Beresford Bushmaster DAC

[Reid Malenfant]

You haven't been keeping up to date with headphone amp design technology . The TI TPA6120 IC has been used in headphone circuits for many years now by companies like Benchmark in their DAC, and by many others in stand alone headphone amps. Other ICs are also available that can be used for headphone output circuits.

As for your point on voltage output: can you expand on this for the benefit of all the readers of AoS? Maybe you can make a simple list of what current and voltage is required from a headmp in order to produce the maximum permitted power output to drive headphones at various impedances?

I'm not really interested in ICs A headphone amplifier is going to supply low enough power to make it worthwhile using a discrete circuit in Class A. I don't see many ICs in tube headphone amps so why incorporate one into a solid state version if you want the best quality?

As for expanding on things, sure!

Beyer Dynamic manufacture a 600 ohm version of the DT990. This has a sensitivity of 96Db/mW & a power handling capacity of 100mW or 0.1W. This means it can reach peak levels of 116Db.

Now if you look as this little screen grab you'll notice the extraordinary sound levels possible with symphonic music...

SPL levels at 3m.jpg

Taken from http://www.soundadvice.info/thewholestory/san12.htm

So lets assume you are sitting 12m away from the orchestra The sound will be approximately 12Db down on those figures as it drops by 6Db when the distance is doubled. That still gives peaks of over 120Db.

Now we aren't going to ask the headphones to do what they can't do so we'll take the peak value of 116Db which they can do...

0.1W x 600 ohms = 60. square root of 60 = 7.7459V RMS neaded to produce this. Peak voltage = 7.7459 x 1.414 = 10.95V PK. So the supply will need to be approximately +/- 15V DC allowing for component losses.

Now type 4 ohm headphone into google, you'll find there are quite a few

As I mentioned previously I'd like a no compromise headphone amp that could drive any headphone to full volume... So lets just assume that these hypothetical 4 ohm headphones have the same 96Db sensitivity & the same maximum power handling. Ok I know it's not likely to be exactly the same but there is no point in sucking eggs...

0.1W x 4 = 0.4. square root of 0.4 = 0.6324V RMS needed to produce peak output. Now comes the interesting bit as I want a class A amp

0.6324V RMS x 1.414 = 0.8943V Pk. current needed in a push pull class A amp is 0.8943 divided by 4 ohms = 0.223A. Divided by two again as it's push pull = 0.1118A.

Now as we want to drive any headphone from 4 to 600 ohm to full volume we need that +/- 15V supply & the 0.1118A current which works out at 3.353W dissipation per channel or a total of just under 7W both channels.

I don't see any IC being happy with that kind of power dissipation myself


Hope that's good enough for you Stan


Now I know you may well come back & say the the EU has restricted the maximum sound level that is allowed to be produced by a set of headphones & thus you have your hands tied, but I'm not interested in what the EU says in all honesty