So my new integrated amplifier states in the manual that only headphones with a minimum of 50 ohms should plugged into the headphone jack. So I take it this means that there is not a lot of current available through the amp powering the headphones? But an acceptable power supply?
Thanks, glad that I could help some. It's not really too hard to understand once you realize that you have to think in terms of voltage/current & power into the load.
what the int. amp manuf. is telling you is that do not apply a heavy (current) load than a 50 Ohms headphone or else the headphone will ask for too much current that will stress the internal headamp. Nothing's going to happen if you drive a less-than-50 Ohms headphone occasionally but over time, the electronics in the headamp will fatigue. You can go higher in the headphone impedance - 100 Ohms, 120 Ohms, 220 Ohms & keep checking how the headphones sound. As the headphone impedance increases, the current pulled from the int. amp headamp will go down & down but the voltage swing will go up & up. At some headphone impedance, your ears will let you know that it's not longer sounding dynamic enough. Once you find that, you've found the upper limit of your headphone impedance.
The one thing that I find confusing though is that most home amplifiers that can handle lots of current are usually expensive. My guess would be because of dealing with the heat generated.
yes, this is one reason - larger heatsinks get very expensive. There are many other reasons: the transformers get very heavy & physically very large in diameter to accomodate very large amounts of current. Thus, they become very expensive. To accomodate a larger xformer, the chassis becomes bigger. More machined metal, more expense. To handle large current, you need higher amperage recitifier diodes - these are also expensive. Then, you have to heatsink these rectifier diodes really well otherwise their performance derates very rapidly. Again, internal heatsinking takes space & money. This is passed onto the customer.
It's a snowball effect when you make a high current amp.... ;-)
But in terms of headphones, an iPhone can easily muster enough current to power a lower impedance headphone such as 16 or 32 ohms. Is it because the amount of current is so small at that point thats not really a big deal? But voltage is because its battery powered?
That's right. The diaphragm of the ear-bud headphone takes that kind of current that can be supported by a micro-electronics circuit inside the iPhone. As you correctly stated, the voltage peak-peak swing is limited by the battery which can be 4.5V when fully charged & then decays to 3.5V when discharged & everything stops working. The electronics inside an iPhone or iPod Classic is just about good enough to drive the Apple-provided ear-buds but try to drive, say, an integrated amp line-in input (I did that before I got my iPod dock) & it sucked big time! No umph at all & a very flat/flacid playback. If I went a little above 75% of the volume, I'd get distortion thru my speakers (I was clipping that internal headamp) as it was struggling to drive the line-in of my int. amp.
