Download Step 2: Electronic Design power Amp The design of the power amp is really straight forward, and follows the datasheet example in the absolutely excellent application note AN from Texas Instruments, which should be your bible if you want to use the LM For a bridge design the trick is to get the resistor values so that both circuits have the same gain. Using mostly standard resistors some metal film resistors and measuring the exact resistance I was able to find combinations that worked. I introduced a gain switch SW1 to be able to increase the gain. It reduces the R1 value to get four times higher gain.
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You can also check out this video to see a quick overview of the design process. Sound quality is severely compromised when the SPiKe circuitry is enabled, so to prevent this we need a heat sink with a thermal resistance low enough to dissipate the maximum power dissipated by the LM Setting it too low might make your amplifier too quiet. I decided on a gain of around 27 db If these resistors vary much between the two channels, the gains will be different and one channel will be louder than the other.
Metal film resistors with a tolerance of 0. Balancing the Input Bias Current After setting the gain, the next step is to balance the input bias currents by choosing values for Rin and Rb: If the currents at the non-inverting input pin 9 and the inverting input pin 10 are different, a voltage will develop between them. Lower than 2 to 4 Hz is ideal. I started with 1. With an Fc of 1. Electrolytics, ceramics, and tantalum capacitors should be avoided.
A good quality polypropylene metal film, or even better a polypropylene metal film in oil capacitor will sound best here.
At high frequencies, the impedance of Csn is very low, so high frequency current is shorted to ground. The datasheet gives a value of 2.
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