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Passive Stereo
to Mono Resistive
Mixer
 These days the most
common audio format is two channel stereo, but there may be times when
we need to
convert this to one channel mono. Perhaps to feed the output of a
portable audio player such as a mobile phone into the input
of a mono guitar amplifier for example
 The
circuit is a standard combiner/splitter arrangement using 680 ohm
resistors, giving two identical
mono outputs from one stereo input. That's it really, but be
aware that as it uses fairly low value resistors, it cannot be
connected across an
existing stereo signal without reducing the stereo separation
of that signal. It should therefore be used on it's own dedicated audio
channel, or with an audio selector switch that isolates it from other
sources. Also being passive it will attenuate the signal slightly,
but it's
hardly noticable in practice
 It
can be assembled any way you want according to your needs, but I built
mine
as shown above, in a Hammond 1590 LLB
diecast box with four RCA chassis sockets mounted on the
lid in a square. The resistors simply go from the centre pin of
each
socket to a common point forming a
'star'. This
method of construction has the advantage of allowing any two sockets to
be the input
and
any two
to be the output. You can't go wrong!
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