Nvarcher A Pair BA15MKII 150W power amplifier board based on KRELL KSA100 improved version marine amplifier Audio Amplifier Boards

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Size 300*97MM,


There is a UPC1237 speaker protection circuit on the circuit, plus a complete switch delay and midpoint protection circuit. Very high signal-to-noise ratio requires dual mono independent power supply. It can be used for 50W pure Class A or 200W Class A and B amplification. The supply voltage can work in the range of +-35V to +-70V. It is recommended to use the front high and the low power supply, the voltage level is 6-12V higher than the current level, and the voltage amplifying level is stable.

2. BA-15KMII input adopts FET diamond diamond differential circuit. JFET uses K246/J103, upper tube uses 992/1845, and each tube's working current is 1.8-2MA. Main voltage amplifier stage: use KRELL's improved Esoteric A-100 circuit: Darlington connection emitter plus constant current source collector grounded push-pull amplifier circuit. (With the addition of the constant current source, the whole machine has better low frequency control and more delicate sound. Friends who play KRELL circuit can try it again. After adding the constant current source, the voltage should be increased by 5-10V.) Take its common circuit The output internal resistance is low, which can greatly improve the linearity of the voltage amplifier stage. The front tube can use a larger current to further charge and discharge the junction capacitance of the main amplifier tube, which greatly improves the high-frequency characteristics. The front tube (Q9Q10 ) With C2705/A1145, the working current is 5.6MA, and the rear tube is available with C5171/A1930 current of 18MA. Due to the high voltage and large current of this stage, the static power consumption is about 1.5W, so a larger radiator must be added. The constant current source uses a matched E562 constant current tube. Tested: This circuit has both the common emission circuit of the golden voice or the high frequency transparency of the ground amplifier circuit of Harvin Carden and the common collection push circuit of KRELL (Darlington connection). The medium and low frequency are thick. The characteristic does not have the shortcomings of the relatively thin intermediate frequency of the golden voice circuit and the relatively poor control of the low frequency and the relatively incomplete high frequency of the KRELL circuit. The disadvantage is that the voltage of the front tube needs to be increased by 5-10V after the constant current source is added, and the power supply circuit is more complicated.

3. Current amplification stage: Generally, the final stage of high-power machines with 150W/8R usually uses level 3 Darlington. The current amplification ability of level 3 Darlington is strong, and the extension of high and low frequencies is good, but the disadvantage is that it uses more tubes. If it is not done well, the stability will be poor. The extension of level 2 Darlington is not as good as level 3 relative to the high and low frequencies, but the circuit will be more stable and the density of the intermediate frequency will be better. There is less one pair of tubes, which reduces the difficulty of production. This circuit uses two-stage Darlington to compensate for the insufficient current amplification of the two-stage Darlington by increasing the current of the driver stage, and the quiescent current of the voltage amplifier stage of this circuit is 20MA, which further compensates for the second-stage Darlington insufficient. In this way, the level 2 Darlington can completely drive four pairs of high-power tubes, as long as the power supply is sufficient, it can output 200W/8R, 400W/4R. At this level of the drive tube (Q13Q14) 5171/1930 working current is 30MA, the current level is four pairs of 2SA1386A 2SC3519A, each tube current is 186MA.

4: Mid-point zeroing and feedback circuit: Mid-point zeroing does not use active servos. It is afraid of complexity, and second, it is afraid that it will affect the sound if it is not done well (this may be my psychological effect), and there is no ordinary input stage. The S pole or the emitter of the main voltage amplifier stage plus a fine adjustment to zero. Instead, learn the circuit of KAS100 to add more, R39, R40, R41, D1, D2, and other components for midpoint zero adjustment. The advantage of adding more components is: to achieve DC balance while not destroying the AC balance of the circuit .

The V1 board is a large tube without recesses, and the high-current wiring will be thicker. It can only be installed in a chassis with an inner height of 160mm. The bias tube is between the two large tubes.

The large tube of the V2 board is concave, and the board can be installed in a cabinet with a height of 145Mm. The offset tube is between the push tube and the large tube. No other difference