Headphones amplifier

266

03:34:07

Simple and high fidelity sound 

published 10 years ago

hurz

10 years ago

Nice simple reliable one. Keep it up!

thebugger

10 years ago

Your biasing is a little low. The output transistors are barely on. This is true class B amplifier. Since headphones are a higher impedance load (often being 32ohm,64ohm and up) they will not drain the battery easy, even in class A mode. I suggest you biased it slightly more to enter class Ab mode at an expense of a few percent efficiency. Seeing as how i keep my headphones on a low volume, a class B mode will introduce very much distortion at such levels.

hurz

10 years ago

It does already having 4 mA quitesense current which make such a lowpower headphone amp clearly a class AB.

eeveleigh

10 years ago

If it was class B there would be horrible crossover distortion and there is not.

hurz

10 years ago

I also don't see any crossover distortion. 4mA idle current is much enough. And total power dissipation with about 160mW is also ok and need no class A waste of power, specially as mobile apmifier.

thebugger

10 years ago

Even in class B mode the output transistors must be slightly biased due to the imperfections in their characteristics. 4mA is juat perfect for class B. For class AB I'd say 20-30mA quiescent current would suffice.

thebugger

10 years ago

I'd make this circuit slightly different. I'd use bootstrap instead of the current source, I'd add an emitter resistor of some value to increase the linearity slightly. I'd add frequency dependent negative feedbacks here and there and I'd certainly make the bias point variable and not fixed like with the diodes. Anyway this is a working circuit and i congratulate you for that.

hurz

10 years ago

Anyway, you can do what ever you want, but 4mA does not show any significant crossover distortion even with input swing of 1mV which is 60dB below 1V. I dont see were you got this magical 20 to 30mA, which would just waste power while standby and dont improve the quality while listening. Over engineering effect?

thebugger

10 years ago

20-30mA is hardly wastefull. I usually like to place my amps deeper into the class A region (100-200mA) but since this is a portable version it's gonna have to preserve battery.

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