*See engineers notes at rear
Page
5
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
MB30m power amplifiers require some kind of pre
amplifier to accomplish volume control and
switching of source. This can 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. Any of our highly rated
PS1 MM/MC, PS2 MM or PS3 MM/MC all valve
phono stages would be an ideal partner.
Note:
If you are only using one source that has a
volume control fitted, e.g. our PS1 or PS3 phono
stage, or a CD player with volume control then no
preamplifier is necessary.
Connecting loudspeakers
It is important to use good quality loudspeaker
cable. This should be relatively thick and multi-
stranded. i.e. QED 79 “stand” or better. Take care
to connect the correct polarity.
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.
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.
Speaker polarity.
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), a test disc will be helpful. If
you are
‘bi-wiring’
you can independently use
either 4 or 8 ohms for the bass and treble. Many
modern smaller speakers use a 4 ohm unit. If in
doubt the “heaviest” base is the best match
(depending upon preference). and again 4 or 8
ohms for treble, 8 ohms will give a “brighter”
balance. There is no right or wrong so choose the
sound balance that suits you best.
The MB30m 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 85db 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 regularly or if you have cause to suspect a problem
Do Make sure the speakers are in phase
What is safe maximum power?
The MB30m will run happily all day long at any
undistorted 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
Do not leave the amplifier on 24/7. There is no
benefit, it is wasting electricity and valve life. The
MB30 only needs one minute to warm up and 15
minutes to sound at its best. Valve life is approx
5000 hours, that is approx 7 months continuous
use or 5 years at 20 hours a week.
