Download 6.0 SD II Final Documentation

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Fig. 3.2.4.8. Audio Preamplifier with an inverting gain of 100. Notice the
added film capacitors for stability. The 1uF output capacitor acts as a
coupling capacitor between this circuit and the mixer.
As it can be seen in Fig.3.2.4.8, the preamplifier inverts the instrument input. The
C1 0.22 uF capacitor will filter the DC component of the input. The manufacturer
recommends the capacitor in the feedback path for added stability to the circuit.
Both the input and feedback capacitors are film types due to their reduced noise
figure in the audio band.
Baxandall Tone Control
The Baxandall tone control topology is available in passive and active
configurations. Previous experimentation by the team with the passive Baxandall
circuits did not deliver expected results so an active Baxandall topology was
favored. The one obvious difference between the passive and the active
implementations of the baxandall filters are that the active configuration can
actually deliver gain. Careful consideration must be put in picking the values of
the baxandall circuitry so that the user does not clip the audio signal because of
too much envelope shaping with the equalizers. The total gain of the Baxandall
circuit will be limited to +/- 6 dB of amplification or cut. The active baxandall
topology for the actual design can be appreciated in figure 3.2.4.9.
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