I am a bass player and I would like a clean boost, simple to use. I have two basses with different output and I would like to get the same level at the end. Therefore, I want to ask you if the Spark Mini Booster colors the sound in any way or if it just simple level boost? Does it works well for bass too?
The Spark Mini Booster will not change the original tone of your sound. However this is depending on where the pedal is located in your signal chain. I will expand on this point later on.
The Spark Mini Booster like the Spark Booster (standard box) it is a clean boost. On the Spark Booster you get more settings like gain and tone controls for bass & treble. The gain control can add some overdrive to the sound. Useful for guitar players. Bass and treble knobs have neutral point at noon. For middle control frequencies, you have a 3 position mini toggle switch, clean is for neutral.
On the Spark Booster (standard box), set all tone controls to neutral. Middle toggle switch to clean position & gain knob all the way down. Setting it like this will give you the same settings as the Spark Mini Booster: a neutral signal booster with 20dB boost capacity.
There will be no coloration on your sound especially if you use it at the end of your signal chain (after pedals) or better, if you put the pedal in the FX loop of your amp. This will be the best way to use it in order to obtain what you want, have the same output level with your both basses.
Finally, yes it will work great for bass and it is a great choice because the Spark Mini Booster is simple to use and you probably do not need overdrive (gain knob) which is on the Spark Booster (standard size). Please check it out at your favorite dealer, you won't be disappointed.
Spark Mini Booster product page
Please see the Spark Mini Booster user manual
On this FAQ you can learn more about differences between Spark Booster and Spark Mini Booster