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CDT-100
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PST-100

The Ypsilon PST-100 Preamplifier

Most manufacturers develop a circuit for their power amplifier and then use the design for their preamplifier. The raison d’etre of a power amplifier is to amplify the signal and drive the loudspeakers. That of a line preamplifier is to draw together the various source components; to attenuate the signal in order to achieve "volume control"; to have low enough output impedance in order to drive the cables; and finally, to provide gain if it is required. It performs totally different duties to those of a power amplifier and needs to be designed in a totally different manner.

Conventional wisdom suggests that the most critical part of a preamplifier is the active circuit design. Ypsilon, however, believe that the means of signal attenuation (the volume control) is the most critical to the overall sound of a preamplifier. Most designers use resistor attenuators for volume control. Ypsilon themselves have used resistor attenuators with high quality resistors (Vishay, Holco, tantalum types etc.) in the past, but that was before they developed a very special transformer as the means of attenuation. It was immediately apparent just how grainy and discontinuous resistors sound, even the best of them. The short explanation of this observation is that the series resistor transforms the constant voltage into current and the parallel resistor the constant current into voltage. The materials used in resistors are far from ideal as conductors- they sound much worse than pure copper or silver- and they do a lot of harm to the signal, since it has to be more or less re-constructed depending on the properties of the resistor.

 

In a transformer, however, the magnetic circuit can be ultra linear when the very best core materials are used. The sound of such materials is much more musical and detailed compared with the best resistors. So Ypsilon produced, in-house, a special transformer attenuator with 31 taps of 1.5 db each using a special winding technique, which takes a week for one of the designers to accomplish by hand, using special winding techniques The special core material is at the cutting edge of what is possible to achieve. The only drawback with using the transformer attenuator is that it is very expensive and difficult to manufacture with such small tolerances.


The PST-100 operates in two modes, either completely passive (for systems that do not require additional gain- for example the Ypsilon VS amplifier) or active. Both modes use the same special transformer attenuator. The active gain stage is based on a single triode, using zero feedback and is coupled to the bespoke transformer. It is perfectly executed. Copper foil, the use of paper in oil signal capacitors, valve rectification and choke regulation of the power supply, with custom made pure silver wire, is the ideal environment for the triode to perform at its best. Instead of using the attenuator at the input and then the active gain stage, transformer coupled, Ypsilon designed the attenuator in such a way that it could be placed at the output as the output transformer. It doesn’t get any simpler than that. With a short signal path: one triode, one transformer, they achieved a maximum gain of 12db, output impedance of 150 ohms and maximum attenuation of 52 db.

 

        BANDWIDTH                     5 Hz- 100 KHz -3db
        OUTPUT RESISTANCE        150 Ohm
        INPUT RESISTANCE           50 Kohm
        GAIN                                x10 (20db)
        DIMENSIONS                    400x180x410 (WxHxD) mm
        POWER CONSUMPTION      150 Va maximum
        WEIGHT                            25 Kg
       

 

 

 

 

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