The design of the present
amplifier is a mixture of these. The result is a unit that does not use esoteric components, is not too complex, and is fairly easily reproduced.
There will be a few eyebrows raised at the power output of 300 watts (into 4Ohm) it is true, of course, that in the average living room 30–40 W per channel is more than sufficient. However, peaks in the reproduced music may have a power of 10–20 times the average level. This means that some reserve power is desirable. Also, there are loudspeakers around with such a low efficiency that a lot more than 30–40W is needed.
the higher than usual supply voltage and the presence of a couple of ics. The first is to be expected in view of the power output. One of the ics is not in the signal path and this immediately points to it being part of a protection circuit. What is unconventional is an IC in the input stage. Normally, this stage consists of a differential amplifier followed by a voltage amplifier of sorts, often also a differential amplifier, to drive the predriver stages.
Circuit Amplifier MJ15004 and MJ15003
The internal circuit of IC1 is shown in the box on further on in this article. It may also be of interest to note that the NE5534 is found in nine out of every ten cd players This is reflected in its price which is low. Its only drawback is that its supply voltage is far below that of the remainder of the amplifier.
This means an additional symmetrical supply of ±15 V. Moreover, it restricts the drive capability of the input stage. The
supply requirement is easily met with the aid of a couple of zener diodes and resistors.
Conventional power amplifier with high-pass and low-pass filter. Supplied 60V DC, this circuit can produce about 300W sound power. Opamp NE5534 is arranged as a differential amplifier, output of NE5534 is applied to drive stages MJE340 and MJE350 via R6 from pin 6. The output amplifier proper consists of drive stages MJE1530 and MJE1531 and power transistors pairs of MJ15003 and pairs of MJ15004, which have been arranged as symmetrical power darlingtons.