amplifier help please

[Arlen moulton]

A few weeks ago i made a simple class a amplifier and it worked brilliantly and sounded excellent, a few days ago I built another one using a transistor of the same number and a potentiometer of the same resistance pluged it into my phone and like before it worked really well so then I took it out to the garage and pluged it into my CD player and a small round brown hole appeared in the Transistor any ideas why?

[T3sl4co1l]

Probably the CD player wasn't AC coupled.  Try a coupling capacitor to the base, 10uF or more should do.

[kg4arn]

 Your circuit is also at risk for thermal runaway.  You may want to add an emitter resistor, Re, bypassed by another 10 uF capacitor.  The resistor will provide negative feedback to the bias current as the tendency of the BJT to heat up causes the bias current to increase under a fixed bias voltage.
You sometimes get away without some kind of negative feedback on the bias, if the current is low enough, but there is no guarantee that another transistor will behave the same.
Also, if you are adjusting volume with the potentiometer, you are doing this by adjusting the bias current and the subsequent change in the transistor’s transconductance.  You may want to set some limits by having fixed resistors on either side of the potentiometer.
 
Some rules of thumb are:
Pick the bias current you desire, Ib
Pick Re such that 1V across it will give you that bias current

Pick R2 about 10x Re at the most
Pick R1 about 10x R2
Pick R1 such that R2/(R1+R2) gives you about 1.7V at the base of the transistor.
You can usually eyeball this and get it right.

Or more precisely solve the simultaneous condition:
Pick R2 such that R2/(R1+R2) gives you about 1.7V at the base of the transistor
Pick R1 Such that R1 || R2 is about 10x Re at the most

I attached an example.  This is by no means the only way or the best way to build a class A amplifier, but it preserves your original architecture.
 

[mikerj]

The other issue is the relatively high level of DC being applied to the driver.  Not only will this cause undesirable heating, it will also bias the cone in one direction which at best will reduce the linearity of the driver.