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Leak Stereo 20 stereo power amplifier |
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I AM often asked which amplifiers do I find the most interesting, those made by old-established firms or those made by newcomers to Hi-Fi? This is a difficult question to answer. In general I suppose I would find the unknown quantity of greater interest. A much easier question to answer would be, which amplifiers do I find most pleasant to use? Certainly Leak would be somewhere near the top of the list. Leak amplifiers are always a joy to handle, not only because of the high standard of performance but because of their superb workmanship and attention to detail. Here is an example: The "Stereo 20" is not only fitted with 2 extra mains sockets for gramophone motor etc., but the plugs and 2 mains leads are supplied as well. A small point perhaps, but it does simplify installation--especially for the novice. The Leak "Point one" stereo preamplifier was released late last year and is basically the twin-channel version of the popular "Point One" control unit. Although it is primarily intended for use with the "Stereo 20” or "Stereo 50", it can be used with any two amplifiers such as the TL/12, TL/15, TL/50 plus etc. The "Stereo 20" which was actually supplied with the preamplifier is essentially two 10-watt amplifiers similar to the TL/12 plus mounted on one fairly large chassis with the power supply. Grain oriented steel is used for mains and output transformers. Circuit Details Each channel of the power amplifier comprises a triode stage, which is coupled to a cathode-coupled phase splitter, and an Ultra-linear output stage using 2 EL84s. The only difference from the standard Leak amplifiers is the use of a triode input stage instead of a pentode. RC smoothing is used and the common rectifier is a GZ34.
One recording characteristic is provided as shown in the diagram and CCIR 7½ ips compensation is given when playing direct from tape heads. NARTB and other characteristics can be obtained by adjusting the tone controls. The Tone Controls gave a lift of 17dB and cut of I5dB at 40 c/s with a lift of 12dB and cut of 16dB at 9 kc/c. No low-pass filter either fixed or variable is provided. The rumble filter, which is switched, attenuated from about 100 c/s with a 3dB point at 70 c/s and gives a cut-off of 13.5dB at 20 c/s. Crosstalk between channels varied from -30dB at 10 Kc/s to -54dB at 1,000 c/s. Matching was in general within 1dB for all settings of the controls. The balance control is ganged and either channel can be faded to zero without affecting the other.
G.W.T.
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