On power: 64 of the 65 audio interfaces here reach 100 dB SPL on the AKG K612 Pro. It needs 6.6 mW at its 120Ω, and 1 of them do not get there.
Power is one of three questions and the one that goes wrong least often. The other two — whether the source’s output impedance leaves the frequency response alone, and whether you will hear its noise floor — are answered further down, separately, because a source can pass one and fail another.
The 1 that fall short are Steinberg UR22C. The closest of them, the Steinberg UR22C, delivers 5.0 mW into 120Ω against the 6.6 mW needed — 1.2 dB short.
The cheapest one that does reach it is the Zoom AMS-22 at $100, which delivers 7.4 mW into 120Ω — 0 dB of headroom over the 6.6 mW this headphone needs for 100 dB SPL.
100 dB SPL is a peak level, not a listening level. If you listen at 85 dB the same headphone needs 0.21 mW, which is 15 dB less, and the answer above changes for most of the category. The model page has the full ladder.
Under the one-eighth rule the AKG K612 Pro wants a source below 15.00Ω. Of the 43 audio interfaces here that publish an output impedance, 29 are under it and 14 are not.
The furthest over is the Tascam US-2x2HR at 66Ω, which is 4× the ceiling. Above that threshold the source stops being a volume control and starts being part of the frequency response. The simulator shows what that looks like.
The other 22 publish nothing at all on this, so they are not on either side of that count. This site leaves them blank rather than assuming a figure.
Hiss depends on the source’s own noise floor and on how sensitive the headphone is. At 91.8 dB/mW and 120Ω, the AKG K612 Pro turns one microvolt of source noise into about -19 dB SPL — and the threshold where that stops being noticeable in a quiet room is around 20 dB SPL.
Of the 4 audio interfaces here that publish a noise figure, 4 stay below that threshold with this headphone and 0 cross it.
The remaining 61 publish no noise figure, so they cannot be placed on either side.
| Source | Price | Into 120 Ω | Headroom | Output impedance | Hiss in these |
|---|---|---|---|---|---|
| RME Babyface Pro FS | $899 | 100 mW | 11.8 dB | 10 Ω | -3 dB SPL |
| RME ADI-2 DAC FS | $1399 | 320 mW | 16.9 dB | 0.1 Ω | -12 dB SPL |
| RME ADI-2 Pro FS R | $2199 | 792 mW | 20.8 dB | 0.1 Ω | -12 dB SPL |
4 of the 65 audio interfaces here publish all three figures. 4 of those clear all three for the AKG K612 Pro, and the cheapest is the RME Babyface Pro FS at $899.
It delivers 100 mW into 120 Ω where this headphone needs 6.6 mW for 100 dB — 11.8 dB of headroom — its output impedance of 10 Ω sits under the one-eighth ceiling of 15.00 Ω, and its 6.3 µV of noise leaves the hiss 23 dB under the 20 dB SPL threshold this site uses.
Cheapest that satisfies three published numbers is not the same as best, and the sources left out of this count are left out for want of a published figure, not for failing one. How often that happens is its own page.
| Source | Price | Into 120Ω | Output impedance | Hiss in these | Power verdict |
|---|---|---|---|---|---|
| Audient iD4 MkII | $199 | 86 mW | not published | not published | Comfortable |
| MOTU M2 | $219 | 89 mW | not published | not published | Comfortable |
| SSL 2 MkII | $229 | 100 mW | 1 Ω | not published | Comfortable |
| MOTU M4 | $279 | 89 mW | not published | not published | Comfortable |
| PreSonus Studio 68c | $299 | 70 mW | not published | not published | Comfortable |
| SSL 2 Plus MkII | $299 | 100 mW | 1 Ω | not published | Comfortable |
| Audient iD14 MkII | $349 | 86 mW | not published | not published | Comfortable |
| IK Multimedia AXE I/O | $400 | 75 mW | <0.1 Ω | not published | Comfortable |
| MOTU M6 | $499 | 89 mW | not published | not published | Comfortable |
| SSL 12 | $599 | 315 mW | 1 Ω | not published | Comfortable |
| Apogee Duet 3 | $649 | 315 mW | 0.5 Ω | not published | Comfortable |
| MOTU UltraLite-mk5 | $699 | 126 mW | 1 Ω | not published | Comfortable |
Sorted by how many of the three questions the source answers well, then by price. A blank in a column is a blank in the manufacturer’s own documentation, not a zero.
The AKG K612 Pro on other categories: USB dongles · portable players · desktop amplifiers.
The AKG K612 Pro page has every source in the database against this headphone, and the matcher takes your own numbers.