Universal Audio Twin Finity combined tube/transistor mic preamp
Although some will say that it is best to capture a very accurate sound on recording, and process it later any way you like, there's a certain magic in getting exactly the 'right' sound at source. In general, transistor preamps provide all the accuracy anyone could want (providing the mic is accurate too of course), and vacuum tube preamps give a kind of warmth that is difficult to achieve any other way.
So why not have the best of both worlds? The Universal Audio 710 Twin-Finity Tone-Blending Preamplifier & DI Box (to give it its full title) seems to do just that. It combines a transistor preamp with a completely separate tube preamp, and blends the two together, controllably, into a single output. So you can have the transistor sound (which is actually no 'sound' at all), the tube sound, or anything in between.
One problem however is that to get exactly the right sound, you have to know what you want beforehand. This takes experience. It would be quite easy to undercook or overcook the warmth. Then you're stuck with what you have done for the rest of the recording process all the way to mix and master. (You could add extra warmth by other means if you wanted to, but that would seem to negate the whole point of the unit.)
And this is where the Twin-Finity gets it totally wrong. Rather than blending the outputs of the two preamps into a single output on the rear of the unit, there should have been two outputs - one for the transistor preamp, one for the tube. They could have been recorded onto two tracks and the blend could then be adjusted at any later point in the recording process.
Still, it's an interesting device and it is always useful to have more tone colours to play with. And Universal Audio should be applauded for their innovative thinking.