hey guys - I need to put the "beep" usually made pluggin a buzzer to one of the arduino`s pwm in a pair of earphones-
How to?
I don`t think the ardu will make it sucessfully driving 90 and 800 ohms earphones, so I was thinking about using an amplifier. right?
Are there some commercial cheap things you can suggest to me or I have to make my own (VERY) crappy amp?
Thankyou so much 
You could use an LM386. It's a single chip power amplifier that's good for about 125 milliwatts.
would it be good even with such high impedance earphones?
It should work fine with high impedance earphones. The datasheet shows that with a supply voltage of 5V the output voltage swing is about 3.3Vp-p with a 16-ohm load and about 3.9Vp-p with an infinite load. So with your earphones the output would be somewhere between these points.
and since I need thoe earpone just to BEEP cant i just control them with a fairly small transistor driven by the ardus pwm? It doesnt need to be music, it`s just an alarm