Wiring And Schematic

A simple stereo audio amplifier is built around two 7905 negative-voltage regulators (IC1 and IC2) and a few discrete components. The circuit will also work with other 79XX regulators if appropriate power supply is used. Regulator IC 7905 works as an amplifier for the voltages applied to common pin2 (Ground or GND). Also check the LM317 audio amplifier, another interesting circuit.

The minimal voltage drop over the standard 7905 is around 2V and it depends on the output current. Feedback resistors in the IC set the gain of the channel internally. The amplifier is a class-A audio amplifier. The minimal applicable value of R3 for the regulator 7905 is 8.2 to 10 ohms per 5W.

If the required output current for LS1 is below 100 mA, the value of resistor R3 can be 33 to 51 ohms per watt. The circuit works with any load resistance (R3 in parallel with LS1 as the load) under the condition that the regulator is not overloaded with current and power dissipation. However, it is preferable to use a loudspeaker with a high resistance (8 ohms, 16 ohms or more). The amplifier works well with low-impedance headphones having a resistance of 24 to 32 ohms. The voltage difference between the ground pin of 7905 and the output pin is fixed internally.

S2 is the on/off switch. Switch S1 is for mono/stereo selection. When switch S1 is closed, the amplifier works as a two-way mono amplifier. If S1 is open, the amplifier works as a stereo amplifier. If no input signal is applied, the DC voltage on the output of the regulator 7905 should be around –5V, which depends to some extent on the value of VR1. The maximum output current of 7905 can be up to 1A and the maximum power dissipation is up to 15W. Mount the regulator IC 7905 on a heat-sink with thermal resistance below 15°C/W.

 

                                               700W version could criticize a couple of things:

1st very high gain output stage resulting in deterioration of signal noise distance. Therefore 700W version even more noisy.

2nd The absence of multipliers Ube bias current control and maintain temperature stability diagram. The 700W version of the thermal stabilization solved by a single transistor, which can sometimes cause a great loss due to power control is fast enough and has some delays. Therefore JPA400 added to this multiplier.

3rd Protection Error on board speakers, the amplifier is less comfortable and it is necessary to add this protection to the side somewhere special plate.

4th no possibility to correct the offset voltage of the amplifier output, this has a rather large weight in the differential pair of transistors and voltage level. Here this is solved by means of trimmer connected to the input Mark

5th The work points the individual stages are laid pretty low, it will also cause an increase in total harmonic distortion as well as intermodulačního distortion.



All this is in JAP400 removed. The input amplifier is Mark with adjustable offset voltage. Mark is mainly due Preamplified signal for generating the actual end-impedance amplifiers and separates. The differential amplifier is a classic symmetrical with the current 5 mA per couple, which is about 2.5 mA each transistor. Equally, shifted the operating point voltage amplifier to approximately 13 mA. This modified driver will provide enough power for generating terminal transistor and is hard enough. At the end of this time is five pairs of end-type transistor 2SC5200 / 2SA1943. Current policy is converted into the number of transistors. It has a negative slope and replicates the characteristics of SOAR terminal transistors. Current protection for amplitude limitation limits the end-around transistors 7A. As has been mentioned on the thermal stabilization of the multiplier is used Ube, is formed by two NPN and PNP transistors.



The board also includes an amplifier circuit for the fan control. This circuit ensures that the fan speed control depending on temperature. At the temperature to 65 ° C, fan runs for about 30%, it greatly reduces noise. After exceeding this temperature, the fans start running at 100% and lights to signal overtemperature. fans again at reduced power switch at about 42 ° C. Thermal protection is associated with protection of the speakers at cooler temperatures exceeding 80 ° C, the speaker is disconnected. On board is a relay switch that allows stereo / bridge mode, the indikovám LED on the front panel. The amplifier also includes an auxiliary power source to the main board, formed by transistor stabilizer. Due to higher electric circuit protection circuit and fan control. There is also an indicator of an excited, solved by the presence of the indicator signal and clip detector.

Technical parameters:

Output power:                      2x 400W/4R, 2x230W/8R
Minimum holiday zázěž:         4R
Slew rate:                             45V/us
Bandwidth:                           8-150 000 Hz /-3dB
Maximum permissible voltage: +-75V
Filter Capacity:                    2 x 20G / 80V
Sensitivity DC protection:    + /-2V
Late connection:                  2 seconds
Fusing end amplifier:            4 8 A / F
Input sensitivity for maximum excitation: 1V

    Outputs from each channel are fed to the two inputs of ICl connected as a differential amplifier. IC2 and 3 are driven by the output of ICl. Output of ICl is connected to the noninverting inputs of IC2 and 3. If the output of ICl approaches the supply rail, the outputs of ICs 2 and 3 will also go high, illuminating LED3. This would happen if the right channel were dominating. If the left channel was dominant, the outputs of ICs 2 and 3 would be low, illuminating LED1. If the two channels are equal in amplitude, the outputs of ICs 2 and 3 would be high and low respectively, lighting up LED2.