Multimedia desktop audio, PC Power Amplifier
Keywords: computer multimedia desktop audio production
The audio system provided by the general commercially available computer is often a low-cost multimedia active sound, sound quality, and poor hearing.
The author introduces a homemade audio circuit, using the power amplifier integrated circuit LM1875T that is specifically transmitted by the US National Semiconductor Manufacturing Company (NSC) in the 1990s, and its main parameters are as follows:
TO-220 single column 5 foot plastic package, operating voltage range: + 8V ~ ± 30V. No output power: PO>25W, static current: 50mA, maximum current: 4A, input sensitivity: 630mV, open gain: 90dB, rated gain: 26dB, distortion: 1kHz20WB, THD = 0.015%, conversion rate: 18V / μs, with overload, overcurrent, over temperature and inductive load reverse potential protection.
The power is set to have a small size, the external circuit is simple, the output power is large, the distortion is small, but not only the sound quality is very good, but also the emoticon of the electronic pipe. Itself has a relatively complete protection function, the circuit is shown (a channel, the power is shared).
The circuit is very simple, first introduced from the computer audio line output socket line-out into the signal to reject the amplifier, the 2x100KΩ volume potentiometer minimizes the consistent product, and the impedance is considering the computer sound card audio output capacity. The value is small, the input impedance is large, and the low frequency end response will be better. The signal is input to the 1 foot of the power amplifier through the coupling capacitor. Integrated blocks and simple peripheral circuits constitute an amplified circuit. Changing the resistance of the transconductance resistor RD can change the large amount of this machine, the higher the resistance, the higher the gain, to achieve the appropriate local sensitivity and amplification factor, and its resistance is often selected between 22kΩ ~ 47kΩ. The power plaque output is added to the RC network to prevent low frequency self-exchancing, protect speakers and amplifier circuits.
Selection of components
The coupling capacitor selects a 3.3μF ~ 4.7uF with a blue metal film of 63V without inceptable polypropylene capacitance, and the sound is clearly listened, high frequency is elegant, and the sound is good. After experiment, any electrolytic capacitor has no sound quality than the CBB capacitance.
The power transformer selects power. 1882.70W R-type or ring type, which can also use a good quality EI type. The secondary voltage is AC 2 × 18V ~ AC 2 × 22V, and the rectifier filtered is about DC ± 25V. The rectifier bridge current should be above 10A. The main filter capacitor is 2 × 4700 μF, and the Japanese ELNA high-speed audio dedicated electrolytic capacitance should be used. 100μF electrolytic capacitance and 0.1μF CBB capacitance in the circuit diagram, which are medium, high-frequency signal decoupling filter capacitors, should be used to enhance the amplifier, high frequency sound performance.
When this amplifier circuit has a swift, when the firem is in the homoa, the 47uf feedback capacitor will be shorted, so that it becomes a lagtock. It is said that the frequency is better, and the low frequency extension is lower. But the author believes that the high-power showing, the mid-point offset voltage drift will affect the line output, or the standard circuit recommended by the manufacturer. In order to improve the sound quality, this feedback capacitor does not have to be general ordinary products, but use dark red Japanese ELNA-BP gold-character audio special non-polar electrolysis, hearing is round, mellow, and does not make the integrated block 4 foot DC potential Drift phenomenon.
Circuit installation commissioning
The 3 foot negative power terminal of the LM1875 is connected to the chip heat dissipation end, so when the external heat sink is applied, the shamousing mother must be insulated from the outside, and the outer heat sink area must be large enough, which is advantageous for the heat dissipation of the chip. It is advisable to do with hands. This amplifier can be used with a finished circuit board, and the panel can be self-made since the components can also be self-made.
The debugging of the amplifier is relatively simple. First, make sure the circuit board element is installed correctly, the measurement is correct, do not pass the box, measure the number of power block outputs with the number of power blocks and zero points, if the voltage is within 30 mV For normal, it is observed that there is no change in half an hour to connect to the speaker audition, otherwise, the fault should be excluded.
This circuit as long as the components are correct, the supply voltage is positive and negative (the voltage is slightly small), which is generally installed once.
Speaker unit and speaker
To make sound quality, you have a big relationship with the speaker, you should use the above-level product, such as the full-range speaker unit of Elegant, Taiwan Logitech, Japan JVC. Conditions can also choose a small high-quality finished speaker with a slightly high sensitivity.
Our other product:
