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David King, Bass Guitar
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"OBP-1" Two band, broad shelving +18 dB at 40 Hz and 4 KHz. Dimensions: 0.5" x 1.4" x 2.25"
Alex Aguilar's two band on-board
preamp sounds great and is very quiet. It a boost-only circuit,
starting from unity gain. It's design is reminisant of the old
Sadowski preamp.The 18 dB of boost requires plenty of headroom, 18V
is recommended. The circuit can handle 9-48V. The unit is
encapsulated in an awkward size case that can make it difficult to
retrofit. It comes with separate bass and treble controls however an
EMG dual stacked volume pot can be used if stacked controls are
desired.
Bartolini:
This is Bill Bartolini's latest
and most refined design. It is quieter and more transparent than
anything else out there (108 dB S/N, THD .003% @ 100Hz) and really
sounds good. To quote from the spec sheet "The (bipolar) +9V/ -9V
system allows a completely DC coupled signal path. There are no
capacitors to diminish in any way the low end punch, clarity and
frequency response of the instrument". Bill has used wide bands that
overlap slightly to avoid the honky sound of other midrange controls.
The 250Hz mid could be useful as a cut option when recording.
Includes a gain trimmer to match output with your other axes. There
are several things to be aware of, the controls are passive without
separate gain stages, there is some interaction between them (ie when
you boost the low the mid gets boosted a bit as well.) The circuit is
flat well into the subsonic range so that you may find your speaker
excursion wasting much of your amp's power unless you filter out
below 30Hz. The circuit shifts phase by 180 degrees which simplifies
active/passive switching using a push pull pot. there is a tiny
offset voltage with the bass boosted which always gives a "Thunk"
when you switch between active and passive unless you turn things
down first.
I have used dozens of these in
basses, they work well, they are easy to install and are reasonably
quiet (96 dB S/N). They don't make your bass any better sounding
though. The treble shelving is switchable from 2500 Hz to 3500 to
4500 to 8000Hz via two micro switches inside the bass. It's a pretty
impractical feature that's hard to evaluate.
Cool but unacceptably noisy, the mid band is a bit too narrow to be useful except as an effect on fretless. You can make wah-wah sounds with your free hand...
"U-RETRO" Britain's John East has designed a state-of-the-art 3 band EQ system with a sweepable mid, dual input buffers and adjustable gain from 1 to 12 dB for each pickup. Includes stacked volume and blend controls (blend only works in active 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). Mid control; (+/- 12dB) indent at "flat" setting, stacked with frequency control; (150Hz-3KHz). Also includes active/passive switch and pickup selector switch for passive mode (switches between rear pickup and both pickups together). Uses custom plastic element pots, 3 ICs and compact, low noise components on a single epoxy insulated board. 18V power. Dimensions: 0.4" x 1.3" x 2.75"
Very cool but still quite noisy. It colors the sound -treble gets muted, -bass is bigger and tighter. John is redesigning the circuit to improve the noise ratio and flatten out the response. Oh, also the most expensive unit I know of at $250
"2 AC" Variable10 dB boost with dual buffer, battery check light, 9V supply, 3 band eq insert point). Dimensions: 0.5" x 1" x 2.25"
The latest design with ultra
quiet, audiophile chip and trimmers for each channel allows you to
set boost independantly. Until WAM starts production of his 3 band EQ
section, this unit is probably superfluous unless you need a buffered
blend and variable boost
(Concentric bass and treble with center detents, 18dB boost, 6dB cut, switchable mid boost.). Dimensions: 0.5" x .6" x 2.6"
I have had this circuit in my
bass since the mid-eighties and it is different from most others in
that the shelves are wider and the slopes flatter. I like it because
it really does something without messing up the volume balance
between the strings, when you boost the bass you're boosting
everything between 20Hz and 300Hz instead of say 40Hz to 60Hz as in
many circuits. If I need to fine-tune my sound I'd rather do it on my
amp anyway. Hand soldered with high grade, discrete, components using
only 2 transistors so noise should be minimal though I have
experienced some RF interference. The circuit can be powered with 9V
to 48V, I use 18V.
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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. |
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This feature article is © 2001 by David King
Reprinted by the BGRA with permission
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