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Many
problems
associated
equipment involves connecting leads, which are
usually
either
'BAD
'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 makes ideal
pre amps. 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 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
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 845 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
*See engineers notes at rear
3 Connecting inputs & outputs
with
electronic
CONNECTION'
or
touching could cause damage. Alternatively use
good quality 'banana' plugs or spade connections,
a
once fitted they are trouble free.
Speaker polarity. When using a pair of MB845s
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, 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 845 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 84db 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.
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
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