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From the Ohms law formulas...

Posted by EdAInWestOC (A) on July 10, 2017 at 06:21:57

In Reply to: Need help calculating power output for headphone circuit... posted by soulbrass on June 7, 2017 at 07:20:49:

It looks like you will be getting the following for headphone output...

Based on the rated output of 12 watts into 6 ohms, that calculates to 8.5 volts over the 6 ohms load:

Power = (V*V)/R or (8.5*8.5)/6 = 72/6 = 12 watts

For the same voltage output into 502 ohms (or the 470ohm resistor plus a 32 ohm headphone load) you get 143.5 milliwatts.

For a 300 ohm headphone (that would be 470 + 300 = 770 ohm load) you get 0.0935 millwatts.

Assuming my calculations are correct, you are not going to get much output for headphones. IMO, the 470 ohm resistor should be changed to a lower value to be able to drive a good set of headphones.

To be practical, the 470 ohm resistor should be no higher than 47 ohms. With that value you would get 0.911 milliwatts for 32 ohm headphones and 207 milliwatts to drive a 300 ohm headphone. Those are much more realistic power output values for decent headphone listening.

If you are going to go with a nice set of planar magnetic headphones you will likely need even more power. Doubling the output power from the headphone jack can be done by halving the proposed internal resistor from 47 ohms to 28.5 ohms (or something close to that value).

Ed
Life is analog...digital is just samples thereof

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