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The Transcendent Patent



The series connected output stage is inherently unbalanced. The output signal is developed at the junction of the cathode of output tube V1 and the plate of output tube V2. The drive signal at the grid of V1 is in phase with the output. This causes degenerative feedback at V1. The cathode of V2 is at ground potential so its drive signal is not affected. A means is required to compensate for the degenerative feedback to provide equal drive signals to the output stage. The widely used Futterman technique is shown which attempts to solve the problem.

A conventional phase splitter is used to generate two out of phase signals which are required for any push-pull type output stage. The plate resistor of V3 is connected to a floating voltage regulator which is referenced to the output line. The regulator applies positive feedback, FB, to R1. The feedback is essentially the output signal. The drive signal for V1 is the summation of IN1 and FB as they are both in phase. This new signal has increased the amplitude of IN1 by the exact amount needed to compensate for the degenerative feedback of the output stage. The drive signal for V2, signal IN2, is equal to IN1. The problem of unbalanced drive signals appears to be solved.

There is a severe deficiency with this technique. The drive signal for V1 is increased in amplitude by the action of positive feedback. The drive signal for V2 is constrained to equal IN1 because tube V3 acts as a cathode follower at this junction. Feedback signal FB is applied to the entire phase splitter stage. Just as FB provides positive feedback to V1's drive signal, it applies negative feedback to the drive signal for V2. Positive feedback increases voltage gain and negative feedback reduces it. Forward voltage gain is therefore consumed at the cathode of V3. The drive signals through the system have unequal forward voltage gains. The signal amplitudes are correct, but the gains are not. The gain unbalance causes a DC offset in the output stage that is proportional to output level. The unbalance is responsible for the weak and feeble bass that these types of amplifiers produce in dynamic speakers even though measurements are quite good.

The Transcendent patent truly provides for equal forward voltage gains through the system. A floating unity gain buffer, X1, is referenced to the output line. This connection adds the correct amount of signal boost at the grid of V1 to overcome the affects of degenerative feedback in the output stage. No compensation is applied to the drive signal at V2 where it is not needed. Buffer X2 is required only for symmetry to equalize impedances and time constants. The voltage gains of the two drive signals are truly equal. This is verified by the absence of any DC offset in the output as the amplitude increases. In addition to dramatically improved bass performance, linearity is increased which reduces distortion and allows the output stage to be biased with a very low idle current reducing waste heat to levels approaching a conventional transformer coupled amplifier. The low heat and reduced stress on the tubes pushes reliability to very high levels. A direct coupled output is now possible making the highest levels of sonic performance a reality.
The patent is all encompassing and states the following in claim number 1:

"Means for compensating for said degeneration including means for providing said output signal as a voltage reference for said first intermediate unity gain section so that said output signal is superimposed only on said first intermediate signal thereby compensating for said degeneration."