HiFI Headphone Amplifier

Posted on Feb 6, 2014

This is an article about my new PCB design for CMoy headphone amplifier. Main feature is that the new PCB fits exactly to the classic Altoids tin-can. This new CMoy incorporates moreover bass-boost circuit and constant current charger for 9V battery. P1 is the volume potentiometer with On/Off switch. C2 is coupling capacitor. R2 defines the input

HiFI Headphone Amplifier
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impedance of opamp. R3 and R4 define the gain of the amplifier (5x in this case). Rb and Cb form bass-boost circuit. These components increase the gain for low frequencies. For the low frequencies the gain is 14. By increasing the Rb resistors you can increase the gain for low frequencies and vice verse. You can decrease the cutting frequency by increasing the Cb capacitors. Bass-boost can be deactivated by shorting out Rb resistors. As a opamp I use OPA2132, but many others can be used as well like OPA2134, OPA2227, NE5532, . C3+ and C3- are blocking capacitors for power supply for opamp. R5 is optional, but to avoid some bouncing at the output the value should be around 22 ohms. V1 is a Rail Splitter which creates virtual ground. C1 is high quality blocking capacitor with low ESR. Resistor R1 limits the current through LED. The value should be modify according the type of LED. D2 limits the maximum voltage in the input to 12V. U2 together with resistor R0 create constant current source for charging the 9V battery. In my case the R0 has value 47 ohms and then the current is around 25mA. Cin is tantalum blocking capacitor for U2. D1 is Schottky diode for avoiding any damage when the voltage with opposite polarity is connected. I designed the PCB with two rounded corners. The PCB fits exactly to the Altoids tin (see pictures below). On the PCB are also nice pictures of input jack and headphones. The resistors and diodes must...

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