fed a mono signal, as the image always seems wider and less spatially specified. Why? Some of the blame must lie in the disparity between loudspeakers, differences in frequency response, mismatching in crossover components, and different room reflections. And certainly some of the blame must lie in the disparity between linestage and power amplifier channels.
     Expanding the width requires cross feeding an inverted phase signal from the opposing channel (ultimately, this signal should be frequency selective). A 100% ratio will completely eliminate the signal common to both channels, resulting in a extreme separation of instruments, so extreme that some instruments will appear far to the outside of the speakers.
    A reasonable amount of constriction and expansion might at the 50% mark for both adding and subtracting one channel from the other. How do implement such a control?
     Starting with the blending into mono direction, the plan is simple: place a varying amount of resistance between the plates of two grounded-cathode amplifiers. The smaller the resistance, the greater the blend. Hitting the 50% mark requires that the bleed resistor equal the rp in parallel with the plate resistor in a grounded-cathode amplifier with a bypassed cathode resistor.

      (One great advantage the turntable held over the CD player was the turntable's allowing some sonic adjustment. Increase the VTA and the sound becomes more aggressive; loosen the cabling and the sound becomes defuse. The problem here is that the adjustment is not easy.)
   Let's be honest: much of the stereo gear and accessories made are no more than un-adjustable tone controls. We choose a certain patch cord that lessens the sizzle from the tweeters. We buy oil-coupling capacitors to undo the harsh artifacts of modern recordings. And there is nothing wrong with these practices other than they are not very flexible, as different songs on the same album often require different sonic antidotes. Changing coupling capacitors per song is too much to ask. Even changing a knob's setting per song is asking too much. (Once a twelve-knob linestage is created, the best addition would be a microprocessor that would keep track of each track and automatically apply the last used settings for that track.)
   
Making the Sonic Controls Work
      Each sonic control requires making some change to the circuit. It might be as little as increasing or decreasing                        the idle current. Or it might be as complex as switching types of tubes or even circuit topologies. Switching between different coupling capacitors and plate resistors  might be needed. Varying the amount of feedback while co-varying the input signal might also be useful in certain sonic controls. The hard part is correlating the desired sonic signature with some aspect of the circuit that can be switched in and out of the circuit. Only a few of the controls can be presently implemented, as our ignorance of the psychoacoustics behind the perceived sonics and electronic circuits is depressingly vast.

Width Control: Narrow and Wide
    Combing the left and the right audio signals into one narrows the sonic stage width by creating a mono signal. Interestingly, the result seldom sounds like a single loudspeaker being

      But the cathode resistor should be left unbypassed, as an unconstrained cathode will be needed to implement the broadening of the signal. With the unbypassed cathode resistor, the resistor value for 50% must equal:

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