Core-Amps

Technical

The tube output stages have the following disadvantages
1: The good output tubes are very expensive and have a short limit of life.
2: Their sound behavior mainly depends on the quality of the output transformer which is an electromagnetic converter.It converts the primary electric field to magnetic field and vice-versa, the magnetic field to electric field in the secondary winding. This transformation from one form of energy to the other and vice-versa is very natural to bring into the sound signal and other harmonics which have nothing to do with the signal, mainly because of the hysteresis loop of the iron core. Because of the hysteresis loop the current waveform in the secondary winding of the output transformer doesn’t follow the voltage waveform. This means harmonic distortion in the signal which comes to the speakers. There are manufacturers who advertise the exotic iron cores of their output transformers, for having hysteresis loop which have almost zero area. This area may be trivial but it continues to exist. Apart of this all these are very expensive materials. It’s not only the hysteresis loop of the core which influences the sound signal at the output of the transformer but also the capacitance among the windings, the primary inductance, the leakage inductance etc. The transistor output stages don’t have the previous problems. The reason that the transistor amplifiers don’t have a pleasant sound is not because of the output stage but the voltage amplification stage. The transistor, as a voltage amplifier, has disadvantages against the tube as it is a non linear element. To eliminate the distortions, which are created at the voltage amplification stages, the manufacturers design these stages with very high amplification, many thousand times, and applies very high negative feedback to eliminate the total amplification of the amplifier to the desirable level, trying to eliminate and the total distortion of the amplifier. However, eliminating the total distortion with high negative feedback, they create very bad effects on the ear. This is the reason why the transistor amplifiers don’t sound very pleasant. A hybrid design matches only the advantages of the amplifiers mentioned above without having disadvantages, on the condition that it has been correctly designed. And saying hybrid design I mean that the voltage amplification is achieved with tubes and the output stage is with transistor and not the reverse. And, of course, it must have not total negative feedback. The total negative feedback is a discovery that has to do only with good measurements but it destroys everything that has to do with the correct sound.