1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  

Filter preamp for single pickup

Discussion in 'Pickups & Electronics [BG]' started by matbard, Nov 24, 2018.


  1. matbard

    matbard

    Jan 27, 2006
    Florence
    Hi,

    Alembic wise, is there a "modern" filter preamp for a single pickup(P-style)? Maybe with a variable resonance mode.

    Thanks in advance,

    - Matteo
     
  2. A year or two ago there was a thread on this and 1 or 2 of us posted schematics. If you know someone who is into electronics, you could have it made.
     
  3. Jeff Scott

    Jeff Scott Rickenbacker guru.......... Supporting Member

    Apr 11, 2006
    Why not an Alembic preamp, just not with a pan control?
     
  4. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Yep. This project is one variation on the theme: The Passinwind Open Source Preamp

    But mine is a hybrid deal, not just a "filter" preamp.
     
    kesslari likes this.
  5. matbard

    matbard

    Jan 27, 2006
    Florence
    Hi,

    The commercial Alembic Activator for P-Bass has only two pots, one for volume and one for frequency control. You can add a 2 or 3 step variable "Q" switch, but not a continuous variable resonance control. Since I have a 3 knobs arrangement on my bass, I would like a Volume/Frequency/Resonance arrangement...
     
  6. kesslari

    kesslari Groovin' with the Big Dogs Staff Member Gold Supporting Member

    Dec 21, 2007
    Santa Cruz Mtns, California
    Lark in the Morning Instructional Videos; Audix Microphones
    @Passinwind 's preamp is pretty darn cool. Wish I had the build chops to try it.
    ACG EQ02 is a single filter, and works well on a single pickup bass. Great sounding preamp. I have the EQ01 (2 pickup) in my Zon
    Less pricey than the Alembic, as well.
     
  7. Jazz Ad

    Jazz Ad Mi la ré sol Supporting Member

    I know external devices thatcan accomplish this but I'm not aware of a readymade onboard bass preamp that would allow such settings.
    Active electronic control choices are rather shallow. Out of ACG and Alembic, everything you get is bass mid treble arrangements with sometimes small differences like at Artec or Audere.
     
  8. The schematic I posted sounds ideal. Although it only has 2 resonance settings. You could certainly expand that with a rotary switch of course. A resonance pot can be added to a sallen key lpf, but it's limited and you start looking at state variable filter topology instead.

    I've messed around with this in my P bass and tbh, it didn't really thrill me. But fwiw, I'd recommend wiring the pickup in parallel, then adding 5 or 6 dB of gain to the pre. This way you'll have a lot more treble to sweep through and tweak.
     
  9. matbard

    matbard

    Jan 27, 2006
    Florence
    Hi Robbie,

    I read your posts in the old filter thread and they are very instructive! If I'm not wrong, you suggested the SVF for low impedance, full range pickups(like Alembic or EMG) and the Sallen-Key type for conventional, hi-Z pickups, like the Dimarzio Model P I have. I could easily put a switch to change the configuration of the two half-bobbins thru series or parallel operation(that's a mod I wanted to add despite of the preamp!), but really I want to get rid of the stock B/T preamp and put a filter with resonance control, maybe with a passive/active switch. I think I will go thru a design of mine("With a Little Help From My Friends which have more expertise than me). I noticed that there are new opamps with very low noise and power consumption, like the OPA1692, ADA4084 or ADA 4807 that are interesting to mess with...
     
  10. SVF or sallen-key it doesn't matter really. Both will offer lpf with a freq and res adjustments. The sallen-key topology is just nice because it is a simple circuit with less parts. The reason I recommend low impedance/low inductance pickups is just that their resonance will be higher in freq so it just gives you more treble to play around with in the first place.

    When I had this thing in my P, I had a 4 pole switch for active-passive because it was also switching the pickup from parallel to series at the same time. The front end of the pre had 6dB of gain to boost the parallel setting to the same level as the passive (series) setting. At first I had a push-pull for two res settings, as in the schematic I posted. But later I redesigned the filter with a gain adjustment in the feedback loop. This controls the resonance. I even found a stacked pot with a single gang linear and a dual gang reverse audio. IOW three gangs. (They are usually used in mixing desks for parametric eq.) But I just didn't think it suited this bass. I must say though, that it is really cool playing around with resonant LPFs with stingray pickups...

    As for opamps, well you can trawl through lists and lists of them. I wouldn't get too caught up in it TBH. If you go for the sallen-key option, you are only using 2 opamps so current draw won't be crazy, and you'll probably have a fairly modest input resistor and only 6 dB of gain so it doesn't need to have insanely low noise. Plus of course, you are rolling off all the treble above your resonant freq.
     
    Last edited: Nov 26, 2018
  11. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    I'd like to invite you to post in my open source design thread that's linked up thread if you would be so kind. We can always use new input! Yel_wink.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.