Design Goals
After two RIAA phono stages, a line stage should come in handy. This line stage uses the same Constant Current Draw Grounded Cathode (CCDGC) amplifier topology as last month's phono stage, but with a twist. But before examining the schematic, consider the purpose and design goals of a line stage. Simply put, a line stage is needed either to boast a weak signal voltage up to a signal voltage sufficient to drive a power amplifier to full output, or to deliver current sufficient to drive a high capacitance load (such as long stretches of interconnect).

1.  Just how much gain is needed for a line amplifier?
Let's begin the answer with the observation that most line amplifiers have too much gain. Working on the assumption that even the world's most inefficient power amplifier needs only 3 volts of drive signal to be driven to full output and even the weakest tape deck or CD player puts out at least 1/2 v of signal, the greatest amount of gain needed would be 6:1 or 15 dB of gain. Yet most tube line stages have between 20 to 30 dB of gain (10:1 to 32:1). While this extra gain impresses the audio neophyte who marvels at the power implicit in the distorted thunder that a mere one quarter twist of the volume knob provokes, it ultimately only subtracts from the useful range of turn on the volume and usually

only worsens the signal-to-noise ratio of the line stage. (Remember, many audio systems don't use an active gain line stage at all (zero gain) and rely on only passive attenuators and switches to connect line level components to the power amplifier. If 20 to 30 dB of gain is too much, how much then is best? The answer will depend on each system. (This is the answer most hated by dogmatic audiophiles who seek absolute answers to relative questions... Yeah, just what is THE best coupling cap? What is THE perfect value for all grid stopper resistors?) A safe guess, however, would be 10 to 20 dB of gain, which translates into 3 to 10 times the input signal.

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