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User’s Manual
Note from the Builder
Thank you for choosing Tone King’s Ironman II precision power attenuator. The
Ironman II is a new generation of power attenuator, with a sophisticated design that
preserves the tone and feel of your amplifier quite well, while reducing the volume level
at the speakers.
There are two important components to the Ironman II design that make it unique and
particularly effective - the tuned reactive load and the transformer coupled power
division circuitry.
The idea was that the load seen by the amplifier should always have the appropriate
complex impedance curve so that it responds as it does to a real speaker load. A real
speaker load varies greatly with frequency. For example, the impedance of a typical "8
ohm" speaker may rise to 60 ohms or more at its resonant frequency (usually around
60-80Hz), and then rise again to many tens of ohms at high frequencies. An amplifier
responds a lot differently when driving a complex load like this, compared to a simple
resistive load (as is used in most attenuators). We developed the Ironman II's reactive
load circuit by matching the results of impedance curve measurements we ran on an
actual speaker in typical cabinet. The resulting design was then tweaked through
empirical methods, in order to create a load circuit that is most effective at preserving
the tone and feel of your amplifier.
The second part of the equation is the circuitry that divides the power from your
amplifier between the speaker and the load. In other attenuators, this is often done
with a resistor ladder. There are two problems with this approach - first, the resistor
ladder itself can become part of the load, which means that the amplifier sees a simple
resistive load. Second, in dividing the power this way, a voltage divider is effectively
formed between the dividing network and the speaker. Since the speaker has a
complex impedance that varies with frequency, the result is that the frequency response
at the speaker is altered, usually dulling the top end and muddying the sound.
The scheme we chose involves 100% transformer coupling, using a set of custom
transformers, so that the connection between the amplifier to load, and between the
amplifier to speaker, is purely transformer coupled at every step of the attenuation dial.
This is an expensive and elaborate design (each step of the dial requires its own tap on
one of the custom transformers), but is significantly more effective at preserving the
tone and feel of your amplifier more than other methods.
In this new Iron Man II design, we added an analog speaker cabinet simulation for DI
purposes (balanced XLR)
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Included is a level switch (line and microphone inputs), an
option to select between speaker center or edge micing and a ground-lift to avoid
ground loops in conjunction with other equipment.
Summary of Contents for Ironman II
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