EveryCircuit - Hi fi amp

10 years ago

Nice, but the bootstrap 100uF cap suppose to connected to the output and not behind the 22kOhm. Keep it up!

10 years ago

It was spose to be it auto connected and i forgot to move it, all sorted now, altho i will say on a real version you would also need a miller compensation cap between the collector and base for stability. Its not really need in simulation tho.

hurz

10 years ago

On more thing, this 500mOhm temperatur compensating resistors seems to me the wrong side of the power BJTs. The job is to make some negative feedback in case of heating up, but this is only working on the emitter side. At least the driver BJTs have to be mounted on the same heat sink.

mikey5869

10 years ago

No its not a darlington pair on the o/p stage it has nearly 100% feedback thro the emitter/base connections in the o/p transistors. No the drivers should not be thermally conected to the o/p pair as that would over compensate and lead to instability. http://www.electronicecircuits.com/wp-content/uploads/2011/07/Class-AB-Transistor-Audio-Power-Amplifier-Circuit-Diagram.jpg

hurz

10 years ago

Will check this website. Probably the 500m are just short circuit protections

mikey5869

10 years ago

The 500mohm are there to limit the biasing current thro the o/p as this simply circuit only uses diodes for biasing and has no adjustment, the value can be lowered if you can deal with the extra current/heat thro to o/p pair. However they cannot be removed completly as the o/p stage would draw silly amounts of current.

hurz

10 years ago

I was thinking a little about that, i dont think it would overcompensate, it would even lower the compensation. This resistor is doing its feedback to the push pull driver transistors and has to be as cool/stable in temperatur as possible because they see the voltage drop and lower the driver current for the power stage. BTW, the link is just a picture and not the original project, anyway i found it but it look different you what you put here as circuit. Keep it up

mikey5869

10 years ago

Trust me ive built it and so have hundreds of other people. One of the great things about electronics is the fact that many things that dont work in theory work perfectly in real life. Try this link instead mate . . . http://sound.westhost.com/project03.htm

mikey5869

10 years ago

Plus the o/p resistors do not provide the feedback, they are only there to limit the class a/b biasing current, if you swap the final o/p transistors for mosfets and change a couple of resistor values in the same circuit it is poss to remove the o/p resistors completely. They have nothing to do with thermal or signal feedback, they purly limit the biasing current thro the o/p pair.

mikey5869

10 years ago

Without being rude may i ask what qualifications and experience you have with electronics, audio in particular?

hurz

10 years ago

Dont worry, i just like what your are doing here. Keep it up please

thebugger

10 years ago

Aren't these resistors there to compensate for temperature and hfe drift to keep the transistors from overheating. What hurz is referring to is ballast resistors i think. As far as i know they are placed at the emitters when multiple transistors are used to distribute the current evenly through them even though their hFe is slightly different.