electronic Audio Experiments Halberd. This manual is an
in-depth guide for properly understanding and enjoying your pedal. Below is a bit of
context. If you would like to skip ahead to how the pedal works, begin reading at the
Operation section on the next page.
The Halberd is a transistor-based overdrive engineered for 1) high dynamic range, 2)
superior note clarity, and 3) shaping an instrument’s frequency response to an
overdriven amplifier. The Halberd has a tendency towards a ragged treble response,
which is a result of my affinity for the tones of 90s post hardcore bands and Neil Young.
I would hesitate to call it a transparent drive, because it does not inherently preserve the
tone of one’s signal chain. It is more like a chameleon, responding in a unique way to
different pickups, string gauges, picking attack, even chord voicings. The pre-gain bass
control shapes the gain in a tactile fashion, allowing the user to control the compression
and note attack in a fashion not found in other EAE pedals.
At the risk of diving into buzzwords, the Halberd’s signal path is comprised of discrete
transistor gain stages. Integrated circuits, such as the op amps found in the Longsword,
consist of many transistors working in tandem – so many that the function of a particular
circuit block becomes abstracted into basic arithmetic. Filters and gain stages may be
configured in a straightforward and predictable manner via external components. In
contrast, when working with single transistors, bias, gain, and frequency response all
interact in a dynamic and nonlinear fashion. No approach is inherently superior, but I
feel that the unique saturation of the Halberd relies on its careful approach to gain
staging which embraces the quirks and nonlinearities of silicon and germanium
transistors while channeling them into something controllable and decidedly modern.
While the Halberd began as a standalone iteration of the preamp in our Sending delay,
it was radically transformed through several months of intense and occasionally manic
engineering development. The final outcome would never have been possible without
the help of some relentlessly discerning beta testers. In particular, I’d like to thank Bryan
from Soursound and Matt from Electrofoods Ultd. for their critical ears, sage circuit
advice, and encouragement.
I am extremely proud of this pedal and hope you enjoy it. Thanks for reading!
-John Snyder, EAE

OPERATION
Only use a standard, reliable 9VDC center-negative supply with the Halberd (e.g.
Truetone™, Voodoo Labs™, Strymon™, Cioks™, etc). The Halberd has a current draw
of 100mA. Supplies with AC output or a DC voltage greater than 9V will risk damaging
the pedal and voiding the warranty. The Halberd does not use batteries.
The Halberd has soft-touch relay switching with buffered bypass. When the Halberd is
disengaged, your signal passes through a high-headroom class A JFET buffer to
preserve its integrity over long cable runs.
The control knobs are as follows:
•Pre: This sets the overall signal gain. Lower settings impart light compression,
then increasing amounts of clipping up to a medium overdrive, depending on
pickup output and the Low setting.
•Low: This is an adjustable low frequency shelving filter at the input, and is very
interactive with the setting of the Pre control.
•High: This is an adjustable high shelf cut at the output, for taming harsher
frequencies especially at high gain settings with Low cutting bass.
•Post: This sets the overall output level, and is buffered for full transparency at all
signal levels.
The Halberd’s controls are highly interactive. To understand these interactions, one
must first understand the role of the Low control. The unique transistor gain stages
experience clipping differently across the frequency spectrum. Low frequencies become
fuzzy with slower “blown out” transients, whereas midrange and high frequencies take
on a glassy sheen of upper harmonics. The Low control therefore has a huge impact on
the headroom, compression, and clipping waveform.
The High control spans a wide range - where one sets it will depend on the other control
settings. When the Low control is set to cut bass content, the High knob may be turned
down to tame harshness or focus the output into a narrow band of midrange. As more
low frequencies are brought in via the Low control, one may perceive an effective
reduction in high frequencies. The extra range on the High control may then be
increased to compensate.
Finally, the Post control is capable of an enormous level of output – when the Pre
control is turned up the output signal will approach 16Vpp, which is more than enough
to overwhelm any amplifier’s input stage. Use this judiciously.

In conclusion…
The Halberd is a powerful and versatile transistor drive with a deceptively simple set of
controls. Thank you for supporting our design and manufacturing efforts, and we hope
this pedal serves you well for many years to come.
CHANGELOG
Version 1
Original Release
Version 0
Original release – draft copy
www.electronicaudioexperiments.com