Over the past 50 years, progress in the electronics industry has come a long way. But the same cannot be said about the technique for reproducing sound. For almost a hundred years since the invention of an electronic amplifying device - a lamp, followed by a transistor, it suddenly became clear that simple circuit solutions that have been known for many years have the best sound. And for some reason, no modern technological sophistication improves the sound quality.
The JLH amplifier design was born at a time when the era of tube amplifiers was nearing its end, transistors rapidly replacing vacuum devices in almost all areas of electronics. Sound technology did not escape this fate. Engineers began to design transistor amplifiers with an eye first of all on the parameters: high output power and extremely low distortion. Their designs were for the most part extremely complex and differed from tube circuits by the use of numerous and deep feedbacks. And this, as it turned out later, did not add any quality to the sound.
The whole ideology of building an amplifier by John Lee Hood is subject to the idea of ​​​​minimalism, there is nothing superfluous in it ...
The module almost completely corresponds to the original JLH1969 scheme, redesigned for a modern element base. The use of original and high-quality components allows you to achieve the very “live” sound for which this amplifier is valued. The difference between this particular module and similar solutions is the thoughtful topology of the printed circuit board plus minor improvements designed to reduce the influence of the power supply on the output noise level. Thus, the module is adapted to work with an unstabilized power supply, when working with which, the background in the acoustics is completely absent. All resistors are metal-film, 1W, which adds reliability to the device.
Setting up the amplifier is very simple and boils down to:
1. Adjusting the quiescent current (recommended about 1.2A) using the “quiescent current” multi-turn potentiometer, while the input must be closed;
2. Adjusting the output voltage (up to the output capacitor), the required value is equal to half the supply voltage. It is set with a multi-turn potentiometer “output voltage”. A more precise adjustment can be made using an oscilloscope by introducing the amplifier into a small clipping and using a trimming potentiometer, achieving maximum symmetry of cutting off the positive and negative half-waves.
After adjusting the quiescent current, when assembling a complete, stationary amplifier, you can increase the level of reliability by replacing the trimmer potentiometer with a 1W resistor with an equivalent resistance. Under this resistor there is a place on the printed circuit board next to the potentiometer and signed "180/560 / 1.2"
For passive cooling at a supply voltage close to the maximum, a radiator of at least 2000 sq. cm is required
The amplifier sounds very natural and transparent at any volume within 10 watts of its power.
The module can be recommended for building a high-quality low power amplifier, as well as for getting acquainted with the "pure" and "classic" class A.
The amplifier is assembled on 2 quasi-complementary output transistors 2SC5200 TOSHIBA
Under the order, it is possible to assemble this amplifier with the following output transistors:
TTC5200 - TOSHIBA
2SC3281 - TOSHIBA (Dismantling, various batches)
MJL21194 - MOTOROLA
FJL4315 - MOTOROLA
NJW0281 - MOTOROLA