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High Performance Power Amplifier 400 Watt

400W High Performance Power Amplifier is designed to produce considerable power but still have low distortion. The sound quality on a power amplifier such as this are generally more dependent on the type of components used, PCB layout and wiring are good and certainly good design anyway.

Circuit diagram:
400W High Performance Power Amplifier circuit

In the differential used N-JFET that has very high input impedance (on foot Gate). N-JFET and are generally more resistant to RFI (Radio Frequency Interference) of the BJT, so that the amplifier is more secure than radio frequency interference on the input.

N-JFET which are type 2SK30A because it is relatively easy to obtain on the market and the price is not expensive and has low noise. N-JFET 2SK30A used must be coded "GR", this indicates the maximum capacity of the drain current is about 6mA for type GR. Because N-JFET 2SK30A only have an operating voltage up to -50V, then the (N-JFET) on differential parts need to be separated from the voltage supply (+ 63V). This is done by Q3 and Q4 that operate up to + 18V by Zener diode D1.

On the VAS (Q7) along Q8 form a cascode configuration. It aims to alleviate the VAS transistor (Q7) so as to decrease the distortion. Voltage Q7 Q8 detained by around 1,4V (2V {VLED} - 0,6V {VBEQ8}) by LED1. Now work Q7 (transconductance or I-V converter) lighter and Q8 are now working to channel (skip) voltage.

In the bootstrap added in the form of N-JFET Q10 to increase the bootstrap current regulations. N-JFET which are type 2SK30A. Because N-JFET 2SK30A have a low dissipation (max. 100mW @ Ta 25 ° C), the role of (value) R13 is very important. If R13 is too low, the Q10 will work at higher voltages, this can cause overheating and damaged Q10. If the value of R13 is too high then the Q10 would fail in improving the current regulatory bootstrap.

The ideal value for R13 is s.d 10k 12k with a power rating of 2W s.d 1W. R12 value is used to determine the magnitude of the drain current of about 4mA s.d 5mA Q10, R12 value depending on the character YFS (Forward transfer admittance) of Q10. But in general, for N-JFET 2SK30A-GR can be used values ​​between 100Ω 150Ω s.d ¼W.

At the output (final) used Compound Emitter-Follower configurations. The bias current is set around 50mA per output transistor.

Another interesting point is at the fuse (fuse) there is a resistor in parallel to the fuse. This resistor functions to hold temporarily (until charred and lost) in case one broke the fuse that may cause the DC voltage at the output. Also as a marker that is when the resistor is burnt and the smoke / odor that suggests us that the power amplifier should be turned off (Off). Value of about 100Ω ½W. This technique is commonly present in models of power amplifiers from Hugh Dean (AKSA).

Power Supply:
Recommendations for each of the Power Supply Power Amplifier with lowest load 4Ω use transformer 15A (to use two amplifiers 30A).
Use capacitor banks around 15.000μF / 80V per rail for the first amplifier (33.000μF / 80V per rail for 2 amplifier). If there are no capacitors 15000μF / 80V can be used three capacitors 4700μF / 80V in parallel, if diparalel value will approach the 15000μF. If there is no 80V voltage capacitor then use a higher voltage, for example 100V.
Diode bridge using a 35A per amplifier, for two amplifiers (stereo) we recommend using 2 diode bridge 35A in parallel, is to anticipate the damage (on the diode bridge and other equipment) that may occur in case of current shock which can cause damage to the diode bridge 35A.

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