TABLE OF CONTENTS The pre-amplifier receives a variety of signals at different levels, processes them, and passes them to the power amplifier. It should do this without adding noticeable noise or distortion and should be convenient to use.
The block diagram of a typical pre-amplifier is shown in Fig. 7.1.
Working back from the output, we have a line stage which provides a limited amount of gain; it may be designed to drive long cables, and it may even include tone controls. This is preceded by the volume control and input selector. One of the sources to the selector switch is an RIAA equalized disc stage, although many modern pre-amplifiers neglect this stage because it is so difficult to design. The excuse for this is that the LP is obsolete. This may be so, but there are many irreplaceable recordings on LPs that need to be played, so a comprehensive pre-amplifier should include a disc stage.
The pre-amplifier has to provide only a very limited output voltage to the power amplifier, as even the most insensitive power amplifiers do not require more than 4 or 5 V RMS to drive them into clipping. This means that we are concerned only with linearity and not headroom in this stage. The stage must drive the capacitance of the cable without excessive loss at high frequencies, and it may need to be able to drive power amplifiers of lower input impedance, such...
