Here's a Leach Amplifier based on 2SC5200 and 2SA1943 output power transistors that can provide up to 700W of power. The mechanical design is relatively simple, the transistors are placed on the two cooling profiles with a height of 66 mm, width 44mm, overall length 260mm. They are turned against each other Thus, from the cooling tunnel. Coolers are attaching the nylon backing which allows the assembly of transistors without washers, and thus better transfer of heat. DPS amplifier is at the top of the tunnel and the transistors are soldered from the bottom of PCB.
Adjust the amplifier power 700W looks easy, but we must not forget that the change in forcing transistors, the entire re-engagement of frequency offset. It is necessary to modify the current insurance policy which serves to protect the final transistors. Their tendency to be allowed to keep the transistors in the SOAR characteristics. First it was necessary to calculate all the necessary resistors and then measured to verify the accuracy of the calculations, it is managed with satisfactory results.
Peripheral changes needed for it to be able to consistently amplifier to supply power.
- First you need to replace the 2k2 resistors in series with the LEDs at Zenerovými resistors with higher wattage. Suffice 1/2W resistors, power loss at 80V +-based 1W.
- Then was traded 1k2 resistor in the feedback resistor at 620 ohms. Which is the original gain has doubled, so now is the overall gain amplifier 40 and the maximum excitation is sufficient to 1V rms.
- Předbudiči transistors were replaced by stronger MJE15032/33 because KF467/470 are allowed collector current 20mA
- At the exciter output stages are used the same transistors as the output stage.
- Number of terminals of transistors has been increased to eight pairs
- It had to occur to compensate for the excitation level by adding a capacitor 10pF to 47pF + 22K member. This led to a slight "slow" amplifiers, but this did not affect the resulting parameters. This capacity is tuned precisely for this type of terminal transistors 2SA1943/2SC5200. With that it is a minimum value at which the amplifier operates stably without overshoot at the rising and falling edges of the square.
- The last adjustment, the adjustment terminal current protection transistor. The SOAR transistor characteristics shows that the maximum allowable collector current when the voltage of 1.5 A is ideal for cooling, so it's actually less. Therefore, the current protection is set to 12A, single-arm. This copy protection SOAR transistor characteristics. Short-circuit current is about 6 A which is about 075A per transistor. This is far below the SOAR characteristics.
The mechanical design is relatively simple, the transistors are placed on the two cooling profiles with a height of 66 mm, width 44mm, overall length 260mm. They are turned against each other Thus, from the cooling tunnel. Coolers are attaching the nylon backing which allows the assembly of transistors without washers, and thus better transfer tepla.DPS amplifier is at the top of the tunnel and the transistors are soldered from the bottom of PCB.
Output: 680W/2R, 450W/4R, 260W/8R
Minimum speaker impedance: 2R
Bandwidth: 10-180 000Hz/-3dB
Maximum permissible voltage: max + /-80V
Fusing end amplifier: 2x 15A / F
Late connection: approx 1.5 sec
Input sensitivity for maximum excitation: 1.1 V
Slew rate: 35V/us