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3 Connecting inputs & outputs
Many problems associated with electronic
equipment involves connecting leads, which are
usually either
‘BAD CONNECTION’ or a
‘WRONG CONNECTION’
. So it’s worth making
sure that you have good connections and that
your leads are the right way round.
Inputs
These power amplifiers require some kind of pre
amplifier to accomplish switching and volume
control. This could either be achieved by either a
“passive” or powered unit. Icon Audio make ideal
pre amps (Icon Passive or LA4 MKII) . You may
wish to consult your dealer. If you wish to use a
turntable you will need a suitable phono pre-amp.
Your dealer or Icon Audio can advise you. Either
of our highly rated PS1 or PS3 MM/MC all valve
phono stages would be an ideal partner.
Connecting loudspeakers
It is important to use good quality loudspeaker
cable. This should be relatively thick and muti-
stranded. i.e. QED ‘Original’ or better. Take care
to connect the correct polarity. The use of
‘Banana plugs’ or ‘spade’ connections will ensure
a good connection whilst minimising the risk of
‘shorts’.
In our experience Icon valve amplifiers are more
tolerant of cables, therefore the benefits of some
very ‘exotic’ cables may be less apparent. But this
is also personal taste. The losses in speaker
cables is normally less than in interconnects.
You can either ‘hard wire’ your cable to the
amplifier by baring enough cable to fit in the
connector and twist together to avoid any spare
strands touching anywhere else (soldering the
stands together helps).
Be warned this amplifier
does not have an output protection device,
which would degrade the sound. So a
prolonged short due to strands of wire
touching could cause damage.
Alternatively use
good quality ‘banana’ plugs or spade connections,
once fitted they are trouble free.
Speaker polarity. When using a pair of
MB845is it is essential that you observe the
polarity of the terminals; they must be the
same for the left/right connections at each
amplifier end and at the loudspeaker end
.
Otherwise the sound will be ‘out of phase’ with the
sound stage ‘inside out’ with reduced bass.
If you
are unable to check this or confirm the polarity
(e.g. if you have ‘built in’ wiring), try the following;
Connect the system up and play some music with
plenty of bass (e.g. dance music), preferably in
mono (FM tuners are usually switchable to mono)
and stand the speakers close together. If correct
you should hear plenty of bass, if not
reverse the
terminals for one channel only, either at the
amp or speaker.
You will now hear more, or less
bass. The higher bass output is the correct setting
to use. Another alternative is to use a test disc. If
you are ‘bi-wiring’ your speakers use only two
terminals, you must use only 4 or 8 ohms (plus “0”
black terminal), not both, as this will not load the
amplifier properly.
4 or 8 Ohms?
Many modern loudspeakers have an impedance
which can vary from 2-16 ohms. The best power
match is (1) the loudest, and (2) the most pleasing
tonal balance.
The MB 845i is designed to work with full range,
low to medium efficiency speakers having
impedance between 4 ohms to 8 ohms. Speakers
having efficiency of lower than 86db will have
greater difficulty in providing a high sound level.
But this will also depend upon individual speakers,
room size, type of music and positioning etc.
4 Getting the best performance from your amplifier
UNDER NO CIRCUMSTANCES OPERATE WITHOUT VALVES FITTED!
NEVER REMOVE THE BOTTOM COVER
Switch on your pre-amp first. This will limit “switch on thump” in your speakers.
Do not leave the amplifier switched on all the time. This is not necessary
Do not switch off and on without a short rest of 60 seconds (to reset the ‘soft start’)
Do not adjust the output valve grid bias without reading the manual
Do not operate the amplifier without loudspeakers connected
Do not use valves other than listed as there could be danger of shock or damage
Do check the bias once or twice a year or if you have cause to suspect a problem
Make sure the speakers are in phase
What is safe maximum volume?
The MB 845i will run happily all day long at
maximum power; the valves hardly stressed any
more than at zero volume. Running into distortion
will however stress the whole amplifier. Generally
speaking if the sound is not distorted then the
amplifier is not stressed. But beware of heavy
musical transients at high volume which could
also damage your speakers and blow fuses.
Leaving the amp switched on
We are often asked if the amplifier 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
