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There are two schools of thought with regard to the method by which an audio signal should be amplified, that is to say solid State and Vacuum Tubes.Ypsilon came to the conclusion that the real question was not Solid State versus Vacuum Tubes, but Single-ended versus Push-Pull amplification topology.



In Push-Pull (P-P) class A and class AB, two (or bank of parallel) active components are used, where one sinks current and the other sources current. In class AB operation the problem is that crossover distortion produces a cold and harsh sound. In class A operation, the two halves are not the same component (PNP with NPN transistor or P-channel with N-channel mosfet). In quasi-complementary topology, where two of the same components are used in the two halves, a problem arises from the different topology, for example one half NPN transistor common emitter, the other half common collector. To minimize distortion various topologies have been used with different types of feedback. E.g. voltage feedback, current feedback, nested feedback/error correction. This approach only leads down a one way path to lifeless music.
Even when there are two same halves in a Class A pentode or a triode P-P amplifier, the sound is not as convincingly natural. This happens because one half acts somewhat as an "active" current source to the other half and thus loading each other, leading to a mechanical sound. An additional problem is the phase-splitter stage. It is not possible to achieve consistency with active devices and therefore the conclusion must be that P-P is not the way forward for achieving the best in musical reproduction.



In single-ended amplification (SE), only one (or bank of parallel) active component is used. This demands operation in Class A, where current flows independently of the audio signal. In general, SE amplifiers are low wattage, tube amplifiers. They provide musical involvement when properly designed and executed. The most commonly used output tubes are 211, 845 and 833. The big drawback with these tubes is that, in order to achieve maximum available power, they have to be driven in class A2 (Grid starts to draw current from the previous stage). The result is a difficult and awkward load for the driver stage, resulting in a loss of linearity. For example, the  211 in pure class A delivers about 12 watts, after this and up to 25-30 watts,it starts to draw up to 30-50mA. The load that the driver stage sees is not constant during the full sine wave.

Neither is parallel multiple tubes a solution, because each tube loads the other inconsistently due to differences between the tubes, which no amount of matching can overcome. This topology produces an edgy, unmusical sound, perhaps a result of the measured distortion containing a high proportion of odd order harmonics (3rd, 5th, and 7th).



-Output impedance: Without feedback, this will normally be more than 1.5-2 ohms. An amplifier will alter its frequency response in loudspeakers with big dips and peaks in the impedance curve, thereby changing the tonal accuracy of the loudspeaker.

-Feedback: All types that are returning from the output of one stage to a previous one destroy the musical experience. Feedback is trying to correct something that has already happened. The more you include in the feedback loop the worse the circuit sounds. In general, it is the most unnatural technique used in designing amplifiers.

-Followers: A circuit topology meaning Emitter follower or Cathode follower or Source follower. It is a topology that provides gain nearly times one. This is a 100% feedback topology. A cold sound and flat image. Instruments don't float in space.

-Symmetrical: one half sees the other as a load. Theoretically it is not a contributing load since it is too high, but it compresses and distorts the images' depth. Also symmetrical topologies lead to clinical sound.

-Balanced (or bridged): Meaning two amplifiers working in antiphase, meaning that two amplifiers are
in series with the signal. Double the problem! This topology is supposed to cancel second order       harmonic distortion. It does, however, nothing for 3rd, 5th, 7th.

-Differential amplifier: The majority of solid-state amplifiers use at the input a differential amplifier, as the
first stage. Usually, the feedback is returned to one leg or sometimes both legs are used as plus and minus inputs. In effect, one leg operates as a follower driving the other half.

-Very low output impedance: We often hear that an amplifier has very good driving capabilities because it provides very low output impedance. Although it is good to have low enough output impedance in order not to alter frequency response of the loudspeakers, lowering output impedance further means more feedback in one way or another, regardless of circuit topology. Some claim a no-feedback design with 0,1 ohm output impedance. This most probably means there is an emitter (or source) follower at the output: 100% feedback.



Single-ended amplification provides something that no P-P ever can. It is closer to the "real thing”. Music flows in a way that happens only in live performances. By incorporating a unique single-ended mosfet output stage, or the highly linear GM70 valve in the VS, Ypsilon achieves all the virtues of a big Single-ended triode output stage without having its drawbacks. The design produces more power, drive, transparency and musical involvement. Without using overall feedback, the Ypsilon SET100 achieves output power of 100watts and in the case of the VS 40 watts; enough gain, and sufficiently low output impedance. These amplifiers reproduce music with a natural scale; they bring the listener closer to the performance, to be touched and overwhelmed probably for the first time; all because the Ypsilon electronics bring a greater understanding and response to what the composer or song writer intended to convey to his audience.



Tel: 07799812271 - E-mail: glyn@amadeus-audio.co.uk
1 Hoewood, Millglade, Small Dole, West Sussex