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Funny, as Mad Dogs impedance are low but still need amping? Care to elaborate?
This is how I understand it from what I've read, but I'm not an expert or know precisely what I'm talking about so don't quote me, haha. Anyone
please correct me if I am wrong. Also, note that I'm talking theoretically.
When trying to determine how hard a headphone is to drive, impedance is a factor, but it's not the sole or determining factor. The two specs you want to look for are impedance (expressed in ohms) and sensitivity (usually expressed in dB/mW or sometimes dB/V).
Now, when looking at the specs for the amp (or portable player etc) you will be using, you want to look at its specifications and look at its power output. For example, it might say something like "30mW @50ohms, 15mW @150ohms." This lets you know that if you have 50ohm headphones plugged in (although headphone impedance can vary at different frequencies so this is not entirely accurate), the amp can deliver about 30mW of power.
Ok, so we know how much power our amp has. The next question is, how much power do my headphones need? This is where sensitivity comes in. Take the MadDogs for example. They have a sensitivity of 92dB/mW (that is, with 1mW of power they will play at a volume of 92dB). To hit peaks of say 100-105dB while playing music, this means they'd need something like 6.3-20mW. (I got these numbers by using
this formula.)
So let's say we want to pair the MadDogs with our hypothetical amp from above. The MadDogs have an impedance of 50ohms (in this case, being orthos, their impedance actually stays pretty much flat across the frequency spectrum), and we know that our amp can deliver 30mW @50ohms. The MadDogs only need 6.3-20mW to hit peaks of 100-105dB, so we know that our amp should be able to drive them to these levels (at what amounts of distortion though may be unsure). However, if we wanted extra headroom and the ability to hit peaks of say 110dB, we would need at least 63mW. In other words our amp wouldn't be able to cut it in that case.
tl;dr
It's probably possible to drive the MadDogs from a decently powerful portable device, just not to super loud levels or with highly dynamic music. An amp isn't
necessarily strictly needed, but not at all a bad idea. Your Cmoy should be enough for the MadDogs.
Also, IMO stay away from the FA-003/HM5/etc. My speculation is that it would merely be a side-grade or even a downgrade.