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3 Connecting inputs & outputs
Many problems associated with electronic equipment
involves connecting leads, which are usually either
‘BAD CONNECTION’ or ‘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 passive and
active 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. Our PS1.2 MM/MC or PS3 MM/MC
all valve phono stages are 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.
As all cables have losses, keeping the speaker
cables short is best. It may be better and be cheaper
to re-arrange your room and use shorter cables than
to spend a fortune on longer cables!
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).
WARNING 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 MB90s 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 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
Ωohms. The best power
match is (1) the loudest, and (2) the most pleasing
tonal balance.
The MB 90 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.
4 Getting the best performance from your amplifier
•
Switch on your pre-
amp first. This will limit “switch on thump” in your speakers.
•
Use the “Standby” switch before switching power on, this will protect the output valves
•
Do not leave the amplifier switched on all the time. The valves wear out faster
•
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 switch from Ultralinear to Triode without first switching
to “Standby”
•
Do not operate the amplifier without loudspeakers connected
(unless temporarily at “0” volume)
•
Do not use valves other than listed as there could be danger of shock or damage
•
Do check the bias regularly (at least once a month) to be sure of optimum performance.
•
Make sure the speakers are in phase
(see speaker polarity above)
•
Use the best possible source material for setting up and testing your system
What is safe maximum volume?
The MB 90 will run happily all day long at a high
undistorted volume; 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.
Triode Switch.
This switch causes the KT150/120s
to operate as Triode valves.
As switching
“live”
could damage the output transformers. Switching
should only be done when the amplifier is in the
“standby” mode or switched off.
The volume will
remain virtually the same, but the maximum output is
reduced by approximately 50%. The characteristics
of a “Triode” amplifier are different from the