Originally Posted by TeoS
Checking on this page , found this :
According to them , the amp wouldn't be powerful enough to drive corectly the 612 . On the other hand , almost all the posts found on the net by me say the amp has excessive power(volume) and some state that the hifiman is one of the best match for the k612 Pro ...
A bit confusing...
On the other hand , synergy is not about power (only)
The output power of EF 2A into a 120 Ohm load is an estimation. The amp is rated ar 32 Ohm and 150 Ohm. I haven't found measurements of that amp with that exact load.
Based on specs, with an output of 4V, K612 will reach -approx- 113dB, that's a safe mark to claim that the amp is capable of driving the headphone. EF 2A is capable of 6,2V into 150 Ohm so it won't have any trouble with 4V at 120 Ohm.
I'm yet to find what synergy really means, but it's true that power is not the only important factor to determine how good an amp can drive a headphone. The output impedance has to be considered too. I'm still not sure about the EF 2A output impedance. In the specs of EF 2A in the HIFIMAN's web page says:
Output Impedance: 32-300 Ohm
(Variable output impedance?) That sounds quite rare to me but it could be possible.
For your headphones, to preserve the frequency response you need an amp with an output impedance under 15 Ohm, otherwise the damping factor is quite too low and an important part of the amp's power is not capable of reaching the headphone, so the amp may act as a less powerful amp no matter its specs.
If you can find more info about EF 2A's output impedance, it would be much safer to use its specs to know how much power it could drain into your headphones.