ART HeadAmp4
4x Workhorse amp in one Package
ART makes a variety of studio and stage gear. Among DI-boxes, mic-preamps, mixers and power amps, they also make some headphone amps, like the Headamp4.
Construction & Overview
As part of their ARTcessories-series, the case is built to stack with a variety of other devices.
The Case is built from an aluminium extrusion with front and back plate screwed on. While I wouldn’t use it as a step ladder, it will be fine when falling off the back of a rack or sliding off a desk.
The feet are rubber bumpers that can in theory be torn of. I have never seen that happen on any ART-product of this type though.
Word of warning: These feet will stain wood and flight cases when left sitting on them.
The front has a green power LED and 4 volume knobs.
In the back is where the 4 knobs (and the name) get confusing:
5 1/4" (= 6.3mm) and 5 1/8" (= 3.5mm) jacks present themself clearly labeled.
With this amp, you and your 7 closest friends can all listen to the same song using headphones (assuming you can form pairs of similar impedance… 
)
Features & Specs
Full Spec sheet
The Headamp4 has no power switch. Maybe a pain at home, prevents someone from accidentaly turning it off though.
All inputs (and outputs) are TRS-unbalanced.
The high output impedance of 47 Ω (per channel) indicates this is not meant for home-gamer 32 Ω or 16 Ω headphones.
The 91k Ohm input impedance allow to chain multiple of these together (the 3.5mm and 6.3mm jacks are in parallel) without dragging the output of the mixer (or Audio Interface) too low.
Enough of me rambling:
Review
I had this thing for a little over two years now. I originally bought it because I used one before for monitoring and “familiar and robust” beats any raving review
Mine got yanked off my desk twice, once to hit the floor and once to be caught by the cables, there are no scratches in the paint yet!
The case is solid, the knobs are solid, the jacks are solid.
Only gripe is the barrel jack. A screw-in variant would be preferable.
All 4 potentiometers run super smooth in feel and audio. The knobs are perfect, clear indicators (readable in the light the power LED puts out), good texture and size.
Sound
As hinted at above, this amplifier will “run out of steam” with low-impedance or inefficient headphones. The bass falls of a cliff and treble will come forward.
DT-770’s (80Ω and 250Ω) are fine, HD-25’s are fine, PortaPro’s are fine (might want to bring an extension cable though), M40x work okay-ish. I would guess the AKG K-2x0 / K-2x1 series to be fine too.
Hiss becomes audible around 12 o’clock, after 2 is unusable. As said above, the potis are perfect and channel balance is spot on right from 0.
Compared to my LakePeople G103-s details are not as good, bass is slightly less pronounced and treble smoothed over a bit.
Look inside
There are two PCBs inside, one “passive” one with the Power LED and 6.3mm jacks and one “active” one with potis, Op-Amps and 3.5mm jacks. They are connected via single row pin and socket connector.
I think the silk-screen printed ART-logos are a nice touch
The active board has a spring to provide chassis grounding and a diode to prevent reverse polarity on the barrel jack from frying the device. Input buffer and headphone amplification is provided by JRC 4580 Op-Amps. These are meant for audio and specifically headphone amplifiers.After the 47Ω resistors, the output is then capacitor coupled to the outputs.
Verdict
The ART HeadAmp4 is a “no thrills” workhorse for monitoring or other applications that require a solution that works and lasts. At 80€, sound is nothing to write home about.