SHA1 Stereo Headphone Amplifier Kit

tinny sounding like from a poorly recorded CD. R7 and C12 on the output side of the LM386 is for preventing oscillations due to the inductive nature of a speaker coil being driven by the LM386. This makes the load of the speaker look more resistive than inductive, which prevents “motorboating” of the audio signal. C15 is another coupling capacitor. It couples the amplified output audio to the headphones with out allowing the DC level on U1 pin 5 to be applied to the headphones. J3 is the input power jack. It provides two functions. First, it allows an external voltage to be applied to VR1. Second, it provides a switch to connect BAT1 to the circuit when no external plug is inserted into J3. When a plug is inserted it removes BAT1 from the circuit. C2 is a filter capacitor. Its main job is to filter any ripple that is coming in on the external DC. VR1 is a 7800 series regulator. It regulates the input voltage to give a +10 volt DC output. It requires approximately two volts of headroom. That is why the external power has a minimum specification of 12 volts DC. C6 is another filter capacitor. Its primary job is to filter the +10 volt output of the regulator. D1 is used as a switch. It is reversed biased (open switch) during battery operation preventing VR1 from drawing current reducing battery life. It drops approximately 1 volt when an external supply is used (closed switch) dropping the +10 to +9 volts. S2 is the power switch. C10 filters the +9 volts DC. Ramsey Customer Use Only Not For Publication

SHA1  5

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