The Aguilar OBP-1 is without question the best active circuit available for the bass. The key to its great sound is that it is a shelving style, boost only pre-amp that sounds more like a loud passive system than a hi-fi active one. Set to the off position, the EQ is flat with a lot of midrange. As the bass and treble is turned up, the midrang goes down in a natural fation that balances out perfectly. It is a loud pre-amp, so I would recommend using the input buffers on the input of your amp, if present (-10db and -15db are the most common). This the most natural sounding system I have ever heard, but it is also a noticeable up-grade to any other active, onboard bass pre-amp on the market, so you will notice a boig difference. If youn do not want to rush into installing one on your bass, there is also an outboard version you can try. Mine was a cost extra option on my Modulus Flea Bass Five string, resulting inthe most incredible instrument I have ever owned, and I have over 22 years of Bass playing in bands under my belt along with many High end basses, including another Modulus Flea without the Aguilar OBP-1. The OBP-1 is truly a work of practical art.

I put this in a custom made bass with two DiMarzio Model One humbuckers. The OBP-1 seems to broaden the spectrum of sound from the bass, increases headroom, makes the bass considerably louder and hotter (that's pickup dependant, I'm sure) and simultaneously adds warmth to the mids and bottom as well as a crispness to the highs. It's a drag to install, though Aguilar has diagrams for many pickup configurations on their site. It's also 18 volts, which means two batteries, so you need a pretty big cavity. The effect is great, though - I have not even touched my EMG P/J Precision since getting this preamp.

Installed the OBP-1 in a Peavey Foundation 5-string passive bass with single-coil pickups. Added LOTS of punch down low, and bell-like treble. A HUGE improvement in tone quality and range!