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Blend knob vs. Two volumes for signal loss

Discussion in 'Pickups & Electronics [BG]' started by Groovecenter, Aug 10, 2003.


  1. I have an aguilar OBP-3 with dimarzio ultra jazz 5's. There is a slight loss of signal while blending pickups, pretty much at anywhere except full neck and full bridge. The signal gets quieter as your blend into both equally mixed.

    I was told this was normal with any pre-amp lacking an active blend. I wanted to know If I replaced the blend knob with two volumes, if that signal loss would dissapear. My jazz has two volumes and there is no loss of signal with both pickups full on

    To reiterate, the signal loss is not huge, but noticable. If I replace the blend and volume config with individual volumes, will there be no signal loss? Thanks for the replies.
     
  2. yes- I think you will get less signal loss with 2 volumes.

    I recently changed my Yamaha RBX270F from vol-pan-tone to 2 DPDT switches (full-on bypass/off/sweet spot using 500k preset) + tone, and I'm much happier about the sound.


    with the original panpot, the centre position was pretty bland and nondescript- the flaw of the panpot is that in the centre pos neither pickup is at full volume.
    maybe if you had a custom-designed pot so in the centre position both were full-on it would work better.
     
  3. thanks for the reply, I actually already did it with two 250 k volume pots (cheap ones). As soon as I can Im going to order some that feel a little better and have a slower gradient. These ones drop the volume of the pickups pretty quickly. The signal loss is gone though, and the sound is good, but I think the new pots will be 500 k. (the pickups work with either)
     
  4. DeeZee

    DeeZee

    Oct 13, 2002
    Virginia
    I know this thread is a little old by now but just wanted to say that the 2 volume change helped my OBP-3 tremendously. I originaly wired it up with volume and blend pot and noticed the substantial volume loss when the pickups were blended anywhere other than full neck or full bridge pickup positions. I rewired the preamp using 2 volume pots and now I can blend pickups or pan completely to bridge or neck pickups and keep the overall volume the same. I will never go back to a blend pot setup now unless its an active blend which I hear counteracts this volume problem.
     
  5. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    The volume loss is from the blending of the two signals in parallel. A good pan pot is at full for both pups in the middle. Using a single blend pot or seperate volumes should not change anything unless the pots have different values. The volume loss with both pups on full is a well known problem from back in the days when all jazz basses came with 2 volumes.

    So at least on paper is shouldn't matter ;)
     
  6. DeeZee

    DeeZee

    Oct 13, 2002
    Virginia
    It could be some differences in pot values, don't know, but again I will say that there was a hugh difference between using the blend pot verses the 2 tone knobs. The aguilar instructions said to use the volume and blend pots that the pickup manufacturer recommends and that is what i did. The sound I was getting with the blend pickup in the middle (both pickups on "full") was like what I get with my current 2 volume configuration with both volumes only at 50 percent. It almost sounds like I had something wired improperly with the blend pot configuration but the aguilar obp-3 wiring diagram is not a complicated one really, its very clear where everything goes and I double and triple checked all the wiring just to make sure. Apparently the differences between what thoretically should happen and what really does, will vary from bass to bass.
     
  7. With a blend pot isn't it impossible to have both pups at full volume at the centre detent? Maybe not impossible but I can't really think of how it'd work, just because of the way that a potentiometer works. Active blends are different.

    On my Yamaha BBG-5A, I have a rather disapointing tone from the centre detent of my pan knob, at either extremity the tone is brighter and has more pahzaz but the centre is lacks a fair bit of that. Now I was thinking, just now, that thats due to one, maybe two, or all of three things: 1. The fact that as you turn a volume knob down, you can lose treble frequencies because they leak through the wiper of the pot to go to ground. So at the centre detent I've lost enough of the treble from both pups to sound crap. 2. The parrallel thingy that Moo said, which I don't understand. 3. The pots could be better matched to the tone I want to get out of the bass, ie 250k where I want 500k.

    I'm about to have a mate of mine's dad teach me how to solder properly (he used to be a technician with the air force, so he knows his stuff, at least thats what I hope), so pretty soon I'll be buggering around with just about anything I can get the iron to. Thinking a swap from the vol/pan to vol/vol, maybe with a push/pull series/parrallel switch if I can fit it in, have you seen inside the cavity of a Yamaha, they know how to do compact.

    Josh D
     
  8. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    Not at all, if the pots are the right value and kind you have the same thing you do with two volumes. Look at it this way, how does a single pot give full volume? By having two contacts connect. How does it add resitence? By placing a length of semi resistent material between the 2 contacts, varying the length of that gives you more resistence and less volume..

    Now simply make a pot where the contact at the full through side covers half of the pots sweep.

    You don't use the same kind of pots and if you simply use stacked pots you're screwed ;)

    All active blends I have seen use the same kind of blend pot as a passive blend control just with a different value. Also if you replace 2 500k volumes with a 250k blend pot you will notice a difference but that's not the blends fault.
     
  9. Thats what I was thinking would need to happen but is that actually used on most basses? For example with the OBP-3 I'm pretty darn sure mine just has a dual audio regular stacked pot with it (I'm yet to install it...). So if it doesn't have one would a cheaper electronics arrangement be inclined to have one?

    Josh D
     
  10. velocraig

    velocraig

    Nov 1, 2003
    NE Georgia
    Anyone have a link to a good schematic for this mod (2 vol rather than 1 blend)?
     
  11. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    I've never seen a pre amp use just a stacked pot for a volume blend. A simple way to tell is when you hook it up only connect one pickup. Listen for a volume drop between full on and the midpoint. If you hear a drop (and a drop on a normal volume pot from full on to halway is not tiny but most of your volume) you have the wrong kind of pots. If you don't hear a drop but hear one when you install the second pickup then the entire volume drop is the result of wiring 2 pups in parallel, a well known phenomena.

    You can also hook up the pot to a multi meter if you have one and measure the exact difference (if any) between full on and mid point.