LD Systems HPA 4

This headphone amplifier does a pretty good job for it's price.
It can provide enough amplification for pretty much any kind of headphones.
The build quality is decent, but far from good.
The volume knobs have an uneven rotation and only the 1st out of the 4 present has some sort of tactile feedback on each step from 0 to 10 (min to max).
It generates noise, specifically from 50% volume and up, on each of every 4 outputs. Fortunately, for just tracking vocals/instruments this is not much of an issue.
What is an issue, at least in my opinion, is the fact that due to the way they were engineered (confirmed by the manufacturer) there are very loud pops and clicks whenever you connect any pair of headphones on any of the 4 outputs, both at minimum and maximum volume... This is definitely something that makes me think twice any time before I plug in any of my rather expensive headphones and if possible, I avoid to do this because I would totally hate to damage them.
The customer support of LD Systems, even if they are labeled as a b2b service and I am just an end user, was very supportive and replied to the questions I had very fast and in a friendly manner. They also told me that the pops and clicks "should not be damaging" for the headphones, but I still have my reserves about this.
Conclusion, if you need a cheap and fast solution you can go for this product. If feels sturdy, due to the metal casing, but expect no "high end" build quality of functionality. Also, make sure you don't wear your headphones when you connect them to the amplifier, as your ears might hurt due to the pops/clicks that happen every single time when you connect the headphones. If you let your headphones connected to it and you leave it plugged in (there's no power on/off switch), this shouldn't be an issue.