Electronic Audio Experiments Halberd User manual

Technical Manual
Halberd
Version 2
September 17, 2021
John W Snyder

1 Introduction
Thank you for purchasing the Electronic Audio Experiments Halberd. This manual is an
in-depth guide for properly understanding and enjoying your pedal.
The Halberd is a transistor-based overdrive engineered for i) high dynamic range, ii)
superior note clarity, and iii) musical shaping of an instrument’s frequency response into an
overdriven amplifier. The Halberd tends towards a jagged treble response, which is a result
of my affinity for the tones of 90s post hardcore bands and (somehow also) Neil Young. I
would hesitate to call it a transparent drive, because it does not automatically 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 Depth
control shapes the gain in a tactile fashion, allowing the user to morph their transients from
sharp and immediate to fuzzy and blown out.
The signal path of the Halberd is comprised of discrete transistor gain stages. Inte-
grated circuits, such as the op amps found in our Longsword drive (and countless other
pedals), consist of many transistors working in tandem—so many that the quirks of indi-
vidual devices are smoothed over, and the function of a particular amplifier block becomes
abstracted into arithmetic. Filters and gain stages may be configured in a straightforward
and predictable manner via external components. In contrast, when working with single
transistors the bias, gain, and frequency response all interact in a dynamic and nonlinear
fashion. Of course, no approach is inherently superior. But I feel that the unique qualities
of the Halberd come from embracing the quirks and nonlinearities of discrete 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,
originally released in summer 2018. The concept was transformed and refined through sev-
eral 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 would like to thank Bryan from Soursound and Matt from Electrofoods Ultd.
for their critical ears, sage circuit advice, and encouragement.
In 2021 we decided to develop Halberd V2 in a smaller form factor. While doing so, we
successfully designed out the hard-to-source new old stock germanium transistor, reduced
the power consumption by over 60%, and added a new Voice toggle to provide expanded
tonal options.
I am extremely proud of this pedal and hope you enjoy it. Thanks for reading!
-John Snyder, EAE
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2 Product Changelog
Version 2
Released in August 2021
• New mechanical form factor; size reduced from BB-type enclosure to 125B-type enclo-
sure.
• NOS germanium transistor no longer used. Circuitry updated accordingly to preserve
tonal characteristics1.
• Current draw reduced to 50mA when engaged (previously ∼180mA in V1)
• 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.
1The germanium transistor in V1 required careful selection as well as an extra calibration procedure during
assembly. When replacing it with a silicon transistor we optimized the filtering and clipping response to closely
resemble the original design and subtly improve where possible. The end result is, in fact, slightly smoother
sounding than V1 at low gain.
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3 Power and I/O
To power your Halberd, use a standard, reliable 9VDC center-negative supply with a 2.1mm
barrel tip. The Halberd has a current draw of 50mA when active. We suggest the use of
an isolated power supply when using the Halberd in a signal chain with several pedals.
Recommended brands include Truetone™, Voodoo Lab™, Cioks™, etc.
The power input is protected against over-voltage, under-voltage, and reverse polarity
conditions. The unit will not turn on if an incorrect power supply is used. Please note that
all Electronic Audio Experiments products do not use batteries.
"Warning: Halberd V1 units have a current draw of 180mA and will be damaged
if a supply other than 9V is used.
Use standard shielded 1/4” cables to patch the Halberd into a pedal chain. The input
jack is on the top right and the output jack is on the top left.
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4 Controls
Pre Overall input gain level. Turn clockwise
to increase overall signal gain. Lower
settings impart light compression, then
increasing amounts of clipping up to a
medium overdrive, depending on pickup
output and the Depth setting.
Depth Adjustable low frequency shelving fil-
ter at the input. Turn clockwise to in-
crease the bass content and produce a
round, fuzzy drive tone. Turn counter-
clockwise to cut bass for a tighter or
more clangy sound. Very interactive
with the setting of the Pre control.
Tone Ajustable high shelf cut at the out-
put. Turn clockwise to open up high fre-
quencies, or turn counterclockwise for a
darker tone. When below about 9:00, it
can produce an effective bass boost in
conjunction with higher Post settings.
Post Overall output level. Note that ex-
tremely loud signals are possible here.
This control is buffered for full trans-
parency at all settings.
Voice This dramatically alters the voicing of
the overdriven signal. There are three
switch positions, Clang (up), Standard
(middle), and Deep (down). Note: avail-
able on V2 only.
The Halberd has soft-touch electronic switch-
ing with buffered bypass. When the Halberd
is disengaged, your signal passes through a
high-headroom, class A JFET buffer to pre-
serve its integrity over long cable runs.
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5 Detailed Operating Instructions
When using the Halberd for the first time, we recommend using a clean amplifier and no
other pedals. Begin by turning the Pre, Tone, and Depth knobs to noon and the Post knob
fully CCW. Move the Voice toggle to its middle position. Activate the pedal by pressing the
footswitch, and then slowly turn up the Post knob until the desired volume level is reached.
You should hear a medium-gain overdrive tone. Adjust the Pre control to your preferred
level of gain. The Tone knob can be used to tame harsher harmonics at higher gain settings,
or bring in chime at lower gain settings.
At this point you can adjust the Depth. You will likely observe that it is highly interactive
with the gain from the Pre knob. The unique transistor gain stages experience clipping dif-
ferently across the frequency spectrum. Bass frequencies become fuzzy with slower “blown
out” transients, whereas midrange and high frequencies take on a glassy sheen of upper
harmonics. The Depth control therefore has a huge impact on the headroom, compression,
and clipping waveform. Turn it up for a fuzzy tone, or turn it down for a more chimey tone.
The Voice toggle is also interactive with the Depth and Pre settings. It has three posi-
tions: the center position is identical in voicing to a V1 Halberd. There is a gentle midrange
emphasis and a moderate amount of gain. The up position (Clang) adds a significant high
mid boost, to achieve more aggressive sounds than what the Depth control offers on its
own. Similarly, the down position (Deep) adds a full range gain boost that can become very
heavily saturated at high Depth settings.
The Tone knob spans a wide range, and its ideal position will depend on the other control
settings. When the Depth control is turned counterclockwise, the Tone 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 Depth control, one may perceive an effective reduction in
high frequencies. The Tone control may then be increased to compensate.
Finally, the Post control is capable of an enormous level of output. At higher Pre settings
the output signal can exceed +25dBu peak, which is more than enough to overwhelm the
input stage of an amplifier. Use judiciously.
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Document Revision History
Version Changes
2 Release for Halberd V2
1 Release for Halberd V1
0 Draft Copy
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