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If you have tried everything and the meter light is
working one or both of the internal fuses may have
blown. They are located inside the amplifier and
should be replaced by a competent engineer.
Replacements free on request from Icon Audio.
Distorted sound.
Try another source; if sound improves then it’s probably
something wrong with the first source. If no improvement
try different speakers, if no improvement could be an
amplifier problem.
Hum Problems
If you experience hum, try disconnecting all inputs, if
hum persists this is probably an amplifier fault.
If not, identify which input is causing hum. Connect one
input at a time. A common cause is a ‘hum loop’ caused
by having too many earths, and may be identified by
unplugging each input source from the mains. One
remedy for this is to use an interconnect which only has
the screen connected at one end. Other causes of low-
level hum can be from adjacent equipment, so
experiment with moving equipment around to see if this
makes the hum better or worse.
Interference Problems
The amplifier design incorporates features and devices
which make it resistant to mains-born interference. But
some heater boilers/fridges/cookers etc can generate RF
(radio frequency) interference which travels through the
air (and walls). Although rare this can be very irritating.
In this case a simple capacitor is often all that is needed
to effect a permanent cure (contact us).
One channel missing.
Usually ‘bad’ connection on either the input or the
speakers. Try swapping the connection over to establish
if the cause is:
(a) Input to the amp.
Sound will move to the other
channel.
(b) Amplifier or speakers.
Sound will not move.
(c) If none of these, check internal fuse for that channel
(see section 5.2).
Strange noises coming from speakers:
Turn volume to minimum on unused input, if problem
corrected either fault with source unit or with connection.
If noise persists, problem with amplifier.
If a whole output valve glows red (other than the heater),
often accompanied by a hum through the speakers,
switch off immediately, and refer to Icon Audio or a
service engineer, as this could be valve failure.
A valve that is lit up is not a guarantee that it is working
properly; conversely a valve that is not lit up will not be
working (usually cold to the touch).
Valve Replacement
(see also section 7)
Valve life will depend upon such things as hours of use
and number of on/off cycles, Do not switch on and off
unnecessarily (see
Standby).
Also it is not good practice
to remove the valves unnecessarily as this can strain the
pins and cause tiny air leaks.
Service:
Should you suspect a problem, you could
return the unit to Icon Audio for a periodic service or
return the valves for testing free of charge. You should
carefully remove the valves (the KT88s should be held
by the base when removing, to prevent damage)
numbering them with a marker from left to right as you
do so in order that that may be replaced in the same
position. They should be well packed in cardboard &
foam or similar, and returned to Icon Audio for
testing. (Valves are very rugged if packed properly).
Mains Supply
This amplifier is configured to work on 230/240v ac,
(or 117v USA, Canada) this may be changed over.
Contact us for more information.
6. Bias Checking & Adjustment
If you are unsure about any aspect of bias
contact your retailer, Icon Audio or a competent
service engineer.
The Stereo 40 MK IV
uses the ‘Fixed bias’ method
of valve operation. This has the advantage of
higher power, lower feedback and cooler running.
However you should regularly check the bias
reading using the built in meter to ensure best
performance from the amplifier.
This is very easy.
1,
Tools you will need:
A small flat blade screwdriver ( normally supplied).
2,
How to read the meter.
If possible warm up the amplifier for 10 minutes.
Standby “off”, in Ultralinear mode, volume at “zero”.
Rotate the bias knob through V1-V4. This
corresponds with the rear output valves left to right
(viewed from the front). Each valve should have the
black pointer in or near the black section. (50-75).
About 10% percent difference ON EACH PAIR (1,2
and 3,4) will make little difference in performance.
Greater than this requires adjustment, especially if
the reading is 80 or more it should be reduced as this
valve is drawing too much current. Lower than 50 will
cause no harm but the performance will be reduced.
NOTE
3. The readings are affected by your local mains
voltage. So if they are all slightly high or low this is
probably OK, and check again later. If one valve is
giving a high or low reading it is easier to adjust that
one valve in line with the others.
4.
How to adjust the bias:
Make sure you are reading the valve to adjust, e.g.
read V1 to adjust V1 screw. If the reading is
incorrect, set this by using the screw very slowly up
or down until the correct reading is obtained. They
are very sensitive so adjust very carefully. If the
reading appears a little unstable this is normally due
to mains fluctuations.
You may need to repeat this a couple of times as the
adjustment of one valve may affect the other
readings slightly.
5, If one or more valves are showing erratic readings
or you cannot set the correct voltage, then that valve
is probably faulty or out of specification. If you are
unable to set the reading high enough this means the
emission of the valve is too low. Normally adjustment
intervals are 2-3 times a year or if you suspect a
problem.
6.
Possible problems:
If the reading is unstable,
100%, or “zero %” this is probably a valve failure, in
which case refer to your dealer or Icon Audio. Also
the internal HT fuse may have blown (spares inside).
When not reading bias, the meter on the front panel
gives an approximate power indication. (Full power
both channels in mono = 100%).
