Hey thanks you guys

"DOUBLE AMPING EXPLAINED"

What you have to consider when amping is what you are doing.

Each "amp" has "gain" and gains multiply.... In fact amps are just gain devices...

So say AMP1 has an output of 2 Volts RMS as many DACs do...

And say AMP2 like say an EF1 has a gain of 3 (I'm just guessing)...

Then your maximum output voltage will be 2 Volts X 3 or 6 Volts RMS. (Assuming AMP2 is capable of an output of 6 Volts RMS)

Now depending on your headphones this may already be way too much like in some 16 Ohm IEMs.

That would be 6VoltsX6Volts/16Ohms or 2.25 Watts!!!

Most headphones can only handle 200mWatts MAX!!!

or .2 Watts!!!

So that would be a BIG ISSUE and you'd smoke those headphones fast at max volume.

IEMs can only handle way less then that, just a few milliWatts, like 20ish...

Example #2

You've got 32 Ohm headphones and have a DAC that puts out 2 Volts RMS.

Well in 99% of the cases... You're already done. (Assuming your DAC can drive 32 Ohm loads, some can't)

No amp needed as most 32 Ohm headphones are very efficient.

Example #3

You've got 300 Ohm headphones.

You've got a DAC or MP3 player putting out about .65 Volts RMS.

So your power into your 300 Ohm headphones is 1.4 milliWatts...

In some cases that is still enough as headphones are very efficient.

But the headphones say are rated for 200 mW of power.

Well to get 200 mW into 300 Ohm headphones you'd need about 8 Volts RMS.

So since you've got .65 Volts RMS coming out of your DAC or MP3 player,

and you need 8 Volts RMS to MAX out your 300 Ohm headphones ( and I mean max out...)

You'd need an amp with a gain of 8/.65 or 12....

Now not too many amps have gains of 12 , that is a lot from my experience...

So you MAY need to double amp that or may not depending on the amplifier.

Specs are almost always given with amplifiers...

And not ONLY would you need an amplifier with a gain of 12 ,

You'd also need to have an amp capable of putting out 8 Volts RMS.

8 Volts RMS translates roughly into 23 Volts Peak to Peak so your not going to get that out of your standard portable headphone amps, or out of most AC powered headphone amps.

But you CAN get high gain, high voltage amps for driving 300 Ohm loads, as that is what they are designed for....

For most applications I find 2 Volts RMS into headphones is PLEANTY of power.

For the other 20% you need about 4 Volts RMS

and for the final 5% you need the 8 Volts RMS.

So you have to consider these factors:

The impedance, efficiency, and maximum power of your headphones ( ie 32 Ohms, 110dB @ 1mW, 200mW max.)

The power, minimum load, and gain of your amplifier. ( ie 200mW, 16 Ohms, Gain of 3 )

The voltage going into your amplifier. ( output of DAC = 2 Volts RMS, output of MP3 player = .65 Volts RMS )