If your audio tones are working in reverse your vco is set up wrong some how.
Have you tried this ? VRI provides a
means of unbalancing the circuit to allow the output to be set
manually. This is used to set up the detector in operation to
produce an audio signal to the preferred pitch.
Go over your Audio circuit.
AUDIO
The final part of the circuit is the audio oscillator
section, this is a conventional 555 circuit except that
the charge circuit for the capacitor C12 is not a
resistor but a transistor TR5. TR5 is driven from the
peak detector TR4 via a low pass filter consisting of
R21 and C11.
Large pulses cause TR5 to turn on more and so
C12 charges more quickly and the output pitch rises.
This arrangement is at its most sensitive for the
lowest pulse levels and so provides the ideal
characteristic for sensitivity.
The output from IC5 is fed directly to a pair of
personal stereo headphones via C14 and R25. The
two earpieces can be connected in series by
connecting to the tip and ring connections of the
phones. This is more efficient than parallel
connection and although the earpieces are then
connected in antiphase this does not seem to matter
in this type of application.
HH Homefire
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