See the "optional power amp available" in the picture.
[Blocked Image: https://fbcdn-sphotos-f-a.akamaihd.net/hphotos-ak-ash4/280962_586539894695671_1385047946_o.jpg]
And this...
[Blocked Image: https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-prn1/36525_586501518032842_416812621_n.jpg]