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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
The amplifier will work with any standard piece of
hi fi/audio e.g. CD, Phono pre-amp, Tuner, Tape
Deck, Mini Disc, TV, Video Recorder, DVD etc
having an output of 300mv or more.
All the inputs are technically the same.
If you wish to use a turntable you will need a
suitable phono pre-amp. Your dealer or Icon
Audio can advise you. Our new PS1 MM/MC all
valve phono stage is an ideal partner.
To use as a power amplifier.
As the ST25 is essentially a power amplifier with a
volume control, the volume control will be virtually
invisible to the pre-amplifier if turned to the full
clockwise position. If you have too much gain,
“back off” the volume no more than necessary. If
you still have too much gain Icon Audio can
modify the sensitivity to your specification. The
tape input will provide the most direct signal path.
Good quality leads should be used, making sure
that you have good connections at both ends.
If the amplifier is permanently required to work as
a power amplifier, we can modify to your
specification. This is then easily reversible.
Connecting a tape deck.
(Or CDRW/MP3 etc)
The STEREO 25 will work with any tape deck
having suitable output, it is not possible to record.
Connecting loudspeakers
It is important to use good quality loudspeaker
cable. This should be relatively thick and muti-
stranded. i.e. QED ‘Classic’ 79 strand or similar.
Take care to connect the polarity correctly. 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 very
tolerant of cables, therefore the benefits of some
very ‘exotic’ cables may be negligible 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).
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
damage
the
valves.
Alternatively use good quality ‘banana’ plugs or
spade connections, once fitted they are trouble
free.
Speaker polarity. It is essential that you
observe the polarity of the terminals; they
must be the same for the left/right connections
at the 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.
The STEREO 25 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.
Headphone Operation
The ST25 II incorporates a high quality
headphone circuit that uses dedicated low output
windings within the output transformers to give the
same pure valve sonic signature that we are
famous for. Matching will suit 16 to 300 ohm
headphones, but virtually any impedance may be
used. Better results will be obtained with low
efficiency types. Due to the compromises
necessary in “building in” a headphone circuit in a
high power valve amplifier, the noise floor will
always
be a little higher than a “stand alone”
headphone
amplifier,
but
under
normal
circumstances this will be negligible.
“iPod” type earphones will work OK although you
may need a 3.5mm
– ¼” stereo jack adaptor to fit
the ¼” socket. For best results use 60 Ohms or
more.
Don’t forget to switch off the speakers!
