I'm using a 1999 Headroom Maxed out Home to drive LCD-2 rev 2 phones. Audeze recommends 1 watt but I think that is more than than most people need because Audeze's assumptions are conservatively high. The LCD-2 is amazingly efficient for an Ortho, actually play slightly louder at the same voltage than the HD-600s. They're easy to drive and don't need much power, you want a super clean low distortion amp but it doesn't need a ton of power.
Audeze suggests your music has 60 dB of dynamic range. Sure you can invent sounds that have 60 dB or more of dynamic range but the only music I know of with 60 dB of dynamic range is something like the Carmina Burana or the 1812 Overture with cannons being fired. In this case if you listen with the quiet parts at 90 dB SPL the loud parts will make your ears bleed and possibly explode your head.
After saying that, Audeze provides a more realistic example: listen at 90 dB with 30 dB of dynamic range.
Power in dB is 10*log(ratio), here it's equal to 30 dB, so we have ratio = 1,000.
30 dB louder requires 1,000 times the power so that's 1 milliwatt to 1 Watt.
But listening with the quiet parts at 90 dB SPL is super freaking loud. Most people who listen that loud are listening to rock which has a lot less dynamic range (more like 12 dB instead of 30). So let's get realistic: suppose we listen with the quiet parts at 67 dB SPL and there's 30 dB of dynamic range.
Peaks will be 97 dB SPL.
The LCD-2 needs 1 mW for 90 dB, so for 97 dB it needs: 10 * log(x) = 7 --> x = 5. That's 5 mW of power. Five milliwatts. That's nothing!
Now if you really crank it up, suppose you listen with the quiet parts at 80 dB SPL, so peaks are 110 dB SPL. That's ear bleeding loud, but hey...
That's 20 dB louder than the reference 90 dB @ 1 mW, so we have:
10 * log(x) = 20 --> x = 100
So we need 100x more power, which is 100 milliwatts.
Still nowhere near 1 Watt of power. Any decent solid state headphone amp will put this out nicely, and most tube amps should too.
Of course the amp could run out of current and clip, so how much current would it need?
The LCD-2 has an impedance of about 50 ohms.
Power is current squared * impedance, so 0.1 W = i^2 * 50 --> i = 0.044. That's 44 milliAmps. Any decent solid state headphone amp should be able to do this no problem. Even most tube amps should.
Anyone feel free to check my math, but I can say the LCD-2 sounds absolutely freaking great with my Headroom Maxed out Home. It's a beefy little amp with super smooth yet detailed sound, ruler flat response with negligable distortion, perfect for high quality recordings of acoustic music. Those OPA627s are mighty smooth and clean and the little toroidal power supply shows nary a ripple on the DC. I'm not sure where it maxes out in power, but I've bench tested it to about 250 mW and 180 mA of current, at which it has no sign of clipping, all harmonics in spectrum at -85 dB or lower. That's way louder than I will ever need.
I'm glad this post exists on here, because for so long I've seen people say things like "that amp running a max of 1 watt is only the bare minimum for your LCD 2s" yet every now and then I would see a post of someone using them with an amp that maxes out less than 1 watt and they love the sound, even compared to more powerful amps. Even on the Audeze forum post that has these power suggestions, theres a guy running them with an amp that outputs about 500 mW into 50 ohms and he loves the sound. So thank you for showing all the proper math behind why this is true. I thought of the analogy of like driving on the highway: one car with 200 horsepower is driving at 65 mph, and then next to it is a supercar with 700 horsepower also driving at 65 mph. if 65 mph is the same as maximum normal listening volume, then you see how whether you have 200 horsepower of 700 horsepower, you still easily achieve the same level of volume and dynamics. granted the lesser powered car will be using a bit more effort to maintain 65 mph, whilst the higher power car will be borderline idling in first or second gear. But in musical and amps terms, you would never really notice the difference. What you would notice is how good the ride is, and as long as your car can at least make it to 120 mph, then how good the ride is, is the only real difference and important factor.
Also I'd like to note that I play drums, and for anyone else here whose ever played or stood next to someone who was playing, without ear protection, you will know exactly what 105-120dB actually sounds like. Because I feel a lot of people on here might not have a clear picture of how painfully loud that really is. Its a volume level that after 20 minutes of sound, you will literally be partially deaf for a good hour or two after. A loud cymbal will physically make your ear hurt as you feel the sound waves vibrating the inside of your ear (high pitched frequencies I should add). So yea, if you think you listen to music on the loud side and need an amp that can go close to 110 dB (excluding dynamic peaks) then you might want to rethink the dB number that you're actually listening to lol.
On another quick side note/question, I tried plugging in my LCD 2's into my laptops 3.5mm jack just for curiosities sake (since that jack can drive my Denon d5000 pretty well) and in turn it sounded horrible, I mean not in qudio quality, but like it literally was too quiet to actually listen to it to any normal level at maxed out volume. I should mention to get the Denon's even at normal listening volume I have to max it out lol. So I was wondering if it only takes 1mW to get 90dB out of the LCD 2, and like 116dB for the Denons (I think, close to ti at least), then how ridiculously low of an output power does my laptop's 3.5mm jack have lol? According to the math it has to be less than 1mW lol, which is super low.