250W Hybrid Amplifier

250W amplifier has been tested in the field for a long time, high quality and high power. You can use it with 2 8 ohm speakers or one 4 ohm speaker in parallel. It has low harmonic distortion and high sound quality.

Gain Adjustment and Technical Details

Gain: This is the sensitivity to the input signal. This is adjusted using a voltage divider consisting of two resistors. In addition, a sample is taken from the output and input signals. A 33K resistor is used in series with a 1K resistor from the output of the amplifier to the non-inverting input of the TL071.

Dividing the 33K resistor by the 1K resistor provides the gain. If you find that the sound level is too low without using the preamp, you can increase the 33K resistor up to 100K. If you are using a preamp, you do not need to change the 33K resistor.

Note: The sound output of devices such as phones, computers, etc. is high enough that most do not need to use a preamp.

250W Amplifier Circuit Diagram

There is a transistor protection circuit in the 250W Amplifier design to protect the amplifier in case of speaker failures. 2N5551, 2N5401 stops the power transistors in case of excessive current draw. Normally, when the speaker fails, there is no sudden short circuit, even if there is, the wire burns out and becomes open circuit in a short time. The protection circuit is sufficient in this state. The protection system is not very fast, do not test the output by short circuiting.

You need to adjust the quiescent current, bias setting according to the voltage information given in the diagram. When making the adjustment, short-circuit the audio input and do not connect speakers to the amplifier output

Output Transistors

The output transistors are Sanken 2SC3858 2SA1494 (MT200 Case), instead of these I used classic 2SC5200 2SA1943 transistors (alternative: MJL21194, MJL21193) because the Sanken transistors are large in size, hard to find originals and expensive. Also the PCB size was small. I don’t think there will be any problems with 2SC5200 and 2SA1943 transistors with a good heatsink.

The amplifier transformer can be at a maximum of 2x46vac voltage and a minimum of 300W power. In the high power test of the amplifier, 2 8 ohm 12 inch 300 watt speakers were used in parallel. For full power use, a 4-Ohm RMS 400W…500W speaker is recommended.

 

250W Amplifier Connection Plan

Fake Opamp

In the “200W 500W Amplifier Strong Bass Clean Sound” project that I shared before, I said that the circuit did not work with the TL071 opamp and I used LM741 instead. The same problem occurred in this project, this is the second order, the same problem again, and I realized that the opamp was fake. Be careful not only with the TL071 but also with the integrated circuits that have the same logo.

Source: construyasuvideorockola.com