Aguilar:

"OBP-1" Two band, broad shelving +18 dB at 40 Hz and 4 KHz.
Dimensions: .6" x 1" x 1"

Alex Aguilar's two band on-board preamp sounds great and is veryquiet. It a boost-only circuit, starting from unity gain. It's designis reminiscent of the old Sadowski preamp.The 18 dB of boost requiresplenty of headroom, 18V is recommended. The circuit can handle9-48V. It comes with separate bass and treble controls however an EMGdual stacked volume pot* can be used if stacked controls aredesired.

Bartolini:

This is Bill Bartolini's latest and most refined design. It isquieter and more transparent than anything else out there (108 dB S/N,THD .003% @ 100Hz) and really sounds good. To quote from the specsheet "The (bipolar) +9V/ -9V system allows a completely DC coupledsignal path. There are no capacitors to diminish in any way the lowend punch, clarity and frequency response of the instrument". Bill hasused wide bands that overlap slightly to avoid the honky sound ofother midrange controls. The 250Hz mid could be useful as a cutoption when recording. Includes a gain trimmer to match output withyour other axes. There are several things to be aware of, the controlsare passive without separate gain stages, there is some interactionbetween them (ie when you boost the low the mid gets boosted a bit aswell.) The circuit is flat well into the subsonic range so that youmay find your speaker excursion wasting much of your amp's powerunless you filter out below 30Hz. The circuit shifts phase by 180degrees which simplifies active/passive switching using a push pullpot. there is a tiny offset voltage with the bass boosted which alwaysgives a "Thunk" when you switch between active and passive unless youturn things down first.

*note: Bartolini on-board preamps now operate at 9 or 18 voltsand are no longer dual rail (+9V/-9V) [M.S.]

EMG

I have used dozens of these in basses, they work well, theyare easy to install and are reasonably quiet (96 dB S/N). They don'tmake your bass any better sounding though. The treble shelving isswitchable from 2500 Hz to 3500 to 4500 to 8000Hz via two microswitches inside the bass. It's a pretty impractical feature that'shard to evaluate.

Cool but unacceptably noisy, the mid band is a bit too narrow to beuseful except as an effect on fretless. You can make wah-wah soundswith your free hand...

E-PRO

"U-RETRO" - 3 band EQ system with a sweepable mid, dual inputbuffers and adjustable gain from 1 to 12 dB for eachpickup. Dimensions: 0.4" x 1.3" x 2.75"

Includes stacked volume and blend controls (blend only works inactive mode), asymetrical treble control with center detent - (+12dB @3kHz, -12dB @ 1kHz ) which can be pulled up for "bright" (+8dB @7kHz), stacked with boost only bass control (+15dB @ 50Hz).> Midcontrol; (+/- 12dB) indent at "flat" setting, stacked with frequencycontrol - (150Hz-3KHz). Also includes active/passive switch and pickupselector switch for passive mode (switches between rear pickup andboth pickups together). Uses custom plastic element pots, 3 ICs andcompact, low noise components on a single epoxy insulated board. 18Vpower.

Very cool but still quite noisy. It colors the sound -treble getsmuted, -bass is bigger and tighter. John is redesigning the circuit toimprove the noise ratio and flatten out the response. Oh, also themost expensive unit I know of at $250

Note from David (7/2004):
The E-Pro preamp has been completelyrevamped since the one I tried and John has addressed all the issueslisted above. I haven't had the opportunity try one since the redesignand can't comment first hand on the new unit.

Lane Poor
(Out ofproduction)

"2 AC" Variable10 dB boost with dual buffer, battery checklight, 9V supply, 3 band eq insert point).
Dimensions: 0.5" x 1" x2.25"

The latest design with ultra quiet, audiophile chip andtrimmers for each channel allows you to set boost independantly. UntilWAM starts production of his 3 band EQ section, this unit is probablysuperfluous unless you need a buffered blend and variable boost

MØRCH

Concentric bass and treble with center detents, 18dB boost,6dB cut, switchable mid boost
Dimensions: 0.5" x .6" x2.6"

I have had this circuit in my bass since the mid-eighties andit is different from most others in that the shelves are wider and theslopes flatter. I like it because it really does something withoutmessing up the volume balance between the strings, when you boost thebass you're boosting everything between 20Hz and 300Hz instead of say40Hz to 60Hz as in many circuits. If I need to fine-tune my sound I'drather do it on my amp anyway. Hand soldered with high grade,discrete, components using only 2 transistors so noise should beminimal though I have experienced some RF interference. The circuitcan be powered with 9V to 48V, I use 18V.

Seymour Duncan

I like these now, they work well, The lows are frightening, (MM lows are probably too low). They have a push/pull volume switch that activates a "slap contour" which you preset inside the bass, giving you two distinct sounds. The noise floor is low at -85dB according to the specifications. The bands are narrow and preset; bass is centered at 30Hz (25Hz on the Music Man model), mid is 675Hz and treble is up at 6800Hz. The rather large circuit board uses SMT components and bulky, plug-in connectors to make it a tricky retrofit (the Music Man version is smaller). Can not easily be by-passed as you would need to add a passive volume pot. Runs on 9-18V.