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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 

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 
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  PS1/2/3  MM/MC  all 
valve phono stages are ideal partners. 

 

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). 

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.  

 

Speaker  polarity.  When  using  a  pair  of 
MB150Ss  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  2-16ohms.  The  best  power 
match is (1) the loudest, and (2) the most pleasing 
tonal balance. 
The  MB150  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. 

  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 switch from Ultralinear to Triode without first switching 

to “Standby” 

  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 

  Use the best possible source material 

 

What is safe maximum volume? 

The  MB150  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 

musical  transients  at  high  volume  which  could 
also damage your speakers and blow fuses. 

 

Triode Switch. 

This switch causes the KT120s to 

operate  as  Triode  valves. 

As  switching  can 

stress  the  output  transformers  switching 
should  only  be  done  when  the  amplifier  is  in 
the  “standby”  mode  or  switched  off.

  The 

Summary of Contents for MB 150

Page 1: ...ied to include everything that you need to know Please let us know if you find any errors or feel that we have missed anything out Hi fi reproduction is a long chain of events that includes the recording editing mixing etc before being transferred to a medium such as LP Digital etc before being played through your own source unit the amplifier and finally loudspeakers Your room acoustics will affe...

Page 2: ...un min 6 hour test Check input Output Valve Bias level v Sound Quality Channel Balance Valve Microphony Valve Seating Hum level mv RF Test LED brightness Serial No sticker and recorded Mains voltage 110 230 240V IEC Mains Fuse A Soft Start Fitted Sales invoice Bottom label Credit card receipt Customer survey form Bias meter Transformer Protection Upgrades HT delay fitted N A Output valves 1st Stag...

Page 3: ...Page 3 INSERTION OF VALVES IN MB150s DO NOT REPLACE OR CHANGE ROUND KT120 WITHOUT RE BIASING USE SUPPLIED METER DAMAGE AND POOR PERFORMANCE COULD RESULT USE ONLY KT120 KT150 and 6SN7 6N8P CV181 ...

Page 4: ...s to warm up and then push the standby switch into the down position You will hear a whumm sound The amplifier should now be working All valves should have a visible orange glow from the cathode heaters With the pre amp volume control set to minimum or nothing connected there should be no sound coming from the speakers except a barely discernable hum If there are any unpleasant sounds coming from ...

Page 5: ...n 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 se...

Page 6: ... help or Icon Audio Replacements should be 3 Amp anti surge The fuse in the wall plug should be a 3 or 5 amp fuse although unlikely to fail this should be checked if the amplifier fuse is OK No sound Have you selected the right input Is the Tape Monitor switch up Are all the connections OK Is everything switched on Are the speakers connected Distorted sound Could be your source the speakers or the...

Page 7: ...king the earth connection 3 Checking Bias You should get a reading of ideally 180mV if each valve is conducting correctly But variations from about 160mV to 200mV will have little effect Bear in mind that your mains voltage fluctuations can affect your readings by up to 10 So if all the valves are reading slightly high or slightly low this usually means this is due to your mains In this case no ad...

Page 8: ...e than a barely detectable hum from the speakers and the amplifier should sound OK when tested 6 If you cannot set up 180mv bias then the valve is probably faulty or is unsuitable if the reading is zero the individual fuse may be blown If the valves are brand new you will need to check again after approximately 10 100 hours after that only occasionally or if you suspect a problem 7 To avoid damage...

Page 9: ...guaranteed for commercial Public Address use or use in other situations The guarantee becomes void if the unit has been modified in any way not approved by Icon Audio 10 Packing Instructions It is essential that the original box and packing be kept in good condition as this provides vital protection during transit Please do not write on box but use removable labels Should the original box and pack...

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