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Blend knob mod for passive jazz

Discussion in 'Pickups & Electronics [BG]' started by Cristo, Jun 6, 2006.


  1. Who here has replaced the V-V-T config on a passive jazz with a V-B-T and deemed it a worthy mod?

    I like the idea of one knob for volume and one for fine blending, but I'm hesitant to go through the trouble to discover that either it sucks or it's not much of a difference.

    Also, I've read that some people experience a volume drop at the center position - although I notice a volume drop now when both Vs are on full anyway.
     
  2. I can't see a down-side. I find it clumsy to have to use 2 knobs to effectively blend the pups. I have never modded an instrument before. Would this mod be hard to do?
     
  3. Philbiker

    Philbiker Pat's the best!

    Dec 28, 2000
    Northern Virginia, USA
    I've never done this mod, but I've converted a V-B-T to V-V-T with spectacular results. I greatly prefer V-V-T to V-B-T personally. I'm sure it would work fine for you.
     
  4. TL5

    TL5

    Jun 27, 2005
    Nashville
    Although it's not a J, and it has active EQ, I modded my fretless from VV(EQ), to VB(EQ). To match my five-string.

    My reason was, when I play it at church I wanted to be able to kill the volume w/o losing the subtle blend between the pups. At church there's not an opportunity to 'test/noodle' to adjust the sound back after killing both v's.
    So the mod made sense.

    Since then, I've added a volume pedal to my pedal board. I've considered returning to the VV(EQ) set up because the variations are better with two volumes.
    IMHO, YMMV, a different bass could react differently.
     
  5. pj-mike

    pj-mike

    Nov 22, 2005
    Bridgewater, MA
    I did this mod when I added the bridge pickup. For the style of music I'm playing, It was not all that useful. It's bennefit would be if you had to change from mostly neck pickup to mostly bridge. I my case, I never use more bridge then neck pickup. I think that kits for this setup are available through most parts dealers, If you decide to go that route.
     
  6. guitar-mod.com

    guitar-mod.com

    May 4, 2006
    This is one of my favorite mods for a j-bass.

    Here is a diagram I drew up if you haven't found a diagram already.

    Cheers,

    Andy

    jbass_mod.gif
     
  7. Eggman

    Eggman Supporting Member

    Dec 3, 2004
    Denver, Colorado
    I found a set-up like this on ebay. Also had a series/parallel switch. Frank - the guy who made it has a website - www.amazing-bass.com.

    Easy to install - but probably more expensive than if you did it yourself.

    Added these to a 4 and 5 Lakland Skyline JO - they sound great.
     
  8. HeavyDuty

    HeavyDuty Supporting Curmudgeon Staff Member Gold Supporting Member

    Jun 26, 2000
    Suburban Chicago, IL
    Moved to Pickups...
     
  9. If you don't feel confident enough to do the project yourself, look into some prewired harnesses. Go here and look at the JB1 Blender harness. Stan will go ahead and wire that up for you, and all you have to do it put it in place on your control plate and wire it to your pickups.
     
  10. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Pasco, WA
    Right on!

    Thanks man! This is going ointo my archive!

    :D

    Joe.

    EDIT:Er...what about values?
     
  11. I was in a guitar store one day playing around with a cool bass that had a magnetic pickup and a Piezo bridge. It also had a blend pot that allowed you to control the mix ratio of Piezo to magnet. It was a neat idea that worked well. So when I decided that I would add magnetic pickups to one of my guitars I thought what better way to mix them with the Mike Christian Piezo Bridge than with a blend pot? After hearing other builders sing the praises of the Blend Pot offered by instrument supplying Gods Stewart MacDonald I decided to give it a shot.

    Blend Pot Closeup A quick trip to Stewart Mac turned up exactly what I was looking for. My order arrived 3 days later as usual. The pot is small which makes it easy to fit into your guitar but tricky to wire. Using the instructions on the Stew-Mac web site, I didn't have any trouble wiring it up to my two S-90 pickups but a novice might find it tricky because of the close quarters of the soldering lugs.

    Once the pot was installed I tweaked it a little bit and loved the smooth action and the center detent. That's about where the love affair ended. As I rotated the knob from "Full Bridge" to "Center" to "Full Neck" I noticed three distinct sounds, bridge, center and neck. No interesting, subtle "in between " sounds were apparent to my ear. This passive blend device does nothing more than a 3-position switch would do. I'm sure there are interesting possibilities for this little trick if one were building a 2-channel pre amp or something like that. However, right out of the box it's is completely underwhelming and not worth the time or effort to install.
     
  12. That's interesting, and strange, because I was expecting a "blend" - a continuum of tones between the pickups, and not just one, the other, or both. Probably exactly what you were expecting!

    Anyone else have that experience?

    I just find the two volumes a little unwieldy, and only the first 10% or so of travel has any impact on the tone as far as I can tell.
     
  13. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Pasco, WA
    It sounds like maybe the wrong value of pot or taper was used. IME blend knobs kick separate volume knobs butts!

    Or maybe too much ear wax?

    :bag:

    :D

    Joe.
     
  14. bmc

    bmc

    Nov 15, 2003
    Switzerland
    Vol - Blend - tone

    1. Set the volume once
    2. Work the blend to quickly nail the bass/mid sound you want for the song

    If there is volume loss, which I have never noticed, what's the big deal? Set the volume to what's required.
     
  15. davpal

    davpal

    May 19, 2006
    Lambertville, NJ
    I'm curious about why the pot is not blending - what value did you use - 250k or 500k? What value pot for the master volume? There is another way to wire up a blend pot that can be found on GuitarElectronics.com that doesn't ground the pickups but shunts the signal (+) of the pickup back to the neg. wire (shield) of that pup. I'm about to install a blend pot in my Yamaha fretless (now 2 pup,v-v-t) and not sure what path I want to take. I guess I may have to experiment and find out.
     
  16. StuartV

    StuartV Finally figuring out what I really like Supporting Member

    Jul 27, 2006
    Manassas, VA
    I know this is an old thread, but I'm having exactly the same problem that Searcy described. I got a pre-wired control plate with a blend knob for my passive Jazz.

    If I turn the blend knob from 5:00 (neck soloed) to 12:00 (both on full) to 7:00 (bridge soloed), it only really seems to do anything between about the 11:00 to 1:00 positions.

    From 1:00 to 5:00, I seem to have a nice full neck sound. From 11:00 to 7:00, I have a nice full bridge sound. At 12:00, I have noticeably less volume and a really thin sound. The tone seems to change very smoothly but very rapidly as the knob goes from 11:00 to 1:00.

    The pickups are SD SJB-1's if that info helps.

    The control plate was pre-wired so I just had to solder the pickup hot leads (one white, one yellow) to the lugs on the blend pot, the pickup grounds (black) and the bridge ground wire I attached all to the ground lug on the output jack.

    Can anybody shed some light on what is wrong?

    Is there any specific test I can do to figure this out? It seems like maybe the problem is the blend knob taper is simply bad for use in this application and the resistance increases way too quickly or something.
     
  17. StuartV

    StuartV Finally figuring out what I really like Supporting Member

    Jul 27, 2006
    Manassas, VA
    I just found this in a Blend Knob review on StewMac.com. Might this be my problem?

     
  18. fenderphil

    fenderphil

    Sep 1, 2006
    Houston, TX
    reverse the leads on one of the pickups.

    its a phasing issue when both are blended together.

    its probably bad advice, but try it and see, lol
     
  19. StuartV

    StuartV Finally figuring out what I really like Supporting Member

    Jul 27, 2006
    Manassas, VA
    Well, that was actually my first thought. But, if phase were the problem, wouldn't my 60Hz hum increase when the knob is centered? Instead of going away?
     
  20. Sparkdog

    Sparkdog Supporting Member

    Sep 18, 2006
    Burbank, CA
    I wouldn't go so far as to say a Jazz with 2 volumes is unusable for me, but it sure isn't user friendly. I have 2 Jazzes that I gig frequently and both have the VBT setup, along with hum canceling pickups.

    That combination gives me all the tonal variety we love in a Jazz, but I can also fade in and out of tunes, turn the bass off between songs without messing with my blend, and easily adjust my level mid-song.

    I do hear a VERY slight drop in volume with both pickups on full, but the same is true with every VVT bass I've tried. I almost never run the bass that way anyhow so it's a non-issue.

    For anyone keeping score my pickups are DiMarzio Ultra-Jazz and DiMarzio Area J's, both with 500K pots so I get all the highs the pickups are capable of.
     

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