LED VU METER USING THE LM3915
 
   Simple circuit using the LM3915. It does not differ in a lot of points from other applications with same IC. The circuit is a Vu meter that will be connected in the exit of power amplifier. It can be adapted in it's  sensitivity so as to it works with amplifiers that have different out power, we change the R1 value of according to Table 1. The value that will be found if it does not correspond in standard resistance price, it should selected the next standard value or if you want the biggest precision it should you put resistances in series or parallel so that you achieve the value. You can use various types Leds round or square, so that you take the optical and cosmetic result that you want. With switch S1 selects if the Vu meter works as bar or dot. In the place ON [switch closed] the operation is bar and in place OFF [switch open] the Led operation is Dot. In the Bar mode the power consumption goes up, because all the Led's it can reach up to 150mA. For amplifier with two channels obviously it's that it will be supposed made two same circuits, one for each channel. The voltage circuit supply is +12Volts. The source for  this supply should become from the existing power supply of power amplifier. Usually the power amplifiers work with supply bigger than +12Volts that it needs the circuit. For this reason added one stage of voltage +Vp attenuation in +12Volts. This becomes with the stage that is found in the  line and with the IC2. That is a regulated stabilizer. The use of small heatsink is essential because the voltage differences of input / output are big so that we have increase of high levels of temperature. The use of R5 helps in the fall of voltage so that goes down the voltage in the IC2 input in lower levels. The calculation of this resistance value is simple using the Ohm law. The voltage in the IC2 input should it is bigger than +16Volts. For example if the voltage of power amplifier is for example +50Volts it will be supposed we have voltage fall 50-16=34 Volts above in R5. For current with mean 50mA that it wants circuit [can reach until 150mA] the price of R5= V/I=34V/0.05A=680 ohms 2W. Perhaps it needs boost or decrease this value after tests. Because of the resistor heat  is it placed in some distance from PCB. The regulation process of IC2 with the TR1 is a simple adjustment. If you have benefit possibility of continuous voltage +12V from some point of power amplifier, leave out the R5, the IC2 and the components that are found in the power line.
Parts List