Markbass Compressore: This tube comp is a new pedal from an Italian brand known for their amplifiers. First, I must say it has almost no noise! Even at high compression settings the noise is low, which is amazing for a tube pedal. The tone is very smooth and clean, not very colored by the tube, although it does seem to add a nice "thickness" to the mids. There is no loss of lows, and the low end sounds big and full. The useful highs are not rolled off, but the upper end is kind of "dark" sounding, as though the very highest frequencies may be cut off. Also under heavy constant compression, the tone can get muddy. But under normal use it is clean and articulate. The action is quite smooth, and has a remarkable range: both from gentle to limiting, and from "invisible" to a very funky squashed effect, all found with different threshold and ratio settings. It has a full range of controls, and each of them is quite effective.
It can handle any instrument level of signal you can throw at it without distorting. It does a pretty good job as a peak limiter, although if you hit it with a strong spike over the threshold, the signal will "dip and swell" noticeably, which some people might not want. This can be avoided with a higher threshold or less extreme spikes in your playing, or you can use it as a cool funky effect.
Another remarkable thing about this pedal is that the tube itself actually performs the compression. In most other so-called tube comps, the tube they use is just a gain stage following a solid-state (usually optical) compression element. You typically only see "true" tube compression in high-end and vintage studio processors. I think the use of the tube as the compression element, instead of just a gain stage, contributes to the low noise and uncommon action of this pedal.
To access the tube you have to undo six screws and three nuts. The construction is very rugged, and the footswitch is true bypass.
There are two downsides: One, this unit is quite large--about the size of the Ashdown and Trace Elliot pedals, slightly bigger than two standard Boss pedals side by side. Two, it requires a 12 VDC power supply that can supply at least 500 mA current (very typical for tube pedals). However if you can live with those drawbacks, then this comp is pure gold. I would put it up against a high-end rack unit any day.
I A/B compared it against the T-Rex Squeezer, which is a direct competitor since it costs a similar amount, has one tube, has the same controls, and uses exactly the same power supply. The tone of the T-Rex is brighter in the highs, while the Markbass has fuller mids. The T-Rex has some extra hiss, while the MB is remarkably quiet. The T-Rex is much smaller, but not as ruggedly-built as the MB. I also A/B'ed it against the Maxon RCP-660, which is another tube comp pedal; the Maxon has brighter highs and a more tube-colored tone, but the MB is superior in every other way. I like this Markbass pedal a lot!