VERY simple heaphone amplifier

[sparkle]

Hi!
This thread is for people that still don't have a nice little headphone amplifier and don't want to spend a lot of money to get one.
Amplifier below is VERY cheap and it works nice for me. I use it with my MBQuart QP450 Professional as a portable amplifier when I work on my computer or somewhere I don't need Hi End but good sound. They are 300 Ohms. My friend use this amplifier with his Grado SR80 with even better sound.
The circuit is very simple (the idea comes from my friend – he use the same topology only a little bit bigger to drive his loudspeakers- thanks Darko).
He gets all the credits.
Regards
daniel

[sparkle]

some pictures:

The output cap's are Roe 2200uF/40V - nothing special. Cap's in power supply are 4700uF Matshushita- all of them. I have a little hum from the power supply so one should consider a better power supply

[sparkle]

some more:

[sparkle]

Potentiometer is blue burns and the wires are silver with teflon insulation......
regards
daniel


p.s. it is not an high end but it works very nice - so nice that no one could complain about it- it has everything what a nice little amp should have in a sound and it is CHEAP

[tschrama]

Hi Sparkle,


250mA bias and 47K//47K resistor ... shouldn't that be 47R//47R?

greetz,
Thijs

[millwood]

one small suggestion to you: split the collector resistor into, and connect the pot to the junctionof the two resistors. This way, there is certain level of feedback to maintain very stable bias for the transistor.

the schematic is posted under "simple preamp". except that I used just one mosfet but you can try various medium power bjts with no ill effect.

[azira]

Nice simple CE amp...

1uF input capacitance seems kind of low. Using 2.5k impedance to gnd you would have a cutoff around 60Hz... I think you might want to raise that to 5uF or 10uF.

Do you hook up the headphone reversed polarity like on the zen amps?

[destroyer X]

Good looking machine..... wood made it full of "class"
very good!

Carlos

[sparkle]

OOOPPS!
Resistors are two 47R/5W in paralel
Millwood - thanks....
Azira- I have thought to add little more of the input cap. Thanks for the suggestion.


I have forgotten to say - my recitifier diodes are MR824 form motorola and input cap is wima 1uF (will change that to something bigger.
regards
daniel

[lineup]

nice little project, sparkle!
Very!

for headphones amplifiers are many ways to go
from
- very advanced Op-amp based
- extremely complicated discrete amplifiers
to
- simple 1 OP-amp circuit
- a few transistors
- one single power transistor follower ( buffer )

I like this project.
You have built any other amplifiers?
Or new version of this one?

PICTURE of Circuit in box:


regards
lineup