You need something with a voltage gain of roughly 10, so here are two examples of 2xNPN-preamps -- see attached picture ...
http://members.shaw.ca/roma/one.html
:wink:
IanP
Thanks Ian. What class amplifier is this exactly?
I have spotted this one which is similar to the one you have posted except that it employs a class AB amplifier which I have read are supposed to be more efficient.
I would like to play around with this one however I am unable to find a website that shows and explains the calculations.
I have found plenty of pages like this that show the generalised schematic and one good site with a you tube video that shows a specific schematic but the guy does not explain how he calculated all his values.
**broken link removed**
- - - Updated - - -
So this specific class AB amplifier (http://hackaday.com/2011/08/14/build-your-own-class-ab-audio-amplifier/) seems to work sort of...
If I connect up an 8R speaker I can just hear the music from the audio out socket from an ipod if I hold the speaker to my ear.
However the BC327/BC337 pair I am using heats up alarmingly and I can't leave it on for long.
Introducing a series resistor solves the problem - 390R is not enough as the BC's still heat up to much, 1k is either enough or more than necessary.
I am getting DC output, according to my multimeter, of something like 7-8V - that is probably about right for the 555 control pin.
For interest's sake, what would it take to be able to hear the audio clearly on the 8R speaker?
Would I need to power the amplifer with a higher voltage and increase the amplitude of the audio signal?
I would like to recalculate the biasing so that I can run the amplifier from my 12V rail rather than have to add another voltage regulator. But I have not found a website that explains, with examples, the biasing calculations for this type of amplifier.