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POSITIVE GROUND ON POWER AMPLIFIERS
On the latest versions of 105 amplifiers you will notice that we are fitting a red output plug to the
terminal marked negative and a black output plug to the terminal marked positive on the labels. The
only thing that has changed on the 105 in this connection is the markings on the labels. The 'live'
output terminal is still the terminal next to the fuse holder (hence the red plug as before). New
amplifiers are fully compatible with older ones, and, for correct phasing, the terminals nearest the
fuse holders are similar, and the terminals furthest from the fuse holders are "ground".
The reason for the alteration to the label is to comply with an ALSO (Active Loudspeaker Standards
Organisation) convention. Since the 105 is an inverting amplifier, the output terminal that
corresponds in phase to the input signal is in fact ground. This terminal must bear a '+' sign to meet
the Standard.
HEADPHONES, COMPARATORS ETC.
Keep all four terminals in a 105 stereo system discrete. Neither '+' nor '-' terminals should in any
circumstances be joined. Should you wish to use a headphone control box, please confirm that the
"earthy" sides of the two channels are kept separate. QED have confirmed that their headphone
control boxes are suitable in this matter. Do not feed the amplifiers into a loudspeaker
"COMPARATOR"
ELS LOUDSPEAKER
The only amplifier in our range which is suitable for driving the QUAD ELS is the 103. It is possible to
over-volt the loudspeaker with a 103D and of course with a 105.
Boothroyd Stuart
May 1980
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