Project: Bass Preamp

[vipersassasin09]

hi, i was just wondering if there is a way to make a 3-band 27V EQ for a bass... for the bass i want a sweep between 20hz and 150hz... mid sweep of 250hz-1khz... and treble sweep of 2khz-3khz... and then of course have each with a +18db of power... when at zero though, it doesn't take any sound away, and it doesn't boost either... anyway... i wanna make a bass system that has volume for each pickup, a volume with treeble bleed on it, and a volume with black ice circuitry on it... then the tone is post EQ there will also be an active passive switch in the bass... so, there will be 5 stacked pots, and a on/off switch... along with 3-9-volt batteries... i am looking for someone who might be able to help me out... thanks...

[Albert Kreuzer]

Hi,

you might want to search for "state variable filter" and look up R.G.'s excellent article on parametric EQs at www.geofex.com.

My personal point of view:
I am a bassist and have done my share in developing preamps (www.albertkreuzer.com). Why would anybody want so many knobs on a bass? I mean, how professional does it look if you're on stage and have to stare down at your bass half of the time figuring out which knob does what?
(But I can see the necessity on Bootsy's bass with 5 pickups )

Just my $ .02

Cheers,
Albert

[Steve Conner]

The state-variable parametric EQ circuits are great. I've built several, and they work fine. The only drawback is that the frequency sweep control needs to be a dual-gang reverse log pot. They're hard enough to get on their own, and I imagine even harder to get as part of a concentric stacked pot with something else.

There is a simpler version which is basically the graphic EQ gyrator circuit, but the frequency pot varies one of the resistors in the gyrator. This only needs a single gang pot. The drawback is that the Q changes as you sweep the frequency. However for a small sweep range, this shouldn't be a problem. The state-variable circuits will do 10:1 sweep range easily, though, with constant Q.

Also, 18V is a convenient voltage because you can take a ground between the two 9V batteries and get +/-9V. Doesn't work with an odd number of batteries.

Albert: Active EQ on basses never did much for me either. The raw tone of bass pickups always needs a bass and treble boost, but the FMV tone stack in a tube amp does that naturally. But some bassists like to have a flat amp and get all the tone coming from their bass, and in that case it makes sense to have lots of knobs. (But why build it all into the bass? Surely it would make more sense to put the circuitry in a stomp box so you could use it with any bass...)

A parametric midrange control is nice on the amp though, to get that Jaco sound. I've seen Warwick basses with an onboard bass boost that could shatter your speakers completely, but I'm not sure how useful that is musically, unless you were doing the Jurassic Park soundtrack.

Oh PS, Bootsy doesn't need to think about what knob does what, they're all "Funk".

[vipersassasin09]

okay... i can see what you mean about the sweeps... i have thought about having the bass fixed at 50hz, the midrange sweep at 250-1khz... and the treble fixed at 5Khz... or 2.5Khz... which ever would work better... anyway, yah... and, what about phantom power? could you incorporate that into the circuit?

[Albert Kreuzer]

and, what about phantom power? could you incorporate that into the circuit?

Yes, of course. Best done with a transformer balanced XLR output. Look at early Alembics (no xfmr there though).
The downside is, you need an amp with phantom power or an external power supply (one more box and one more cable to carry). Been there, done that.

Oh, and while you're at it: What about MIDI? GPS? A coffee machine?
Sorry, couldn't resist

Cheers,
Albert


Steve: You're right about the funk

YouTube - BOOTSY'S BASIC FUNK FORMULA

[vipersassasin09]

what is a good site to get a schematic of a 3-band EQ like this though?

[Albert Kreuzer]

Simple, Easy Parametric and Graphic EQ's, Plus Peaks and Notches

[vipersassasin09]

okay... well, that tells me a little bit, i guess i am wanting a Board diagram, the layout you know... where are a few places to get those?

[Steve Conner]

There's not going to be a layout for a circuit board with the exact combination of features you wanted. You'll have to design it yourself... good luck!

[Bill Moore]

Years ago I got a parametric EQ kit from PAIA in OK. It has 4 bands, with 1/4 in and out jacks for each channel. I jumpered them all internally, and used the unit for monitor feedback control. Don't know if they're still availlable.