London Power ICON User manual

ICON
Operating Manual
This manual applies to the London Power model:
“ICON Vacuum-Tube Preamplifier”
musical instrument preamplifier models manufactured from 2019 onward

CONTENTS
1. Warning
2. Wiring Conventions
3. Rack Mounting
4. Connections
5. Overview
6. Preamp Channels
7. System Configuration
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ICON Operating Manual Pg.2 © 2019 Kevin O’Connor, London Power

Section-1: WARNING
RISK OF SHOCK
Electronic amplifiers are powered from the AC mains distribution. High AC voltages and AC currents are
present in the chassis and constitute a risk of shock to the user. Lethal power levels are available from the
mains. Keep hands clear of mains wiring.
HIGH VOLTAGE
Vacuum tube electronic circuits operate at high voltages. High DC voltages are derived from high AC
voltages and both represent a significant shock hazard. Injury and death may result from contact with these
voltages. Keep hands clear of secondary wiring and high-voltage circuitry.
RISK OF SHOCK FROM UNPOWERED EQUIPMENT
Capacitors can store electric charge for very long time periods. Electronic equipment that is unplugged from
the mains and has not been powered for days can still hold enough charge to cause injury or death. Carefully
discharge capacitors using recommended techniques (not shorting) prior to working on the unit. London
Power’s products incorporate automatic discharge circuits so that internal voltages will be reduced to
near-zero within minutes of power-‘off’.
FIRE RISK
Electronic equipment creates heat during operation. Proper air circulation and/or fan cooling will remove
this heat from the unit. Do not obstruct ventilation or otherwise impede heat removal. Do not defeat
protection circuitry or any devices such as fuses, current limiters, temperature monitors, fan servo circuits,
or power reduction circuits.
HOT SURFACES
Electronic devices and chassis containing them can become hot to the touch. Avoid contact of skin with
these surfaces as severe injury can result. Tube envelopes can be 250EC at their hottest point. Soldering iron
temperatures approach 450EC.
SOLDER FUME & MATERIALS HAZARD
Solder used to secure electronic devices contains tin and lead. Solder for electronics use also includes a resin
core to clean the connection while soldering. The resin and solder create fumes that may be hazardous to
health if inhaled. Exhale gently while soldering. A low-speed fan to extract the fumes is recommended.
Ventilation to outside air is preferred. When wet, surface residue on electronic components may be
hazardous to health. Wash hands with cold water and soap after working with electronic components.
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ICON Operating Manual Pg.3 © 2019 Kevin O’Connor, London Power

WARNING (cont’d)
OPERATOR RESPONSIBILITY
The equipment operator must exercise due care in heeding safety advice presented in this manual. The
operator must assure a proper environment in which to use the equipment and a stable surface to support the
equipment. Never leave equipment unattended if powered.
ERRORS AND OMISSIONS
Every effort has been made on the part of the manufacturer to assure that this manual is correct in every
regard. London Power shall not be responsible for loss of income, injury, upset or death or any misuse or
misinterpretation of the content of this text on the part of the reader.
LOUD SOUND DAMAGES HEARING
Exposure to loud sounds over extended periods of time will damage your hearing. The louder the sound, the
shorter the time required to cause temporary or permanent hearing loss. Ringing in ears, numbness or pain,
and feeling “deaf” are all signs that the sound was too loud for the time exposed to it. Health regulating
bodies, such as OSHA, prescribe specific times for given sound pressure levels (SPL) in decibels, to provide
a safety protocol for workers subjected to noisy environments. London Power finds these recommendations
inadequate and recommends much shorter exposure times. Hearing protection should be selected and worn
correctly. However, for a musical environment, the need for hearing protection is a cue that SPL is too high
and other remedies should be explored first to reduce the loudness level. The use of hearing protectors
impairs intelligibility of music and is counter-productive to the creation of an enjoyable Human-Scale music
experience, therefore SPL should be kept below 80dB. Power Scaling assists in this goal by allowing a
“loud sound” to be attained at low-SPL.
Aural compression is invoked at all SPLs and to a greater extent as loudness increases. This is our internal
physiological protection mechanism and it impairs accurate sensation of the sound. Even with hearing
protection in place, aural compression will interfere with our judgement of tone and is a strong motivator to
use lower SPLs. Our judgement of sound is much more accurate at low-SPL than at high-SPL, contrary to
common prejudice.
REFER SERVICE TO QUALIFIED PERSONNEL
This equipment should be serviced only by qualified personnel with technical expertise in dealing with high-
voltage tube circuitry. To assist in serviceability, ICON is built in a U-frame. This allows removal of the top
and bottom covers, providing access to main-board components on one side and solder points on the other.
To access rear panel circuitry, remove the four bolts that secure the rear panel to the sides as well as the two
bolts through the IEC connector and the ground bond screw, then flip the assembly away from the chassis.
To further access the solder side of the tube card, remove the nuts from the jacks and the bolts through the
rear panel into the spacers. Each channel’s control board is accessed by removing the respective control nuts
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ICON Operating Manual Pg.4 © 2019 Kevin O’Connor, London Power

WARNING (cont’d)
WARRANTY & LIMITED LIABILITY
The manufacturer warranties this equipment for Five Years from the date of shipment against defects of
workmanship and electronic component failure, excluding tubes, and reverb delay lines, and excluding
failure caused by abuse or misuse of the product. London Power will not be liable for damage to other
equipment or property caused by negligent use of this product, by misinterpretation of this manual, or by
component failure, or by use of the equipment in inappropriate environs (rain, damp, on unstable surfaces),
by faulty wiring of signal or power paths, by ground faults causing damage to this or other equipment. For
warranty repair, London Power will pay for parts and return shipping. Shipping to us is the responsibility of
the owner. Assure that the unit is packed correctly. Damage during shipping is not covered by warranty.
FUSES
All fuses are internal and are slow-blow types. These are 5x20mm S506-series available world-wide. Fuses
should be replaced with the same type and value.
Mains 200mA x2
Plate 63mA
Heaters 3A
LV 630mA (dual-mains-range units only)
Fuses can blow because the air inside the preamplifier is too hot, due to poor ventilation. If a fuse blows, it
is best to determine the cause of the failure. Replacement with a similar fuse resulting in a second fuse
failure suggests further investigation is required - that something may be damaged in the preamplifier. Most
often a tube replacement is required. Otherwise, refer servicing to a qualified tech.
EXTENDING TUBE LIFE
If there are some channels of ICON that you never or rarely use, remove the related tubes to avoid wearing
them out for no reason, and to save power.
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ICON Operating Manual Pg.5 © 2019 Kevin O’Connor, London Power

Section-2: WIRING CONVENTIONS
The types of interconnections used between audio equipment and between that equipment and the mains are
all very standard. The connection and cable requirements used by London Power products are described
below.
Mains: The AC mains is connected through a male IEC chassis connector using a detachable power cord.
The power cord is a 3-wire type carrying Line, Neutral and Safety Ground between the wall receptacle
and the equipment. The wall-end of this cable has a male connector plug appropriate for the local region; the
equipment endhais a female IEC connector. Replace the AC mains cable if it becomes worn, cut or pinched,
or if the moulded connector ends are cracked.
DO NOT INTERFERE WITH OR DISABLE THE SAFETY GROUND !!
Speakers: Power amplifiers drive loudspeakers via heavy-wire interconnections using a 2-wire cable. This
can be “lamp” or “zip” cord, or a pair of wires inside a sheathing. Loudspeaker current is high, and the wire
must be of sufficiently thick gauge to conduct this current without heating up. For amplifiers up to 100W,
18-gauge wire is sufficient, but thicker wire (#16 or even #14) should be used if the distance between the
power amplifier and the speaker is over 15m (46').
Speaker outputs on London Power equipment <100W use 1/4"-TS female connectors. The tip (T) carries
the signal and the sleeve (S) is ground. Both ends of the cable should be wired identically, using male plug
ends. Connect the speaker end prior to connecting the amp end of the cable - do both with power OFF.
D.I.: “Direct-injection” outputs are typically male XLR jacks. This allows for a 3-wire cable to the
receiving equipment and the connection is most often “balanced”, meaning that the signal itself does not use
a ground connection between the equipment; rather, the signal “floats” so that ground levels become
irrelevant.
At the sending end, London Power uses a male 3-pin XLR connector fed from either a transformer providing
galvanic isolation, or a balanced drive circuit producing symmetrical signals. The receiving end uses a
female 3-pin XLR and either a transformer or a differential amplifier.
The sending end of the D.I. cable is a female 3-pin XLR and the receiving end is a male 3-pin XLR, wired
as follows: pin-1 is the equipment ground; pin-2 is the “hot” in-phase signal; pin-3 is the “cold” out-of-phase
signal. The shield is tied to pin-1.
A less costly interconnection requiring less panel space on both pieces of equipment uses 1/4"-TRS
connectors and a 3-wire cable. The tip (T) is “hot”, ring (R) is “cold”, and sleeve (S) is shield and chassis
ground. Connector sex same as for XLRs above.
NOTE !!! When connecting any output of this unit to a mixer, assure that phantom power is OFF.
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ICON Operating Manual Pg.6 © 2019 Kevin O’Connor, London Power

WIRING CONVENTIONS (cont’d)
Impedance-matched: Balanced connections do not require balanced signals to function; rather, the more
important parameter is to maintain balanced impedances of the two lines. This is easily attained and is less
costly with respect to circuitry. The connector and cable types are the same as for the D.I. connections
above.
Ground-compensated: Ground-compensated (GC) connections allow unbalanced signals to be passed
between equipment without ground level difference impairment. The sending end requires a 3-wire male
connector, either 1/4"-TRS or XLR. The receiving equipment can have an unbalanced 2-wire connector,
such as female 1/4"-TS or female RCA phono input. The GC connection can be up to 15dB quieter than an
electronically balanced one.
For the ground compensation to be effective a 3-wire cable must be used. At the sending end, the cable is
wired the same as for the XLR or 1/4"-TRS above. At the receiving end, the “hot” goes to the tip (T) of the
1/4"-TS or of the RCA phono plug, while “cold” and the shield tie to the sleeve (S) of the connector.
GC outputs can be connected through a full 3-wire cable/connectors into a balanced XLR or 1/4"-TRS input
and provide an impedance-matched source signal.
Unbalanced: Unbalanced connections are also called “single-ended” or “2-wire”. Generally, one wire is
signal and the other is ground, as for the speaker connections above. Note that some speaker connections
might be floating, as when bridge-driven. The unbalanced output is either a female 1/4"-TS jack or female
RCA phono. The receiving end is identical. Guitar cables are typically 2-wire with just a single inner
conductor and a shield with male 1/4"-TS plugs for both ends. Hifi connections have historically been
similar cable but with male RCA phono plugs for both ends. Phono plugs and mini-plugs (1/8"-TS and 1/8"-
TRS) are common in semi-pro and home studios.
SIGNAL LEVELS: Note that the connector type used for any given input or output DOES NOT denote
the nominal signal level, despite common usage of certain connector types for certain nominal signal levels.
Neither does the application absolutely define the signal levels.
Instrument: -20dB = 77.5mVrms = 100mVpk
Semi-pro: -10dB = 210mVrms = 300mVpk
Line: 0dB = 775mVrms = 1V pk
“1-volt” Line: +4dB = 1.1Vrms = 1.6Vpk
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ICON Operating Manual Pg.7 © 2019 Kevin O’Connor, London Power

Section-3: RACK MOUNTING
This equipment may be rack mounted or used as a table-top device. Rubber feet are provided which bolt
onto the bottom cover for table-top or shelf use. Note that the washer under the bolt-head has its round-side
towards the rubber. Tighten the bolt just to the point where the rubber foot does not turn freely. DO NOT
over-tighten.
For rack mounting, some units have a storage area on the rear panel for the rubber feet. If the unit does not
have a storage position, such as on the 1U devices, place the rubber feet and their hardware in a ziplock bag
and store in a safe place.
The rack-mount brackets bolt to the sides of the unit and are interchangeable from left to right. Start all four
bolts before tightening any of them. The bolts should screw in freely without binding. Use appropriate bolts
and washers to secure the unit to the rack rails.
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ICON Operating Manual Pg.8 © 2019 Kevin O’Connor, London Power

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

Section-5: CONNECTIONS
All connections are made via rear-panel jacks. In a studio environment, it is common to use a patch bay for
access to equipment inputs and outputs, as the jacks in the patch bay are designed for repeated insert-extract
cycles. For a clean rack appearance it is preferred to have the wiring between the equipment and the patch
bay at the rear, allowing clear access to all of the front-panel controls.
Mains: AC Mains is connected via the female IEC connector at the left-hand end of the rear panel looking
from the rear. Use only an approved and intact IEC power cable with the appropriate wall-plug end for your
locale. Assure that the RANGE switch is set to the local mains voltage and that the front-panel Mains
switch is ‘off’ (out) prior to connection of the power cable. Use only a properly grounded AC source.
120-240: This is the AC RANGE switch which matches the power transformer in ICON to the nominal
local mains voltage. Move the slider to the correct position for the local mains voltage prior to connecting
the power cable to the amplifier or to the wall socket. Note that the range switch itself may be marked as
“115V” and “230V”, or have no markings.
120 - North America and parts of Japan rated at 100V
240 - Everywhere else and parts of Japan rated at 200V or higher
Input (1-6): This is the instrument signal input for the specified channel number. Use a standard guitar
cable or similar fitted with 1/4"-TS male ends. Input impedance to each channel is high enough to
accommodate a raw piezo pickup and have full tone capture.
Out (1-6): This is the output of the specified channel. Use a standard guitar cable or similar fitted with
1/4"-TS male ends. Output impedance is variable and should feed a nominally high-impedance
input.
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ICON Operating Manual Pg.10 © 2019 Kevin O’Connor, London Power

Section-6: PREAMP CHANNELS
All of the user controls are on the front panel. All of the input and output jacks are on the rear panel, as are
the tubes.
Channel-1: Fender Style
This is the classic Fender preamp architecture and values used in their amplifiers between the late 1950s to
present. We’ve added an output level control to provide extra versatility in the use of this channel. This
channel can be used as a boost into other channels or for external amplifiers, or as a power amplifier
“simulator” at the output of other channels. Channel-1 is also very pedal friendly.
Tube position V-1 on the rear panel is dedicated to Channel-1. Use 12AX7 or equivalent for the traditional
gain and tone. Use 12AT7 for reduced gain and a slightly rounder tone. Use 12AY7 for further reduced gain
and mellower tone, particularly for harmonica. 12AU7 provides the lowest gain and smoothest tone, similar
to a 50s-vintage octal preamp sound.
Drive: This control alters the signal level passed from the input stage to the second stage. High Drive
settings will create a warm clean sound to mild over-drive depending on the tube fitted, and how hot
an input is present.
Low: This control adjusts the amplitude of bass frequencies. Turn clockwise to increase and counter-
clockwise to reduce bass emphasis.
Mid: This control adjusts the level of mid-range frequencies. Turn clockwise to increase and counter-
clockwise to decrease emphasis.
High: This control adjusts the amplitude of treble frequencies. Turn clockwise to increase and counter-
clockwise to reduce treble emphasis.
Level: This control sets the output level for this channel, via OUT-1 on the rear panel.
To achieve a complete match to the iconic clean Fender sound, patch ICON Channel-1 through a tube power
amp fitted with 6L6s driving a relatively clean guitar speaker - specifically NOT a Celestion; rather, a
traditional Jensen, Electro Voice, JBL, Altec, “generic” Eminence driver or similar.
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ICON Operating Manual Pg.11 © 2019 Kevin O’Connor, London Power

PREAMP CHANNELS (cont’d)
Channel-2: Vox Top Boost Style
This is the classic Vox Top Boost preamp architecture and values used in their AC30 amplifiers between the
late 1960s to present. We’ve added an output level control to provide extra versatility in the use of this
channel. This channel can be used as a boost into other channels or for external amplifiers. Channel-1 is also
very pedal friendly.
Note that the “top boost” is not so much of a treble boost as it is a bass cut. The cathode-biased EL-84
output stages used in Vox amps tend to become more muddy sounding the harder they are driven. To
counter this, the preamp has to drive it then with much-reduced bass content to produce a net sound that is
balanced. With the popularity today of “18W” amps based on cathode-biased EL-84s, the top-boost preamp
is highly relevant.
Tube position V-2 on the rear panel is dedicated to Channel-2. Use 12AX7 or equivalent for the traditional
gain and tone. Use 12AT7 for reduced gain and a slightly rounder tone. Use 12AY7 for further reduced gain
and mellower tone, particularly for harmonica. 12AU7 provides the lowest gain and smoothest tone, similar
to a 50s-vintage octal preamp sound.
Drive: This control alters the signal level passed from the input stage to the second stage. High Drive
settings will create a warm clean sound to mild over-drive depending on the tube fitted, and how hot
an input is present.
Low: This control adjusts the amplitude of bass frequencies. Turn clockwise to increase and counter-
clockwise to reduce bass emphasis.
Mid: This control adjusts the level of mid-range frequencies. Turn clockwise to increase and counter-
clockwise to decrease emphasis.
High: This control adjusts the amplitude of treble frequencies. Turn clockwise to increase and counter-
clockwise to reduce treble emphasis.
Level: This control sets the output level for this channel, via OUT-2 on the rear panel.
To achieve a complete match to the iconic Vox Top Boost sound, patch ICON Channel-2 through a cathode-
biased tube power amp fitted with EL-84s driving a Celestion driver or similar.
Combine Channel-2 with a KT-77 power amp driving a Fane speaker for a Hiwatt clean tone.
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ICON Operating Manual Pg.12 © 2019 Kevin O’Connor, London Power

PREAMP CHANNELS (cont’d)
Channel-3: Marshall 800 Master Volume Style
This is the classic Marshall master volume preamp architecture used in their 2203 and 2204 amplifiers
between the early 1970s to present. This was an attempt to mimic the sound of an over-driven “plexi” amp
but with control over loudness, and is the basis for most high-gain preamps that followed. This channel can
be used as a boost into other channels or for external amplifiers. Gain is low enough that Channel-3 is still
pedal friendly.
The original architecture inverts the signal between the input and output of the preamp, so London Power
has corrected this to be non-inverting while retaining the same tone and gain. We’ve also fixed the problem
of tone controls that do very little, and ICON provides the best “Marshall” tone available.
Tube positions V-3 and V-4 on the rear panel are dedicated to Channel-3. Use 12AX7 or equivalent for the
traditional gain and tone. Use one or more 12AT7 for reduced gain and a slightly rounder tone. Use 12AY7
for further reduced gain and mellower tone. 12AU7 provides the lowest gain and smoothest tone, similar to a
50s-vintage octal preamp sound but here with a more modern voicing.
Drive: This control alters the signal level passed from the input stage to the second stage. High Drive
settings will create more saturated distortion tones.
Low: This control adjusts the amplitude of bass frequencies. Turn clockwise to increase and counter-
clockwise to reduce bass emphasis.
Mid: This control adjusts the level of mid-range frequencies. Turn clockwise to increase and counter-
clockwise to decrease emphasis.
High: This control adjusts the amplitude of treble frequencies. Turn clockwise to increase and counter-
clockwise to reduce treble emphasis.
Level: This control sets the output level for this channel, via OUT-3 on the rear panel.
To achieve a complete match to the iconic Marshall master volume sound, patch ICON Channel-3 through a
tube power amp fitted with true (skinny) EL-34s driving a Celestion driver or similar. Change to KT-66s for
a “vintage style” British tone that did not exist until the 2000s. Change to 6L6s to match the Peavey Butcher
tone, their copy of the 800.
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ICON Operating Manual Pg.13 © 2019 Kevin O’Connor, London Power

PREAMP CHANNELS (cont’d)
Channel-4: London Power Hot-rod Lead Style
This is the classic high-gain channel of the London Power Standard Preamp from the 1980s to present. This
channel represents many hot-rodded preamps of the 1980s and -90s and can be used on its own or with
external amplifiers. Despite its gain Channel-4 is still pedal friendly.
Tube positions V-5 and V-6 on the rear panel are dedicated to Channel-4. Use 12AX7 or equivalent for the
traditional gain and tone. Use one or more 12AT7 for reduced gain and a slightly rounder tone. Use 12AY7
for further reduced gain and mellower tone. 12AU7 provides the lowest gain and smoothest tone, similar to a
50s-vintage octal preamp sound but here with a more modern voicing.
Drive: This control alters the signal level passed from the input stage to the second stage. High Drive
settings will create more saturated distortion tones.
Low: This control adjusts the amplitude of bass frequencies. Turn clockwise to increase and counter-
clockwise to reduce bass emphasis.
Mid: This control adjusts the level of mid-range frequencies. Turn clockwise to increase and counter-
clockwise to decrease emphasis.
High: This control adjusts the amplitude of treble frequencies. Turn clockwise to increase and counter-
clockwise to reduce treble emphasis.
Level: This control sets the output level for this channel, via OUT-4 on the rear panel.
To achieve a complete match to the iconic London Power high-gain sound, patch ICON Channel-4 through
a tube power amp fitted with 6L6s driving a relatively clean guitar speaker - specifically NOT a Celestion;
rather, a traditional Jensen, ElectroVoice, JBL, Altec, “generic” Eminence driver or similar. Because of the
wide use of this preamp architecture, manufacturers matched the preamp through various power tubes and
speakers, meaning that many players did use the London Power preamp with Celestions for quite an edgy
tone that became iconic in its own right.
Combining Channel-4 with a KT-77 power amp and Fane loudspeakers produces the Hiwatt distortion
sound.
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ICON Operating Manual Pg.14 © 2019 Kevin O’Connor, London Power

PREAMP CHANNELS (cont’d)
Channel-5: Dumble Style
This is the classic over-drive channel of the Dumble amps from the 1970s to present and can be used on its
own or with external amplifiers. Despite its gain Channel-5 is still pedal friendly.
The original goal of the topology was to mimic the sound of an over-driven Fender amplifier but with
controllable loudness. This means that the EQ is early in the signal path and precedes distortion generation,
opposite to how most high-gain amplifiers are configured. Some voicing within the latter part of the circuit
smooths what could be a harsh tone. The EQ is configured in the “jazz” mode.
Tube positions V-7 and V-8 on the rear panel are dedicated to Channel-4. Use 12AX7 or equivalent for the
traditional gain and tone. Use one or more 12AT7 for reduced gain and a slightly rounder tone. Use 12AY7
for further reduced gain and mellower tone. 12AU7 provides the lowest gain and smoothest tone, similar to a
50s-vintage octal preamp sound but here with a more modern voicing.
Drive: This control alters the signal level passed from the input stage to the second stage. High Drive
settings will create more saturated distortion tones.
Low: This control adjusts the amplitude of bass frequencies. Turn clockwise to increase and counter-
clockwise to reduce bass emphasis.
Mid: This control adjusts the level of mid-range frequencies. Turn clockwise to increase and counter-
clockwise to decrease emphasis.
High: This control adjusts the amplitude of treble frequencies. Turn clockwise to increase and counter-
clockwise to reduce treble emphasis.
Trim: This control alters the signal level passed into the over-drive section proper and determines the
saturation of the distorted sound, depending on how Drive and Fat are set.
Fat: This control is an intermediate signal attenuator within the over-drive section and effects the
saturation level of the distorted sound depending on how Drive and Trim are set.
Level: This control sets the output level for this channel, via OUT-5 on the rear panel.
To achieve a complete match to the iconic Dumble jazz over-drive sound, patch ICON Channel-5 through a
tube power amp fitted with 6L6s driving a relatively clean guitar speaker - specifically NOT a Celestion;
rather, a traditional Jensen, Electro Voice, JBL, Altec, “generic” Eminence driver or similar. Some players
did use EL-34 amps and Celestions for a more edgy tone.
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ICON Operating Manual Pg.15 © 2019 Kevin O’Connor, London Power

PREAMP CHANNELS (cont’d)
Channel-6: Soldano Style
This is the classic high-gain channel of the Soldano SLO from the 1980s to present. This channel represents
many hot-rodded preamps of the 1980s to present and can be used on its own or with external amplifiers.
Almost any high-gain amplifier with a “mid-sucking” tone is a copy of the SLO.
Tube positions V-9 and V-10 on the rear panel are dedicated to Channel-4. Use 12AT7 or 5751* or
equivalent for the traditional SLO gain and tone. Use 12AX7 for harsher gain and tone as exhibited by the
Mesa Rectifier amps, Marshall SLX, Peavey and Fender 5150 variants, and countless other clones. Use
12AY7 for further reduced gain and mellower tone. 12AU7 provides the lowest gain and smoothest tone,
similar to a 50s-vintage octal preamp sound but here with a more modern voicing.
*5751 is listed as a “special 12AX7", however its mu is 70 as for 12AT7 rather than 100 as for 12AX7, In
this regard, the 12AT7 makes a better substitute for the 5751s Soldano originally used.
Drive: This control alters the signal level passed from the input stage to the second stage. High Drive
settings will create more saturated distortion tones.
Low: This control adjusts the amplitude of bass frequencies. Turn clockwise to increase and counter-
clockwise to reduce bass emphasis.
Mid: This control adjusts the level of mid-range frequencies. Turn clockwise to increase and counter-
clockwise to decrease emphasis.
High: This control adjusts the amplitude of treble frequencies. Turn clockwise to increase and counter-
clockwise to reduce treble emphasis.
Level: This control sets the output level for this channel, via OUT-6 on the rear panel.
To achieve a complete match to the iconic Soldano distortion sound, patch ICON Channel-6 through a tube
power amp fitted with 6L6s driving a relatively clean guitar speaker - specifically NOT a Celestion; rather,
a traditional Jensen, ElectroVoice, JBL, Altec, “generic” Eminence driver or similar. Many of the clones of
this circuit were matched up with EL-34 power amps and Celestion speakers for an edgier sound.
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ICON Operating Manual Pg.16 © 2019 Kevin O’Connor, London Power

FRONT PANEL REMAINDER
Mains: This is a push-on/off switch to connect the AC mains to the power transformer. Power is ‘on’ when
Mains is ‘in’. Mains ‘out’ is power-off. The LED will illuminate when power is ‘on’.
ICON uses zero power when Mains is ‘off’.
All of the controls and switches can be set in any combination that sounds good.
Section-7: SYSTEM CONFIGURATIONS
ICON can be the basis for very simple or elaborate tone generation systems for musicians or studio
personnel.
NOTE !!! Turn off phantom power to any mixer channel that does not require it !!!
In any of the configurations below, any output may be connected to a mixing console while other outputs are
used for local monitoring, or not used at all. The presence of +48Vdc phantom voltage on the mixer input
can damage most preamplifier outputs, active guitar preamps and passive guitar pickups. It is good practice
to default to PHANTOM=OFF unless a specific microphone requires it.
USE A PATCH BAY
It is strongly recommended that ICON’s inputs and outputs be connected to an external patch bay,
especially in the studio environment or wherever frequent plugging-in and unplugging is expected. Patch
bays have much more durable jacks than do most amplifiers or preamplifiers, as patch bays are specifically
designed for high cycle rates.
Preamp-Only
The simplest configuration is to use the preamp alone to generate the complete sound, with one of the
channel Outs fed to a stereo, mixer or other type of monitoring system incorporating full-range
loudspeakers. In such a system, it is likely that a low-pass filter would be employed to give a sound similar
to using a guitar speaker. Such a system used live is referred to as an “ampless stage setup” as the usual
back line of amplifiers and speaker cabinets for the individual instruments is not used; rather, the musicians
rely on stage monitors or in-ear monitors to hear their own instrument and the rest of the band.
Because ICON has six independent channels, up to six players can use it simultaneously provided they do
not mind the distinct tones of each channel. The original guitar amplifiers were designed to be used this way,
and often had inputs labelled for guitar, bass, accordion, microphone, and even record players. If one wanted
to make some of the channel tones and gains more similar, particularly for the higher-gain channels, one
only has to change the tubes of one or more channels to low-mu types.
For a live-use system or for recording, ICON can be connected to a power amplifier driving guitar speakers,
in which case no additional EQing is required.
How the extra EQing is achieved depends on which channels of ICON are used.
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SYSTEM CONFIGURATIONS (cont’d)
For example, Channel-1 provides a traditional Fender clean sound and when used this way may require no
further EQing. On the other hand, in a combo amp, which is how most players are used to experiencing this
preamp, the speaker rolls off a lot of treble, so we might want simply to adjust Channel-1's High control
lower than usual. This may suffice or not. If not, we can add an external equaliser unit between Out-1 and
the monitoring system, or connect Out-1 into one of the other channels of ICON.
Channel-2 provides a very bright sound that may be too thin on its own, especially through a full-range
system, consider cascading it with Channel-1 for some fattening and balancing.
You may also use either Channel-1 or channel-2 as a boost into the other channels for heavier distortions
than they would otherwise produce on their own. This will have a diminished effect for Channel-6 as the
second in the chain, especially if Channel-6 is fitted with 12AX7s or equivalent. Low-mu tubes in Channel-6
will allow the player to better hear the difference that adding Channel-1 has made.
You may reverse the cascaded connections above so that the high-gain channel drives Channel-1 instead.
This gives an opportunity to use Channel-1 like a power amplifier simulator, where Channel-1 smooths the
edgy output of the high-gain sound, just as the power amp does in the iconic integrated amplifier.
It is an irony that the high-gain channels were designed to mimic the sound of an over-driven amplifier but
with control over the resulting loudness, and played through a power amplifier running clean. That power
amp added its own veil of character and smoothing to the preamp sound, and this aspect of the iconic tone
may be missing from the respective preamp-only tone. We are not cascading the high-gain preamp into
Channel-1 say, for more gain, but rather to smooth the edges of the sound. Because Channel-1 has its own
Drive and Level controls, we can overdrive it, as many players over-drove their amps on stage.
However the player chooses to use the channels is up to his or her need at the time.
For recording personnel, ICON provides a very easy way to have tube-based tones of a wide variety without
having to change control settings between sounds. ICON can also be used to warm up digital recordings or
previously captured digital sounds.
Many players like to use different amplifiers for different kinds of sounds, such as a Fender-style amp for
clean and a master-volume amp for distortion, through separate speakers. ICON has these different style
preamps, so all the player has to do is add separate power amplifiers and speakers to suit his needs.
An example system might have Channel-1 through a 6L6-fitted power amp for a clean path, Channel-2
through an “18W” EL-84 amp for a dirty rhythm sound, and any of Channels 3,4 or 6 through a third power
amp for a lead sound.
The preamp alone can be used for recording at home or in the studio and lends itself well to the “silent”
recording method of monitoring through headphones. Note that it is never quite good enough to rely on
headphones alone when recording; rather, use near-field monitors or full loudspeakers for part of the mixing
process to get things right. Pure headphone mixes never sound correct through real speakers.
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ICON Operating Manual Pg.18 © 2019 Kevin O’Connor, London Power

SYSTEM CONFIGURATIONS (cont’d)
Adding Effects
In any of the scenarios above, one can add effects ahead of or after the preamp and have all of the benefits
of the system described. The effect’s audibility will depend on the gain of the channel.
For example, Channels 1&2 both have low gain, and effects will come through very nicely. Channels 3,4&5
have more gain but front-loaded effects will still be compelling. Channel-6 will accommodate delay pedals in
front, but tonal effects such as phasers, flangers, boosts and compressors may not be quite as noticeable.
Traditionally, guitar players use front-loaded effects - and still do for the most part. The “studio method”
splits up effects by placing tonal modifiers in front of the preamp and time-based effects after. The preamp
is nominally where the bulk of the guitar’s tone is created, whether as a clean sound or a distorted one, so
the preamp is often referred to as the “tone generator”.
Switching Between Channels
ICON has no internal switching; rather, it is simply six building blocks that can be used however the player
or recording engineer wishes.
The simplest switching form is to plug into whichever of ICON’s channels one wishes to use at the moment,
then unplug and replug into another channel as required. However, this will wear out the input jacks very
quickly!
A preferred method is to use an external switching system, of which many are available these days, and/or to
use signal splitters and mixers at the input end and output end, respectively. In one possibility, a signal
splitter can feed the instrument signal into as many of ICON’s channels as will be used, while a mixer
selects the desired output using its built-in muting switches and/or volume sliders. A refinement of the above
is to replace the mixer with a selector that feeds the selected channel output to a monitor amplifier and
speaker. The latter method is more favourable for live use. In any of these configurations, effects may be
cascaded in front of ICON’s channels and/or after ICON, being selected automatically with the channel.
Similarly, in a multi-amp system, an input splitter/selector/director may be the switching system, with each
subsequent path comprised of effects, a channel of ICON, possibly more effects, and an amplifier and
speaker dedicated to each sound. In some cases, the player may combine a clean sound from one amp with a
distorted sound from another, where the two sounds mix acoustically in the air and there is a sense of
“stereo” depending where the player or other band mates are located.
Note that where players find such a system easy to understand and satisfying to assemble and use, sound
men tend to dislike having to provide more than one microphone per instrument as it is then impossible to
change that player’s level in the mix using a single slider. More elaborate mixing boards have sub mixers
and even fully independent mixers within, which readily accommodate this situation.
Note also that even though every modern mixing console has stereo outputs and many stereo inputs in
addition to pannable mono inputs, stereo sound in a live situation does not translate well to the front-of-
house sound or to the audience.
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ICON Operating Manual Pg.19 © 2019 Kevin O’Connor, London Power