Phil Jones Double Four Plus BG-80 RD

I was looking for a lightweight combo amp through which to play my double bass, fitted with a Realist Copper Head pickup, and read some good reviews of this amp (albeit from bass guitarists). It certainly is very lightweight and portable (it fits really well in an Accu-Case AC-115 Soft Bag). I was impressed by the claims made about the very small speakers and the power (90 watts, apparently). However the reality for me was intense disappointment - using the amp without a pre-amp resulted in a lot of distortion at not very high audible volume. With a pre-amp (Fishman Platinum Stage) I could get some distortion-free sound but the volume remained low.
I thought this amp would be a more portable and more powerful alternative to the Harley Benton AC60 pro - it is lighter but that's it. This amp is also extremely expensive for what it is. I thought that at that price I'd be getting quality equipment that fits my needs but it doesn't. As I'm playing an acoustic double bass, I don't need an amp to practise alone. I need an amp to practise with a small combo and this doesn't really add much to the acoustic sound of the instrument in terms of volume before it distorts.
I don't know how this works with a bass guitar (for which it was designed) so only take my comments onboard if you're looking for an amp for a double bass.