The PNP's emitter terminal is grounded instead of the collector terminal.

is the formula:Pi= (Vcc)(Vout peak)/(pi*loadResistance) still applicable for this?... the out put has crossover distortion and Im not so convinced that using the default formula for efficiency would give me the right answer for this circuit.I mean you cant use Po= (Vop-p)^2/8RL right? cause the o/p isn't a sinewave anymore?

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    \$\begingroup\$ Q2 is backwards. It would still work but its hfe is rather low. \$\endgroup\$ – Edgar Brown Mar 2 at 0:04
  • \$\begingroup\$ @EdgarBrown I think the hre would be the quantity of interest here, as it's in reverse active mode. \$\endgroup\$ – Hearth Mar 2 at 0:21
  • \$\begingroup\$ @Hearth I should have stuck with beta... But, I don’t think so, technically it should probably be hfc. As it not really a “reverse” h-parameter but a forward one. \$\endgroup\$ – Edgar Brown Mar 2 at 0:30
  • \$\begingroup\$ This is a bad design. It requires the input be at overdrive levels to make the base of Q2 more negative than its emitter, which would cause terrible distortion. You would get better results if Q2 was a resistor or high value inductor. \$\endgroup\$ – Sparky256 Mar 2 at 0:44
  • \$\begingroup\$ @EdgarBrown Well, regardless of what the correct term is, it certainly won't amplify well. \$\endgroup\$ – Hearth Mar 2 at 1:50


Please explain the current paths through Q2. What is your justification for reversing Q2?

  • \$\begingroup\$ well you see its from an experiment manual from our electronics class. The experiment was about class A and B amplifiers... the circuits where messed up (I mean instead of an NPN a PNP BJT was used on the class A arrangement and then there was this guy) and I just wanted to be sure if we can actually use the default formula for output power on this since it isn't a sinewave. \$\endgroup\$ – PHO BOSS Mar 2 at 0:22

Contrary to what some seem to think, yes. It will still be a class-AB stage. Note that it is class-AB, as the diodes ensure some bias current without an input.

Q2 is backwards biased, which means that its collector and emitter are reversed and it will conduct in the reverse direction.

In practice what this means is that instead of a beta of, let’s say 300, it will have a beta of 30 or so. Which in turn means that base current will be much higher than if it was connected properly.

The base-collector junction has a different doping profile than the base-emitter junction. This also means that its forward drop will be lower which, in this configuration, further increases the quiescent bias current.

The large imbalance between base currents of Q1 and Q2 will guarantee that the quiescent bias voltage of the output will be considerably closer to the supply voltage than it would otherwise be.


The class-A circuit with a PNP transistor wrongly used instead of a proper NPN, and this circuit with the PNP transistor upside down might be used in an electric guitar amplifier to produce lots of fuzz distortion.

An audio amplifier output power is rated with a sinewave input. A squarewave input or output produces about double the real output power since it has many added high power harmonics. Peak to peak power is used only by marketing liars.

The two input capacitors are never used in a real amplifier, they are used only in an old school circuit.


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