Trouble Getting SE Circuit to Work


2009-05-07 3:08 am
I can't get this circuit to work even though I think it should. I can get just a tiny bit of output from the circuit if I turn the source up to max but the source is louder hooked directly up to the speaker. I can get the offset voltage to zero and the circuit seems to idle okay (around 50mA) as both the FET and the resistors become warm so I'm not sure what is the problem?



Paid Member
2007-09-15 8:14 am
The 240 ohm resistors are limiting the current that can be delivered to the load. Work it out... 24 volts across 480 ohms (the upper chain) can only deliver 50 milliamps.

To get usable power into a speaker means those resistors would need to be much much lower but beware, this type of amplifier (Class A) would then need a large power supply and it would generate lots of heat.

Your speaker coupling cap also needs to be much bigger (at least 470uf for you to play around with this) but again beware, an electrolytic can be reverse biased in this circuit and that means it could go pop :eek: