As we all know headphone amps are not cheap to buy. I think this is the main reason that drives the hobbyist to make their own amps. Most people are familiar with the popular C’Moy headphone amp which is cheap to make and it sounds nice.
But there also other designs available, for example this class A MOSFET headphone amp. The author designed and build it because he’s 32 ohm Grado SR80 headphones didnt’t sound good on it’s computer soundcard.
An IRF610 MOSFET was used by the author but there is a wide variety of FET devices that can be used instead. Unlike the C’moy amp this amp was primarily designed to sit on a desk, it’s bigger the MOSFET needs heatsink cooling so this wouldn’t fit the portable category of amps.
A LM317 regulator is used for the constant current source, and the current is limited to about 250mA. In the end the sound is better than on the sound card and it was a small investment as most parts were salvaged.
It’s not too difficult to build something similar but it will sure help to have some experience with similar circuits.
MOSFET Headphone Amplifier: [Link]
The main PCB for the charger is a single sided, 1.6mm tick printed circuit board. The DC/DC converter is now integrated within the charger in order to allow the charge of high number cell packs. The people that charges only few batteries (12Vdc supplies sufficient) can not mount the components for the DC/DC converter saving the money of this part. The DC/DC converter part is a generic step-up converter, capable to deliver 7.5A and an output voltage of 24Vdc, starting from a 12Vdc supply. The main parts are the following:
- PWM controller UC3843 very cheap and easy to find
- Power inductor from Bourns, type 2306RC (27uH, 15A), Farnell 1167731
- The power diode is a schottky type,and a N-type mosfet can be generic: all the two components are in case TO-220
Universal Charger: [Link]
This is a simple do-it-yourself (DIY) headphone amplifier project that is fashioned primarily after the Class A MOSFET Headphone Driver project by Greg Szekeres and to some extent Mark’s DIY Class A 2SK1058 MOSFET Amplifier Project. The amplifier concept is simple and follows a typical single-ended class A circuit utilizing an active constant current source (CCS) in place of a passive resistor. A CCS doubles the efficiency of the circuit over that where a passive load resistor is used, bringing it to a maximum of 25%.
Class A Headphone Amplifier Boost Your Sound: [Link] – [via]
Ignition coils are essentially pulse transformers. Transformers that work using pulses of current, instead of standard alternating current. These pulses that are applied to the primary coil are magnified and the voltage appearing from the secondary coil can be up to about 40kV.
To run the ignition coil outside of a car, specialised circuitry is required that produces pulses of voltage to the primary coil. A very common design (the 555 timer driving a MOSFET) can be used for that.
After putting everything together you can get some nice sparks out of that ignition coil, really cool effect.
Playing with ignition coils: [Link]