Since the appearance of one of the main “Bestsellers” among audio frequency amplifiers - JLH1969, engineers have been thinking about creating output FETs for audio.
About 10 years have passed, and HITACHI has developed a complementary pair of output field-effect transistors 2SK134 / 2SJ49, for which it itself has developed a circuit.
The next generation of output transistors from HITACHI was a pair of 2SK1058 / 2SJ162, which has higher characteristics.
This amplifier, like the JLH1969, does not have the most "outstanding" performance as a result of measurements, however, the steady demand for the 2SK1058 / 2SJ162 output transistors and the HITACHI / Skritek circuit in particular suggests that this is a classic worthy of attention.
The module is easy to set up and requires only setting the quiescent current, depending on the supply voltage. The optimal quiescent current of the output stage is 120mA, which is approximately equal to 200mA for the power supply of the module as a whole. To adjust the quiescent current, the input is short-circuited, the ammeter is turned on in the gap of one of the supply arms and the required value is inserted using a trimming resistor on the board, after which we pause for 5-10 minutes. to warm up the radiator. You should focus on the acceptable temperature of the radiator (+ margin for a closed case). For a more accurate measurement of the quiescent current, an ammeter should be included in the gap of one of the sources of the output transistors, however, in this case, the module is automatically removed from the warranty, because this procedure requires the intervention of a soldering iron. On the other hand, accurate measurement of the quiescent current of output lateral transistors does not make sense, since these devices (transistors) are equipped with internal thermal stabilization elements.
For passive cooling at a supply voltage close to the maximum, a radiator of at least 750 sq. cm is required
Subjectively, the amplifier has a very pleasant sound with crystal clear highs and moderately pronounced mids.
The module can be recommended for building a high-quality power amplifier.