I was able to compare a few amps. I have a 90 year old massive bass and use the vektor pickup (built-in version).
The amps I tested were:
Genz Benz Shuttle 3.0-10T
Genz Benz Shuttle 3.0-8T
Markbass Minimark
Schertler Unico
SR Tech Jam BB 150
SR Tech Jam BB 300
AER Bass One
The amp I owned before was the Gallien Krueger MB150E-III. I was never content with the sound. First of all, I have to say that all of the mentioned amps delivered a better sound than the GK.
The Genz Benz combos are neat combos and certainly unbeatable for size and weight. I liked the 8 inch version more as it was less muddy, more transparent. Only the low E was a little bit weak, but still with that, the combo delivers a usable sound.
The Mark Bass Minimark had no problems with the low E and had overall a more defined and likeable sound. The downside with this amp is the missing EQ. Somehow, the filters don't change the sound very much (they work well with electric bass).
Next I compared the Schertler Unico and the SR Tech Jam BB 150. The Jam BB 150 is not intended to be a bass amp, it rather is an active box with 8" speaker and 6 channel mixer (look
here. I didn't like the Schertler Unico very much, but the Jam BB 150 was just great. Unlike most bass amps, you get all frequencies your instrument delivers. A nicely defined sound with beautiful lows, transparent mids and tickling highs (or so). And all that for a reasonable price.
The SR Tech Jam BB 300 is basically a bigger version of the Jam BB 150 especially designed for double basses, cellos and fretless basses. The sound is as great as the little brother, only more powerful.
The last combo I tested was the AER Bass One. This is a electric bass amp, but from the mentioned electric bass amps, it was certainly the one with the most linear and transparent sound, yet not as linear and transparent as the SR Tech amps. It doesn't deliver all the high frequencies the SR Techs delivers. It sounds a little bit compressed compared to the SR Techs (and I'm not talking about the built-in compressor). But it is also more powerful. I don't think that either of those two amps sounds better than the other, it's just the question if you want a very transparent hifi sound with lots of highs or if you want a tight and powerful sound.
The reason I finally decided for AER was that the sound of the AER stays transparent even with high volumes, while the SR Tech tends to emphasize frequencies that might be problematic to deal with in some situations. Of all the mentioned amps, the AER was by far the best for electric basses.
