This is a portable headphone amplifier for bass guitars. It features built-in compression and volume control and includes auxiliary stereo input and output for playing along with music. Mid and treble boost modes are available for tone shaping and the unit can be powered by a 9 volt battery or a power adapter. The power adapter is not included but I did just replace the battery with a fresh Energizer Max 9V. The battery compartment is clean... no corrosion.
I just added a video showing me testing the unit. I hooked it up to my son's old green Mr. Potato and everything seems to be working perfectly. I noticed that many of the units sold online came with headphones, so I'll even throw in a brand-new pair of Kenwood headphones. These came with a portable CD player my brother bought years ago. He did use the CD player in his car, but he never used the headphones.
Please look at the pictures carefully and ask any questions you may have before bidding or buying. What you see is what you get.