I had the 250ohm until the coiled cable had a fault which cut out the right channel and amazon sent me the DT 880 660ohms as a replacement. I found A3 plenty loud enough with those. Anything past 6 on the dial was just too loud. How much louder does the amplifier need to go to drive them well? Not sure who it was, but before i got the 600ohms, I did ask on this forum if the A3 would be ok and someone told me that they didn't have problems with it. In my case, with most music, it is loud enough on high gain and very close to (or at) maximum. With a very limited amount of music, it admittedly does distort and does so far more with bass boost on. About a year ago, I did even buy the A5 as I could do with more volume so I'm not pushing the amp so hard but I was really disappointed with it. Given the specifications saying it was 800mw at 32 ohms vs 270mw for the A3, even for 600ohm headphones, I was really surprised just how small the difference was. With these headphones, it only seemed slightly louder. At double the price of my A3, I was disappointed enough to return it.
I also sometimes like a bit of bass boost and the A5 had the most horrible bass boost I've ever come across. From graphs I've since noticed on this forum, it boosts it by around 6db from right at the bottom of the frequency range to 100hz, but still is at +4db at 200hz and still seems boosted above that and to me it completely ruins the midrange. The A3 peaked by around +6db at 75hz and rolled off very quickly and was close to being flat again by the time it goes up to 100hz
The only device I have that actually gets these headphones very loud is my integrated amplifier. Pioneer A-209R. Turn the dial past 10 o clock and you will seriously struggle to go any further. Why would a cheap device like this have a better output than many really expensive headphone amplifiers specifically designed to drive power hungry headphones? The reason why I don't use it is because I have so many different input devices (introduce a bit of interference) and it is is in an awkward location. Otherwise, if there was such a thing as a headphone amplifier like this, that would be ideal for me. Having bass, and treble for + and - 8db adjustments as well as a loudness and direct button is just nice to have.
Any suggestions for a better headphone amplifier would be appreciated. I would prefer it to be a portable battery powered one as I don't just use them at my desk. I'd looked into the topping NX3 which looked pretty loud from the specs, but also looks like it will have a muddy bass boost similar to the A5 from what some have said. My A3 is manageable, but I do occasionally want more volume as well as the bass boost being usable without distortion.