I can't believe no one else has replied! Well, here goes my limited experience with planars:
I received my Hifiman HE-400i planars 1/12/18 and proceeded to break them in (The Owner's Guide suggest they need >150 hr!). The improvement was great - they went from lifeless to the best headphones I've heard. My stereo consist of an Onkyo C-7030 CDP driving my Emotiva A-100 BasX (10/16) 50 Wpc amplifier while it drives my Klipsch R15M's. The Emo amp's line out is connected to it's line in, so I connected the line out to an input on my Musical Paradise MP-301 MK3 6.5 Wpc SE VT Class A amplifier (8/17), which drives my '77 vintage Klipsch Heresys. Both amplifiers have headphone jacks, the SS Emo having 220 Ohm 5W resistors in series with the speaker channels and each 'phone channel - pretty standard - except for the internal jumpers, which can place full power on the headphone jack - not for me! The MP-301 MK3 can be configured to better match insensitive 32 Ohm 'phones - mine isn't so configured.
Both amplifiers sounded good driving my old headphones, Koss Pro-4aa (~1971!) & Sony MDR V6, 260 Ohms and 70 Ohms respectively. I have the remnants of my expensive STAX SR-30 'Earspeakers', thoroughly trashed by a cat. If memory serves me correctly, their speaker-level power supply required ~10wpc- but they had the clearest mids and hi's imaginable, along with deficient bass. The killer was the cheesiest plastic headband - assured to fail (Mine was practically covered in Epoxy patches!). THOSE WERE EXPENSIVE JUNK! How do the stock amplifiers fare with the HE-400i planars? In a word - sufficient! The SS Emo amp runs max normal listening level @ 1 o'clock on it's volume control, while the MP VT amp's volume control is at 9 o'clock. Both amps have high s/n - the Emo >110 dB; the MP > 88 dB - and there was no discernible hum or noise at max volume. The dynamic range of the VT amp seemed wider than the SS amp, making it my favorite. It just sounds more spacious - but not excessively. I used to repair amps - and know one just 'borrows' VTs - the 6L6G/6P3P outputs have a pair of PRC-made EL-34's to replace them with, while I already changed the preamp tubes to RCA 6SJ7's - NOS black metal tubes - made in the USA, they and the Heresys are it for that origin!
In all seriousness, had I not bought the VT amp, I would likely be content with the Emo SS amp - they are that close. I'll have a pair of Monoprice M560's to compare next week - they are heavily constructed. I'll report on them should they be more difficult to drive. Sorry for the slow reply!
John
