TL;DR, trying to understand if the amp should be able to push the cans to a max 110dB, 115dB or 120dB, or more. Hi all, first, sorry for the long post. I have been looking for a portable headphone amplifier for a HD650 and an upcoming HE4XX. I got a bit intrested in a few sub $250 units, iFi iDSD Nano BL in particular (one of the few with single USB for data and charging). Most of them are rated at around 300mW at 32 ohms. I asked around in many threads, but kept getting the response that most of them barely drives HE4XX. I found this a bit confusing, which could be due to my lack of proper understanding of the topic. Hence this post. I am trying to fill in the holes in my knowledge of the topic, so as to decide on what to get. I keep hearing that modern recordings have a dynamic range which will push the ceiling about 20 dB above average listening levels. Assuming one listens at 90 dB (I don't think I do at that level), that should be 110 dB. So, is it enough to select an amp which will push the headphones to 110 dB. Or, do we need it to be pushed to 115 dB, 120 dB or more? Also, what would be the requirement of old classical/rock music (as in how many dB above normal listening volume)? As I understand, most people feel that there is some distortion in the sound above 3 o'clock position, even in relatively good amps, which approximates to about 70% of the total power of the amp at that load for a log/commercial pot. In amplifiers one obeserves that the actual measured output of an amplifier is sometimes only around 60% to 80% of the company rated power output. I don't know if it is applicable to headphone amplifiers. Still, if I assume that the actual output will be only 70% of the rated output, that gives us about 50% of the total rated power, at 3 o'clock position. As an example, let us take iFi Nano BL and HE4XX (stuff I am considering). iFi rates the amp at 285mW at 30 ohms. HE4XX is rated at 93 dB/mW SPL at 35 ohms, but innerfidelity measurements showed it at 49 ohms, which puts the Nano's power at around 174 mW. If we take a safe 50% of it, it is about 87 mW. Now HE4XX can achieve 112 dB at that power. So, will this power be enough for someone who listens normally at 90dB? How will it change with old classicals vs modern recordings? Also, I keep reading that planars need more current that voltage. But my understanding was that current and voltage are related to load. So, if there is not enough current, the voltage will also be lower. So I am having a hard time understanding how there can be enough volume but the cans sound weak. One reason I could think of was that when the current reaches peak achievable values, the amps characteristics starts to change or audible distortions starts to appear, changing the sound signature. This could be the cause of the weak sound even though the volume is satisfactory. Am I right about this? If so, at what percentage of the peak current can we expect an audio amplifier to start behaving erratically?