Key issues in the process of making household single ended field-effect transistors

1. Power circuit

Due to the PASS ZEN1 amplifier operating in a single ended Class A state, the static current during dual channel operation is approximately 4 A. If a single transformer is used for power supply, the transformer capacity and secondary wire diameter must be relatively large. Otherwise, using independent power supply for each channel is a good choice. This machine uses one 500W ring bull as dual channel power supply; Due to the large static current, the capacity and quality of the rectifier bridge must be guaranteed. A 50A rectifier bridge should be selected for dual channel power supply, otherwise the voltage drop will be too large, and the rectifier bridge will seriously heat up or even burn out. The power supply voltage should be ensured to be around 34 V; At the same time, due to the heavy load on the power circuit, the filtering capacitor must have sufficient capacity, otherwise it may cause AC noise. If it is difficult to eliminate AC noise without using a stable power supply, a simple RC filtering form can be used, and the effect is also good. At this time, R should use a resistor with a resistance value of less than 0.1 Ω and adopt a multi-stage filtering form.

2. Amplification circuit debugging

The static operating current of PASS ZEN1 is set by R1. Increasing R1 appropriately can further reduce power consumption, but at the same time, the maximum output power of the machine also decreases. When the area of the heat sink is relatively small, the above method can be used to compromise, but it is generally not recommended to do so.

When the circuit connection is correct, power on the machine, measure the voltage between pins S and D of Q1, and adjust P1 so that the voltage between pins S and D is half of the supply voltage.

3. Machine tone tuning

The devices that have a significant impact on the sound quality of this amplifier are mainly IRFP140 and output capacitors C3 and C4. The capacitors should be selected as audio specific capacitors as much as possible. At the same time, one 6800 uF capacitor can be used in parallel with one 1 uF CBB capacitor instead of C3 and C4.

 4. The heat dissipation of the machine and the fixation of the power pipe

 Due to the high heat generation of Class A machines, large external radiators or forced air cooling should be used. The power diode can be directly fixed on the heat sink. Due to the high temperature of the heat sink, the circuit board should be slightly away from the heat sink and connected to the power diode through wires.

 PASS ZEN1 is a pure back-end amplifier with a small gain, which needs to be connected to a front-end amplifier before it can be connected to CD and other players. If there is no front stage, a homemade front stage can be made using the junction field-effect transistor 2SK30. Due to 2SK30 being a depletion type field-effect transistor, the bias circuit becomes simpler, considering the use of PASS ZEN1 power supply.

 At this point, a single ended field-effect transistor amplifier with rich electronic diode sound has been produced. The circuit is simple, the sound is balanced, and the resolution is also quite good.