HELM DB12 AAAMP Mobile Headphone Amplifier, THX AAA Technology, Analog Amplifier, 12 dB Signal Boost,+6 dB Bass Boost, THX Certified, Male 3.5mm to Female 3.5mm Audio Jack

I really like this amp. I use with Sennheiser HD 599 headphones. It has made listening to streaming services on my phone sound as good as listening through my home sound system. I've always had my phone volume maxed and now it's just over three quarters up. I like the small in line shape and fuss free control. I didn't want an amp that was awkward to carry this just looks like part of your headphones.I have also used with PS4 controller, it takes the volume to a much better level for me. The volume control buttons cannot adjust the PS volume.There is a short charging cable supplied but I use a longer (Samsung) type C USB cable. There is zero affect on sound quality if you charge whilst listening.

Feisty little thing! Does the job admirably. Volume buttons do not work when connected to Xbox Series X controller but minor. Would have preferred if it was powered by an AAA battery that way I can replace it; instead battery is integrated and so needs charging. I am expecting the battery to loose its potency in a few years, ah well can't have it all!