Section-4: PRODUCT OVERVIEW
ICON is a musical instrument preamplifier, comprised of six independent tube-based tone generation
sections, each with its own input jack and output jack, and its own dedicated tube gain stages. This makes
ICON unique in the world of musical instrument electronics. Multiple players can use ICON at the same
time.
ICON is based on widely used preamplifier topologies which have individually become “icons” of tone at
least in the context of the complete integrated amplifier products in which they are commonly found. London
Power has made minor changes to some of these to enhance the usefulness of the preamp portion on its own.
Ten small-signal dual-triodes create the clean and high-gain sounds. These are of the standard pin-out (9A),
and can be any of 12AT7, 12AU7, 12AY7, 12AX7, 12BH7, 12BZ7, 12DF7, 12DM7, 12DT7, 12DW7,
5751, 5814, 5963, 5965, 6201, 6211, 6414, 6679, 6680, 6681, 6829, 6913, 7025, 7247, 7318, 7728, 7729,
7730, ECC-81, ECC-82, ECC-83, or any equivalents or variants. It is generally the case that types of the
12A_7 or ECC-8_ will be used, as these are what the circuit is optimised for. Others in the list above,
particularly those with dissimilar sections, can provide interesting “in-between” gain levels compared to the
identical-section types. Any tube to be considered must have a 12V heater between pins 4 and 5.
All tubes are external, accessible on the rear panel, and do not require a bias adjustment: just “plug-and-
play”. To replace a tube, turn the power -OFF, gently extract the tube by rocking and pulling, then gently
insert the new tube, being sure to line up the gap in the pin circle on the tube and socket. When the tube is
properly seated, turn power-ON. Each tube contains two triode gain sections, so swapping in different types
changes two gain stages within the preamp. “Mu” is the maximum voltage gain of the tube, listed as
follows:
12AU7, ECC-81: mu=20
12AY7: mu=50
12AT7, ECC-82: mu=70
12AX7, ECC83: mu=100
Preamp tubes require about 100-hours of use to be “broken-in”. Their infant tone is brighter and harsher
than their later tone, at which point, the tube is on its “tone plateau” and its performance does not change
perceptibly over the rest of its life (50+ years).
Each channel of ICON can be used on its own and as many channels can be used simultaneously as
required. Channels can also be chained together in series for extra gain; however, this may lead to excess
noise or even instability depending on which channels are used and in what order, the choice of tubes fitted,
and the control settings. Channels can be mixed together without risk of phase cancellation as due care has
been given to phase coherence, i.e. all channels are unity-phase (non-inverting).
ICON can be used with any type of electrified musical instrument, including guitar, bass, keyboard, or any
acoustic instrument fitted with a dynamic or piezo-electric pickup. The preamp can be part of the primary
tone generation path or be used to re-amplify recorded signals. It is hoped that the versatility of ICON
encourages creative explorations by the studio personnel and by the player.
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ICON Operating Manual Pg.9 © 2019 Kevin O’Connor, London Power
