FET voltage control devices for its high-frequency characteristics, and as a tube amplifier tube-like sound. I have produced a partial negative feedback FET amplifier, the actual effect of listening is not satisfactory. Designed as a negative feedback loop amplifier, the sweet sounds markedly effective, treble detail, the intensity of the full bass, outstanding results.
Principles:
Circuit principle as shown below, for a typical OCL amp. IC1-A for the input stage; BG1, BG2 incentive for the class; BG3, BG4 is composed of complementary MOSFET output level; IC1-B for the DC Circuit 0.1 Servo.
IC1-A voltage from the amplification, because of limited supply voltage, the level output signal range of not more than ± 15V, if the after-use of the radio output, output power too small.
The circuit is designed to play Yun-simple, excellent performance characteristics, but also meet the appropriate output power. Therefore, the power circuit from the two groups (± 15V, ± 36V) power supply, regulators ± 15V supply Yun-use, ± 36V supply after-use. BG1, BG2 for a total emitter circuit, R8, R9 for the negative feedback resistor, R1, R5, D1, D2, R18, R19 for BG1, BG2 provide a stable DC bias, in order to ensure its on-state, in addition to the same level Voltage amplification, the more important is to achieve a different power supply circuit signal coupling. FET voltage amplifier is the case, although the current drive did not specifically require, but to consider FET input capacitance of the characteristics of high-frequency.
Therefore, the resistance of the drive signal should be small enough. BG3, BG4 signal the driver were taken from the BG2, BG1 load R4, R3. BG1, BG2 the collector load resistance was divided into two sections, as the source of FET gate drive voltage should be no larger than 20 volts. BG3, BG4 for MOSFET on the composition of the drain output stage. R11, R12 for the source of negative feedback resistor. IC1-B's role is stable at the end of the mid-point of DC voltage, in order to achieve the DC amplifier. R13, R7 is a negative feedback loop resistance. R20, R21 to prevent the MOS high frequency of self-designed; C2, R16 role is to prevent self-circuit.
Second, installation and commissioning:
IC1, BG1 ~ BG4 principle of choice as shown in the device can also be optional parameters similar to the device. BG1, BG2 request β value greater than 100, Vceo greater than 100 V, Icm more than 1 A, Pcm more than 10 W; BG3, BG4 parameters for the VDSS = 140V; ID = 8A; PD = 100W. To the extent possible, all of the complementary pair. Resistance R2, R3, R4, R10, R16 optional 1 W Metal Film, R11, R12 optional 3 W resistance, resistance to other optional 1 / 4 W Wuhuan resistance. R20, R21 should be installed as close as possible to the MOS gate. You Zhipin capacitor selection.
Static accurate detection, connect the power to detect whether the midpoint voltage to zero volts; measurement BG3, BG4 gate-source voltage, usually about 1 V. To be pure A Larger, more R18, R19 resistance. To connect all the normal speakers, audio test machine.
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