A quick introduction about me first. I am a designer who builds experimental and portable sound systems. I have nothing to sell (at the moment), but have managed to get my hands on one from the first production run of the Vamp, which is a product that sits right in my field of interest, so I thought I would share my thoughts. I have pictures, but am unable to load them as this is my first post.
In the interest of full disclosure, I am not associated with Paul Cocksedge (designer of the Vamp) in any way, although I did attend the same design college some years after he graduated.
So the Vamp is a small amplifier with a battery and Bluetooth receiver built in, powered/charged via usb, all wrapped up in a little rubberised cube with a corner lopped off. The idea is that you can attach it to "any" speaker and turn into a portable sound system. Great idea, mainly because I believe the speaker is always the most crucial bit of the sound system, and there are cheap, high quality speakers around on the 2nd hand market for little cost. It caused a minor Kickstarter storm and achieved its funding target in no time at all.
I had reservations about the Kickstarter video because it was obviously aimed at non-technical people, which is fine, but presented in a way that, without a bit technical knowledge, you might have unrealistic expectations of the product, which isn't so fine.
Tech limitations - USB has a maximum power output of 5W, and lithium batteries a nominal voltage of 3.7V, 4.2V when fully charged, so you are never going to get huge power out of it. They claim 4W power output, but that is probably at 2ohms, with 8ohm speakers (most common) you'd be lucky to get 2W.
So I hooked it up to one of my big 8 ohm Tandberg Studio Monitors, bluetoothed to my phone, and was quite surprised how decent a volume level you could get. It is enough for listening at home, but not house party material, and outside (where everything sounds 4 x quieter) you might struggle against ambient noise .
It sounded a bit harsh and thin, with no deep bass, but listenable. After a while I tried the wired connection with the provided USB to headphone adapter, and it sounded a whole lot better, suddenly there was some depth and clarity, but it obviously struggled a bit with the volume turned up, but much better than expected.
Next test was with some little JVC 4 ohm speakers that I use for lots of projects. Bluetooth sounded subjectively louder, presumably because the Bluetooth had eaten all the bass and so the little amp was off the hook to a certain extent. I even tried 2 in parallel as a 2 ohm load and it seemed stable, and this configuration will make the most of the power available. With a wired connection it seemed quite noisy when running off my laptop, and weirdly, quite distorted at very low volume.
Next up a little 8 ohm Quadral speaker, which I know is not very sensitive, and sure enough, this is where the Vamp really struggled, distortion coming in at quite low levels.
So as for the "use any speaker" claim, well, sort of, but some speakers will work much better than others. You want high sensitivity, and low impedance to get the best out of it. In practice that means large or quite tinny sounding speakers.
Next I compared the sound of an Avantree apt-x (newer Bluetooth audio standard) wireless audio sender, and it was much better than the built in Bluetooth. Use a wire with the Vamp if you can.
Battery life has been impressive; 2 hours before the low battery light, and another hour at low volume.
Better than expected, quite usable and nice sounding with the right speakers. A great way of making a flexible low power, mono, low cost sound system.
Non APT-X Bluetooth sounds rubbish, so use the wire if you can.
Don't go thinking it is ticket to impromptu outdoor raves. It is for moderate sound levels in quiet places.