icon Audio LA 4 MK II User manual

Page 1
icon Audio
LA 4 MK II
Pure Valve Line Preamplifier Instructions
About the LA 4 MK II
Thank you for purchasing one of our amplifiers, a lot
of care has gone into the design, selection of
components and production of this amplifier. We are
sure that you will hear the difference.
To get the best out of the LA4 MK II. Please read the
enclosed notes. We have tried to give you all the
information you need. We would recommend that
everyone follows the ‘quick set up guide’. Should
you be uncertain about anything to do with your LA4
MK II please contact your dealer.
The LA4 MK II is a line amplifier designed to
complement high quality valve or transistor power
amplifiers requiring an input voltage of 1volt or
greater. A high and low gain switch excellent
matching to low and high sensitivity power amplifiers.
Also an attenuated lower level output is also provided
for more sensitive amplifiers like Leak, or integrated
amplifiers.
Our philosophy is to use traditional valve minimalist,
circuitry. The beauty of valve amplifiers is that they
are usually very simple; therefore with the use of
traditional point-to point construction, modern high
performance low tolerance components, it is possible
to achieve very high sonic performance. This
simplicity enables us to avoid the use of printed
circuit boards, which are not ideal for valve amplifiers
despite their common use.
Although technical performance is important, we
never forget that sound quality takes overriding
priority in our design and production. The LA4 MK II
has a massive overload capability and even then
would go into ‘soft clipping’, which is much more
benign and easier on the ear than overloaded
transistors.
The simplicity of the circuit means that there are
much fewer components for the signal to pass
through, fewer connections and switches, again
adding to the purity of sound. This simplicity also
means that we can use higher quality oversized
components, such as 2w resistors.
The use of popular valves, which are still in
production, means that obtaining replacements is
easy and inexpensive when necessary.
In the process of building the LA4 MK II to its high
standard no corners have been cut and we have also
paid close attention to the appearance.
The remote control has its own separate power
supply so the operation will not influence sonic
qualities.
The final result is an amplifier with excellent
characteristics, with an accurate yet smooth and
transparent quality.
The circuit is almost identical to the LA4 MK1, the
changes being variable gain and the excellent 274B
rectifier.
Various upgrades are available at the time of
ordering or may be retro fitted. These include
“Jensen” capacitors and various valves including
“Full Music” which will enhance the performance of
the LA4 MK II.

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Final Inspection
This amplifier has been carefully checked, tested and final adjustments made by Icon Audio in
Leicester.
It has passed our rigorous listening test and final inspection to assure you of optimum
performance and reliability.
Date …./…./….
Model ……….
Amp Serial Number ……….
Customer ……………………………
Check amplifier finish ……….
Run 6 hour test ……….
Check all inputs & tape monitor ……….
Sound Quality ……….
Channel Balance ……….
Valve Microphony ……….
Valve Seating ……….
Hum & noise level ……….
RF Test ……….
Remote Control Function ……….
Remote control in box ……….
Serial No sticker and recorded ……….
Mains voltage 110 / 230-240V
IEC socket Fuse ………A
Sales invoice ……….
Credit card receipt .………
Bias meter N/A
Transformer Protection N/A
Upgrades:
Input valves ……….
Output valve ……….
Rectifier valve ……….
Capacitors ……….
Interconnects ……….
Signed off by ……………………….
Notes:

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QUICK SET UP GUIDE
1 Unpack unit carefully. Make sure that it is in good
condition. It is important that you keep packaging for
warranty/service return.
2 Fit the rectifier valve 274B.
BEWARE ONLY FIT IN REAR CENTRE (see pic P1)
Otherwise the unit will not function, and damage to
both valves and unit will result. The valves are
normally numbered in order that they will be in the
same position when tested and aged. The 6SN7s are
normally left fitted. If there is no special order. Do not
pull the 6SN7s by the glass envelope! This could
cause the glass envelope to become detached from
the base causing irreparable damage. Be careful to
align to “spigot” of the valve with the socket before
pushing in to place.
3 Connect to source & Output units, e.g. CD,
Tuner, Tape, Phono pre amp (if used) and power amp
etc via appropriate phono sockets and leads. OUT 1
is the high level output for ICON MB25s etc. OUT 2 is
a lower level, if you are not sure choose the output
that gives best results.
4 Connect to mains supply using supplied IEC
mains lead to 240v supply. If for some reason the
welded plug must be removed, please remove
fuse and dispose of immediately. (As they can be a
danger to children if plugged in). The replacement
plug should be wired in the following way Brown to
Live terminal, Blue to Neutral terminal and
Green/Yellow to Earth terminal.
6 SWITCH ON! The blue mains indicator should light
up and unit will take approximately 40 seconds to
start working. All valves should have a visible orange
glow from the cathode heaters. With the volume
control set to minimum (fully anti-clockwise) there
should be no sound coming from the speakers except
a barely discernable gentle hum.
7 Your unit should now be functioning. If not check
wiring again and/Use selector/tape monitor/volume to
choose source program and suitable listening volume.
The best sound quality will be when the unit has
warmed up for at least 20 mins.
8 Health and Safety. The valves when operating
have high surface temperatures. Keep out of reach of
children and pets. The use of the optional guard is
recommend in these circumstances. Always unplug
when making adjustments. Like all amplifiers there
are potentially lethal high voltages inside (400v
DC), which when switched off can take up to 15
mins to discharge! Do not remove bottom panel
unless you are a competent engineer. There are no
user serviceable parts inside. Like other household
electrical appliances do not leave unattended
whilst switched on.
Connecting inputs & outputs
Many problems with hi fi equipment involve
connecting leads which are usually either ‘Bad, or
Wrong connection’. So it’s worth making sure that
you have good connections and that your leads are
the right way round.
Inputs
The amplifier will work with any standard piece of hi fi
e.g. CD, Tuner, Tape Deck, Mini Disc, TV, Video
Recorder, DVD etc having an output of 200mv or
more, to get full power. The position of the volume
control will vary with the input voltage of different
units, this has no effect upon performance.
If you wish to use a turntable you will need a suitable
phono pre-amp. Your dealer or Icon can assist you.
Connecting a tape deck
The LA4 MK II will work with any tape deck having
suitable output, and it is possible to record from any
connected source using the terminals marked ‘Pre-
out’. The LA4 MK II has a ‘Tape Monitor’ facility,
which enables you to use a ‘three head deck’ or an
equalizer.
Some tape decks ‘Present a load’ to the amplifier
terminals, even when not in use, which can affect
sound quality. (You can do an audible check for this
by removing the input and listening for a change in
sound quality). If so remove when not required.
General points
 Switching the pre-amp on before the power amp
will reduce “switch on thump, of the speakers”
 Mobile phone ‘breakthrough’ is normal
 A switch-off ‘click’ through the speakers is
normal.
 Storage in damp conditions could damage
transformers.
Connecting Leads
Use good quality connecting leads, which are no
longer than they need to be.
Leaving the amp switched on
People sometimes ask if the amp should be left
running 24/7 without switching off. Whilst the amplifier
will sound at its best when it is properly warmed up,
there is no advantage leaving it switched on when it is
not in use. It is using electricity and valves have a
finite life. Conversely the valves and other
components are stressed more at switch on; therefore
do not switch on and off unnecessarily. Although the
amplifier should sound good within about 20
mins, like most hi fi units it can take up to an hour
to sound at its best and will take a couple of
months of regular use before it is ‘run in’.
Cabinet Care
To remove dust from the cabinet and valves we
suggest gentle brushing with a soft paintbrush and a
duster. Finger marks can usually be removed with a
damp cloth. The Perspex valve cover (if fitted) may
need a gentle wipe with soapy water and drying with
a duster. On no account use anything wet on the
amplifier, and always clean with the power
disconnected.
CAUTION – HEALTH & SAFETY!
When making any adjustments remember to
isolate from power supply, and remember that
high voltages can remain present inside for some
time after switch off.

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Trouble Shooting
Amplifier Dead
Check the 1amp mains fuse at the back of the
amplifier. To gain access, remove the mains lead.
The fuse is in a small plastic drawer, which forms part
of the socket assembly. To open insert a flat bade
screwdriver or similar and prise open. The fuse in
use is the innermost the outer is a spare. Should the
replacement fuse also blow there is a fault.
Replacements should be 1Amp ‘anti-surge’.
The fuse in the mains plug should be a 3 or 5 amp
fuse, although unlikely, this should be checked if the
amplifier fuse is OK.
No sound
Have you selected the right input? Are the
connections OK? Is everything switched on? Are the
speakers connected?
Distorted sound.
Try another source; if sound improves then it’s
probably something wrong with the first source. If no
improvement try different speakers, if no improvement
could be an amplifier problem.
Hum Problems
If you experience hum, try disconnecting all inputs, if
hum persists this is probably an amplifier fault.
If not, Identify which input is causing hum. Connect
one input at a time. A common cause is a ‘hum loop’
caused by having too many earths, and may be
identified by unplugging each input source from the
mains. One remedy for this is to use an interconnect
which only has the screen connected at one end.
Other causes of low-level hum can be from adjacent
equipment, so experiment with moving equipment
around to see if this makes the hum better or worse.
One channel missing.
Usually ‘bad’ connection on either the input or the
speakers. Try swapping the connection over to
establish if the cause is:
(a) Input to the amp. Sound will move to the other
channel.
(b) Amplifier or speakers. Sound will not move.
Strange noises coming from speakers
Turn volume to minimum on unused input, if problem
corrected either fault with source unit or with
connection. If noise persists, problem with amplifier.
A valve that is lit up is not a guarantee that it is
working properly; conversely a valve that is not lit up
will not be working.
Valve Replacement (see also section 2)
Valve life will depend upon such things as hours of
use and number of on/off cycles. As all the valves are
lightly loaded we would estimate life of approx 4 to 10
years. It is essential that only the correct valves
are used as some similar looking valves have a
different pin connection and insertion could result
in damage to the amplifier and risk of electric
shock. It is not good practice to remove the valves
unnecessarily as this can strain the pins and cause
tiny air leaks. Icon Audio are happy to replace valves
and check to performance of your amplifier, and
advise on the latest upgrades available.
Although the three original 6SN7 valves are normally
identical it is important that if they are removed, that
they are replaced in the same position. We normally
number them.
Service: Should you suspect a problem, you could
return the unit to your dealer or Icon Audio for a
periodic service or return the valves for testing free of
charge. You should carefully remove the valves, they
should be well packed in cardboard & foam or similar,
and returned to Icon Audio for testing. (Valves are
very rugged if packed properly).
Specification & Features
 No printed circuit board or tag board
 Japanese Blue ALPS volume pot.
 All Triode design
 Valve rectifier, 274B
 Twin choke power supply
 3x 6SN7 Double triode
 Signal to noise level -90db
 Infra red remote control, volume up/down, mute
 Freq response 10hz-30khz +0 - 0.1db
 THD 0.01%, @ 1khz, 2v rms
 Hand wired point to point components
 High quality 2w metal film resistors, for audio
 Blue LED mains indicator
 Audio grade Polypropylene audio capacitors
 Jensen Copper foil in paper (option)
 Wired with silver PTFE audiophile cable
 Rubicon/Nichichron power capacitors
 Inputs, CD, Tape, Tuner, Aux, Phono (line level)
 Ceramic valve holders for minimum leakage
 DC heater power supply for minimum noise.
 Gold plated Input & output terminals
 Tape monitor circuit
 Max Gain= 12db (4x Low), 18db (8x High)
 Output impedance 38 ohms
 Maximum output 30 volts (OUT1) 5v (OUT2)
 Optional safety guard
 Transformers & choke resin sealed to minimise
noise & hum.
 230/240volts, 35watts 1A anti-surge fuse
 IEC mains lead, (5amp fused)
 C E certified
 250W, 370D, 230H with 274B (or 175 with
GZ34) 12kg packed. Allow for rear connections &
ventilation)
(Specifications subject to change, errors & omissions excepted 25/04/17)
icon Audio (UK) Ltd
351 Aylestone Road Leicester LE2 8TA UK
www.iconaudio.com
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