The Boss VB-2 is a vibrato pedal which came out in the early 80s. It was the first primitive Whammy bar pedal of its kind which can mimick the vibrato-arm of a Stratocaster.
Among the controls are a Rate, Depth and Rise Time control. The Rate knob controls the speed of the vibrato, the Depth control makes the effect more noticeable. The Rise-Time can be applied when the effect is in Unlatch mode (more about this later) It controls the time for the effect  to come on when the pedal is being pressed down. This control is very subtle. On the whole the VB-2 is a primitive pedal, but used in the right way, it can be a very effective and creative tool. The effect can be switched on to be used at all times (like any standard Boss pedal) or it can be applied when being stepped on: Use the Unlatch mode and keep pedal pressed down to apply vibrato effect, once you take your foot off the pedal, the vibrato effect will be gone. Using the the VB-2 in this manner is great for mimicking vibrato-arm effects on chords or phrases or bends. There is a bypass mode, in this mode the signal is being bypassed without the VB-2 still being in the signal path.
The pedal does use a Boss ACA powersupply, when the pedal is daisy chained with other effects you are able to use a Boss PSA powersupply.

Comparing the effect with a Tremolo unit, the VB-2 is more crude and fuller in sound.Most Tremolo effects (or amplifiers) use variation in volume to obtain the Tremolo effect. The VB-2 uses variation in pitch, hence the pedal being more crude and less subtle in sound compared to a Tremolo effect.

The Vibrato effect is obtained in the VB-2 by varying the pitch of the sound: The pitch of your original sound goes down first before it comes back up again therefore it is possible to mimick the sound of a guitar with a vibrato arm first being pressed down before it comes back up again. Sounds which mimick the vibrato arm just holding up-or down are not possible. The VB-2 will always return back to original pitch, and this may be one of its limitations.

Guitar Players who use the vibrato-arm of their guitar regulary will enjoy using the VB-2. The VB-2 does not have to substitute your vibrato- arm, you can use it happily along with your vibrato-arm to create some extra vibrato effects.
Do not have a guitar with a vibrato-arm? No worries, the VB-2 may do the job of giving you the idea that you are using a guitar which does have a vibrato-arm.
Want any dive-bombing? The VB-2 may be a bit limiting on this side, the Boss PS-5 or PS-6 may be a better choice for you.

Happy Pedal Hunting.
Eddie