[Battery] I use to as a headphone interface to a guitar tube amp DI out. It works great for that.

[Single Channel] I was really pleased with how loud the amplifier was. It was able to power even 80 ohm dt770's with enough volume to use as a monitor for a drummer during a live music session. My only grievances are it's pretty large so wearing it via the belt clip is awkward and the printing on the power adapter says it requires a 9V center positive adapter when in reality it requires a 9V center negative adapter. In a way this is actually way more convenient because most dc 9v adapters are center negative.. but it was a little annoying because I ordered the indicated adapter which didn't work so I then had to trace the board to figure out that mistake.. Hopefully they fix this error at some point but otherwise it's a great product.

[5 Kilohms ] I was looking for a micro amp to mix our stage monitor signal with my mic or guitar/bass -- so I could add a bit more of me in my headphones. This works great. Has both sizes of headphone jacks, a choice of mono or stereo, separate monitor and mic/instrument volume controls, and XLR in and thru for live mixing. Also has a ground lift, which can be a difference-maker when you have house line noise. I use it mostly for adding my bass to the monitor mix. Small enough to fit on my pedal board, so it just comes along with me all the time now. The only caveat: The XLR inputs are low-Z, so you'll need a DI box to connect instruments. However, that is easy to work around considering all the other benefits.

[2x AA] I’m a drummer and I need something that will be audible clearly even with a loud instrument such as a drum set.

Even though, this is enough already for monitoring purposes, which is not critical as far as noise (Hissing) goes, this device happens to have NO noise, no hissing whatsoever.

If whatever source of audio you plug in, and there is hissing, humming etc, it’s your “whatever” that’s causing the issue. This unit not only has clean audio, but it’s LOUD. So loud that will satisfy anyone but will damage your ears if you’re not careful. If you want LOUD, the Polsen PMA-2B will deliver.

To use it from a mixer: simply run a pair of XLR OUT cables from the mixer to the PMA-2B. Try to keep the levels from your mixer not to exceed 0db and no EQ for the best and cleanest sound.

I also like the many ways to attach this unit. It has a belt clip, a solid 3/8 mount plus a shoe mount!
To use you iPhone as the source since it doesn’t have XLRs:

But this cable:
Stereo Male XLR to Stereo Male 1/8” TRS. (Assuming you have the Apple lighting adapter) and you’re done! And again, it’s plenty loud.

I only wish the PMA-2B had those dual purpose XLR female inputs that accepts either XLRs or Mono TS plugs (each channel) for even more versatility when XLR is not viable.

Overall, price is right, ALL METAL, good electronics, no hissing and it’s LOUD. What else could you want?

I’m pretty happy with mine.

Also, check out the images I provided on my reviews. They can be useful to you.

[I have received this product in exchange for my honest review].

[0.675 lb] My Steinberg audio interface cannot drive the 32-ohm Yamaha on-ear headphones I like to sufficient volume. Putting this device between the Steinberg and the headphones gives a more-than-sufficient volume boost huge excess headroom; it could probably power way higher-impedance phones than mine. It's probably not audiophile-level sound, but for my purpose (hearing myself during self-recording) it's fine. The build quality seems good, and I like that I can switch the phones from mono to stereo. I don't make use of its other features, like mic monitoring/mixing.

[Battery] The unit is very functional and appears to be well-made.

[Single Channel] Replaced my Behringer with this and this unit performs great!

[5 Kilohms ] Studio or Live ,you can't go wrong with this little beast.