As a Long Tail phase splitter, the gain from the non-inverting output will fall slightly below that of the inverting output. (The greater the value of the common cathode resistor, the smaller the discrepancy. But even if the cathode resistor is replaced with a constant current source, i.e. infinite impedance, the difference will not disappear, but only fall to the reciprocal of the amplification factor.)
    As a Differential amplifier, the gain from both outputs balances regardless of the value of the cathode resistor. A further advantage of the balanced input configuration is the effective increase in gain that derives from presenting each grid with its own input signal (roughly, twice that of the unbalanced input configuration).

   The Split Rail phase splitter's output impedance at its plate is extremely high, as the triode's rp is effectively increased by the mu times the cathode resistor value:
        rpī = rp + (mu + 1)Rk.
This rpī in parallel with the plate resistor defines the output impedance at the plate. Unfortunately, this large increase in effective rp undermines the triode's normally good PSRR figure in a circuit, as the voltage divider defined by the plate resistor and the rp now barely divides the noise present on the rail voltage.
   But in a circuit that uses a split rail power supply, the extremely high effective rp works to our advantage. Because the split rails contain anti-phase noise signals, this circuit can be tricked into exhibiting two low noise outputs.
   The trick is based on feeding the negative power supply rail noise into the Split Rail phase splitter's sole current path so that the noise from the positive power supply is cancelled at the plate by the addition of the negative rail noise.
   The implementation is simple enough: make the plate resistor equal to the cathode resistor and ensure that the noise at the bottom of the cathode resistor equals that of the negative power supply rail. This requires a second
bypassed cathode resistor to shift the DC points upward and allow DC level coupling of the input. Remember, this resistor is bypassed to the negative voltage rail and not ground.

Long Tail phase splitter    &    Differential amplifier

   What if the only source available is unbalanced? Well, then a Split Load phase splitter can be used to create a balanced input signal. Although this phase splitter is often derided, it definitely deserves a second and third look by anyone who wants to make the best use of tube circuits. Many of the accusations against this phase splitter are groundless, such as the claim that this phase splitter does not allow for the proper use of  feedback in an amplifier, and some of its actual failings, such as dissimilar output impedances and PSRR figures between phases, turn out to be real advantages in certain circuits.




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