Line level is more or less derived from 0dBmW on 600 Ohms. This is ~0.77V Vrms
or ~2.1Vpp balanced. Most consumer audio equipment will be overloaded with this
and require about 0.2Vpp to 0.5Vpp line level into 10 to 47kOhms. Most
professional audio equipment will accept 2.1Vpp input and often 600 Ohm balanced
circuits are used (with XLR 3-pin connectors and cables). The 1Vpp line level
'standard' comes from connecting a balanced 2.1Vpp line to burden resistors
(2x300 Ohms) and using the signal from one of them to feed a circuit, thus
making a balun. Of course the advantage of a balanced line is then lost.

The OP required low impedance drive so adding a buffer will be necessary. If
using LM386s then the signal from Olin's circuit would have to be attenuated
further before feeding the LM386s.

The OP's circuit with the continuous-running oscillator could also be used,
adding a simple switch to the audio path (where a volume potentiometer would
be). By switch I mean a CD4066 section or a CD4053 section. The 4053 can switch
the LM386 inputs from signal to ground and thus remove the residual oscillator
bleedthrough.

If this goes into a truck or bus with any kind of connection wire lengths where
other electrical equipment is used (like radios and lights) then transformers
will have to be used on each audio line to remove the ground loops.

Peter

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