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Building an active on-board Pre-amp

Discussion in 'Pickups & Electronics [BG]' started by Ferniff, Mar 14, 2016.


  1. Hello, I'd like to get some help on this project as I don't know where to begin. I know the basics of electronics where I can (with help from friends) read and wire up something from a schematic. But I wouldn't know how to get or understand the values of resistors/capacitors to get what I want. Anyways I have the Aguilar OBP-3 active pre-amp but I'm looking to create one from scratch for more versatility. What I'm looking for is a usual 3 band EQ with boost/cut on the Bass/Mid/Treble but in addition also be able to control what specific frequency will get the boost/cut. This will be also be wired up to a dual pot. I've found some EQ pedal schematics online but either it wasn't much help or just over my head. Any help at all would be appreciated.
     
  2. I've never seen a three band sweep (semi-parametric) eq circuit as a standalone bass preamp kicking around the net. but there's countless circuits around that will get you started on your own design. realistically you'll need to learn to use a spice program of some sort. and you also need a breadboard and some basic test equipment etc. a good understanding of maths and basic electronics principals wouldn't hurt either.

    one thing I will say is that commercial sweep eq preamps you see with stacked controls don't use standard, commonly available pots. so that may be a problem for a diy project.
     
    Rob22315 likes this.
  3. [QUOTE="RobbieK, post: .

    one thing I will say is that commercial sweep eq preamps you see with stacked controls don't use standard, commonly available pots. so that may be a problem for a diy project.[/QUOTE]

    I've seen a pedal schem. that was good for the mid range, but Ill need to find one for bass and treble and figure out how to combine them and make it onboard as opposed to a pedal. The pot would be challenging as well. I'll need something thats linear (for the frequencies) and dual so I can go from -10 0 10+ on the boost/cut.
     
  4. cfsporn

    cfsporn

    Aug 20, 2011
    New York City
    I know that @Passinwind has made his own onboard preamp in addition to his many not-so-onboard preamps. He may be able to help.
     
  5. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    I'd start by spec'ing maximum acceptable overall size, current draw, number of holes in the bass, and cost. Once those are known you can start chipping away at what can be done with over the counter pots, which are very likely to be the most limiting factor, especially if stacked pots are in the plan. My personal solution in my own builds has been to use switches rather than dual pots for defining frequency corners/centers. That tends to make for a lower distortion, more precise solution to boot, IME.
     
    cfsporn likes this.

  6. Size isn't a factor and I'm one of the few that like the "million button" basses. I'm working with a semi hollow Guild Starfire; it's a tribute bass to Phil Lesh's godfather bass but I voted not to stuff an alembic superfilter 2 into it. I'd much rather go with dials over switches/buttons.

    http://alembic.com/club/messages/411/209081.jpg

    This is my bass currently: https://i.imgur.com/vz5FOAC.jpg
     
  7. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    I'm very familiar with Phil and Jack's ancient basses, having seen them in action first hand many times. So, cool, what's your budget? Are you OK with doing an outboard power supply the way some Alembics do?
     
  8. I envy you for that. I was born way too late.

    Probably not, but what exactly would that entail? I'd really prefer to keep it to just 9 volt batteries inside. I should also mention, to add to the insanity to this, the neck and bridge will have their own pre-amp. I'm also looking to have a high-pass filter in there, because why not.
     
  9. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Start here: Can someone please tell me about old alembics?

    So for starters you just need to realize that the first tradeoff for all of that circuitry is hugely shortened battery life compared to something like your Aguilar preamp.
     
  10. Hmm interesting, I think I'd rather stick with the batteries and have a spot for easy replacement in the back of the bass. With pedals and possibly putting in a quad pickup, I'd rather have less wires coming out of the bass.
     
  11. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Phil and Jack both used umbilical cables, just sayin'. I don't do many battery powered circuits, so I probably won't have much more to add here in terms of specifics.

    You're taking on a huge project here, something I looked at trying many years ago myself when I briefly owned a Starfire, way before I had the tech chops to actually be able to do it. I'd recommend breaking it into small chunks, starting with building something very basic like the ubiquitous MusicMan 2-band knockoffs you can buy boards for on TB. Baby steps, in other words. Best of luck, and have fun with the journey. [​IMG]
     
    cfsporn likes this.
  12. Alright well thanks anyways! Between work and school I wouldn't have much time to work on this so I'll have put some time aside and learn more about what I'm doing and break the project into smaller parts.
     
  13. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    cfsporn likes this.
  14. +1 for Rod Elliott's excellent site.

    here's one of his projects that could easily be adapted for your purposes.

    this topology is very common for sweep eqs.

    I wouldn't worry about external power. a pre like this could work with just two dual opamps and a bipolar transistor for the input buffer. with the right opamps, you could get excellent battery life and noise performance.
     
    Passinwind likes this.

  15. Very nice! This is a big step in the right direction, thank you!

    I'm not quite sure what he means by "shelving". Is that a A or B switch as opposed to a sweep able dial?
     
  16. shelving in this case refers to the response of the bass filter. it's still sweepable.
     
  17. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    More exposition here: Equalisers
     
  18. Hey Charlie, good link!
     
  19. Awesome Sauce

    Awesome Sauce Already tired tomorrow

    Dec 21, 2011
    NW Chicago 'burbs
  20. Neat, exactly what I'm looking for. After spending a good dime on the Aguilar pre amps I think I'd rather build this myself, or at least try. It's good to know this does exist and what frequencis are used.
     

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