Basic knowledge of electronic components - application points of integrated power amplifier

About the selection of output power, enthusiasts can use the power of two times to determine, do not blindly pursue high power. Excessive power, not only the cost rise (transformer, radiator, filter capacitor, and even the chassis have to increase), and heat design, anti-jamming, layout and so on have become difficult. It costs more, but it makes unnecessary waste.
In addition, the integrated amplifier comes with two types of heat sink insulation and non insulation. Insulation class, such as LM series suffix TF varieties, using an integral plastic sealing process, only the integrated block and radiator can be directly fixed. Most of the metal exposed heat sink integrated amplifier is non insulated, the heat sink and the negative supply is used in the power amplifier and do not contact with other parts (especially the casing and the ground), otherwise will damage the integrated block. Through comparison, it is found that the output power of non insulated power amplifier block is slightly larger because of lower thermal resistance.
On the choice of the form of circuit, the author thought that the circuit is recommended by the manufacturer to voltage feedback are given out and the test index is also based on this, since the circuit should be recommended, can better play the performance of integrated block, in fact. Current feedback and DC servo are useful attempts for integrated power amplifier applications, but the results should not be overstated. The author has produced two kinds of feedback power amplifier by LM1875, and there is not much difference in subjective listening sense. DC is necessary, and for low offset voltage varieties (such as LM1875), the direct input to the ground capacitor can be directly eliminated. The DC servo circuit complicates the circuit, and the author thinks it is not necessary to adopt it.
The DC voltage should not be too high, otherwise, not only the heating of the integrated block is serious, but also the sound quality is deteriorated, and the misoperation of the overvoltage protection circuit may also occur. Priority shall be given to the manufacturer's recommended voltage. If not, the DC voltage can be obtained by using the limit voltage * 85%, and then the AC voltage is divided by the DC voltage divided by 1.25.
Power amplifier does not need to use regulated power supply, but the power capacity of the power supply must be enough. The power of the transformer is two times the total output power and is shielded. The rectifier tube should be of low internal resistance and a small capacitor at each end of each tube. The capacity of filter capacitor should not blindly, not overdo sth., per 10W2200 F calculation. If the funds are sufficient, the effect is more obvious on the transformer.
There are not many peripheral components used in integrated power amplifier, and high quality products should be selected. The coupling capacitance is better than the MKP, so it is not suitable to use electrolysis. The larger capacity bypass capacitor can be tantalum electrolytic, and the small capacitor uses CBB or MKP. Resistance as much as possible using five metal film, the power can not be less than 1 / 4W, conditional use of 1 / 2W. Check components before installation, pay attention to errors and matching. Do not blindly pursue imported supplements, tonic components cost-effective, moreover, many fakes. The layout of power amplifier line should follow 3 principles: 1., one point grounding. The input, output and ground of the integrated circuit shall be individually connected to the "point" of the filter capacitor, and shall not be lapped so as not to introduce noise. 2. size signal separation. The input signal should be far away from the output signal and power supply, the specific design board, there are two ways, one is the single flow direction signal method, the signal from the printing plate at one end of the input, the other end of the output; the other is a ground isolation method, namely the size of signal with ground isolation. 3. transmission mask. The lines that transmit small signals must use shielded wires and the shield is single ended. Other aspects, such as symmetrical layout of components, enlarged ground wire area, increased width of large current copper foil (even tin, etc.), are also beneficial to noise reduction.
Since the output voltage swing of digital audio source is enough to reach the input sensitivity of most integrated power amplifier, the front stage only needs the function of buffer, volume control and tone distribution. Before the class there are two commonly used categories, one is operational amplifier type preamplifier, high index, its better sound quality, but must use high-quality potentiometers; the other is the class composed of special volumetone integrated circuit, such as LM1036, LM4610, TDA1524, low cost, easy to be made, that the ordinary the potentiometer does not affect the sound quality effect is satisfied, can choose according to the actual situation of lovers.