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This mod allows a complementary ganging of the tone control circuit to produce a "narrow" or "wide" audio
passband. Wide and narrow might well be called by the names often found on mid-20th Century shortwave radios;
"music" and "voice." By any other name, audio contouring helps adapt the audio passband to suit the material you
are listening to. If there is a lot of noise on the received signal, you can move the passband toward "narrow." If
you are enjoying a powerful foreign music station, you may want to make the passband "wide."
The "Passband" control does the same thing that the separate "bass" and "treble" controls do, but it consolidates
their utility for the ease of use - this also allows you to leave your bass and treble setting where you prefer them.
The mod requires that the tracks at "A", "B", "D", and "E" be cut so that the switch can be wired into the circuit.
Points "C" and "F" remain intact. Point "G" is discussed below.
At right, are the audio
passband contours that you
can expect from the mods.
The solid lines represent
the original circuit. The
dotted curve is the "voice"
response set at its
maximum. Likewise, the
dashed curve is the "music"
response, shown at max.
Of course, all curves may
be adjusted anywhere from
"flat" (0dB) to the maximum
settings shown. Also note
that all the curves are "level
normalized," meaning that
they have been shifted on
the plot to illustrate their
function - the chart is in
decibels, so all the
response curves are
relative to where you have
the volume control set.
If you are planning to make "air checks," then
this Audio Control mod is for you. This is just
basic audio console circuitry. Air checks are
recordings of off-air broadcasts. Commercial
radio stations do it as a matter of course.

The "pre" and "post outputs" allow you to set
up levels for your headphones (cue) and the
recording device (dub), independently.
The power amp level is then adjusted
accordingly for your monitor speaker system.
For playback, the "mute" switch is used to stop
radio audio and the recorder can be played
back through the SSR-III's audio system

Important Note: The SR-III's original
volume control is to be left intact. This will
be set up as a non-user control (Drive
Level adjust) and remain preset (at
approx 1/3 gain), inside the chassis of the
new SSR-III.