Dismiss Notice

Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

New volume pots have limited function... strange.

Discussion in 'Pickups & Electronics [BG]' started by Bassist4Life, Oct 10, 2005.


  1. Bassist4Life

    Bassist4Life

    Dec 17, 2004
    Buffalo, NY
    I have one volume for my P-pup and one volume for my J-pup. I have one tone knob. The electronics are passive.

    Background:
    This an old beater bass I have from back in the day. It's an Aria Pro II. It looks like it has been through a war. It still plays and sounds pretty good. I decided to use it as a project bass.

    It used to have an active EQ (w/passive pups). I decided to remove all of the active components and go strictly passive. I got 2 new 500k volume pots and I used the old 500k tone pot. I am new to wiring, so I decided to keep things really simple.

    Everything works; however, the volume pots don't really kick in until I turn them up about 80%.

    Also, when I turn the volume knobs all the way down, a little volume still comes through. Is this normal?

    Any thoughts? What did I mess up this time? :D

    Joe
     
  2. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    Sounds like you bought linear taper pots for your volume controls. Get some audio taper and you'll get a more useful range out of them.

    As to the volume not dropping completely, I'd have to see how you have them wired.
     
  3. yup what he said.

    Remember how we're always saying doubling watts only adds 3dB? So going up in 3dB increments labelled 1-10 you'd see 1w 2w 4w 8w 16w 32w 64w 128w 256w 512w .

    The volume control has to reflect that to make the volume seem to go up smoothly as the knob is turned. Instead of going up linearly (1/4=25% of incoming signal, 1/2 way = 50%), it increases volume in a logarithmic manner, sort of like the wattage curve above.

    Randy
     
  4. Bassist4Life

    Bassist4Life

    Dec 17, 2004
    Buffalo, NY
    Thanks! I was not aware of linear taper vs. audio taper. Shows how much I know.

    I called GC and said that I wanted to replace some volume pots. They asked, "How many k?". I said, "500k.". They said, "Yup, we've got 'em for 4 bucks each.". Now they're in my bass.

    Should this guy have asked me if I wanted linear or audio?

    Joe
     
  5. He's either got no idea what he's doing, or grabbed the wrong ones by mistake. Its common knowlege you need audio taper for volume pots. Among electronics guys, maybe not the gen public...

    Randy
     
  6. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    Nowadays it seems the common theory is changing the value of pots is done for tone reasons :eyebrow: In the old days it was to even out the response curve of the pot.

    For example, if your bass' pickups can be silenced with 200k of resistance and you use a 250k pot they won't sound off until you twist the knob most of the way, maybe around 1 or 2 out of 10 on the knob. If you switch to a 500k pot you may now turn them off around 5 or 6 on the knob leaving half of the knobs sweep giving you different degrees of off. Switch to a 50k and you'll never get your bass to turn off.

    So I'm guessing if you changed to 250k pots you would find more of the knobs sweep to be usable.
     
  7. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    THis actually wouldn't work that way. Rember, when you turn down a pot, you are decreasing resistance between the ground and the pickup output. So any one of those pots will work, but the 50K's may let more bleed to ground on full on than would the 250K's or the 500K's. This is also partially why tone is so affected by pot changes.
     
  8. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    So you're saying a 250k will let your bass be louder than a 50K?
     
  9. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    This i probably entirely dependent on the pickups themselves, as EMGs are louder with 50K's. I think it all depends on the pickup's internal impedance as well. Impedance matching can play a big role in this.
     
  10. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    That doesn't really jibe with the earlier statement. ;) And you also jumped to active pickups.

    Would EMG's be louder with 250k's? You're saying they are louder with 50k's, is that loudest? Louder than what?

    How do you impedance match a pot?
     
  11. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    Well, in this particular circumstance, I figured it was needed to pint out the difference there. I tried my P with 250k pots, and didn't like how i acted. The volume was jumpy and unpredictable. It would increase or decrease very quickly with a 250. But with an active pickup, it has a low impedance output anyways, so you generally want to match that. With passive pickups though, lower output pickups generally tend to like 250's on volume. Higher output work better with 500's, generally speaking. With tone controls though, pot value can make a huge difference. A 1 Megohm pot with give you a nice bright sound, as it bleeds less treble to ground than would 250 or 500.
     
  12. Moo

    Moo Banned

    Dec 14, 2002
    Oakland, CA
    I don't think that deals with any of my questions ;)

    Are you saying changing a pots value will change the bass' ultimate volume?

    A 250k pot is jumpy and unpredictable? Are you attributing this to the value being 250k?
     
  13. Bassist4Life

    Bassist4Life

    Dec 17, 2004
    Buffalo, NY
    When I changed the pots, I wasn't considering what it would do to the tone. The original set up had one volume for both pups. Pup selection was done with a 3-way toggle. I switched over to one volume for each pup. I bought two new volume pots and removed the original volume pot. I could have left it in there, but I figured that I'd start with fresh matching parts.

    The reason I picked the 500k is because that's what the old pots were. I figured that I couldn't go wrong if I matched them up. I never considered "linear" vs. "audio" pots. I'm looking at the package the new pots came in.

    The part number and description is:
    GC702 CTRL POT D500K DIME SIZE

    There is no mention of linear or audio. :meh:

    Joe
     
  14. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Memphis
    Moo's notion is very faulty. In practice, you won't hear much of a difference in the sweep of a 250K and a 500K pot. The 500K pot will sound a little brighter when on 10.

    The taper of the pot (audio [logarhythmic] or linear) is crucial.
     
  15. Yeah, you guys are way off. The volume pot shows the pickup its full resistance. If you have a high impedance pickup, you want a higher value pot to keep from loading it excessively. Medium to slight tone change could result. The impedance of whatever the pot drives is in parallel with that, to whatever degree the pot is turned up. Volume = off, the pickup sees the pot resistance only. Volume=full, the pickup sees the pot impedance in parallel with whatever the pots driving. As the volume goes down, the impedance the pot is driving is gradually isolated from the pickups.

    But the sweep part of the pot goes from 100% to 0%. Period. None of this nonsense that a 250k pot can't turn all the way off for some impedances of pickups.

    The pot forms a voltage divider. When the slider has equal resistance on either side, you get 50% of the voltage going out that's coming in. On a linear pot, that's where the knob is at the halfway point. On an audio pot that point is way down on one end of the pots range of motion. When the pot is all the way up, the same voltage going out is what went in. When the pot is all the way down, the slider is shorted to ground, no signal from the pickup goes through.

    Any other behavior indicates bad pot, or incorrect wiring for a volume pot.


    Randy
     
  16. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL

    Right you are. I was trying to illustrate a little more of the technical side. But I guess I wasn't really typing as clearly as I thought. Oh well.

    Moo, what I was meaning was that MY bass with EMG's didn't work that well with 250's. EMG's circutry is designed to work with the 50K pots. That has to do with their output impedance. Like steveksux said, you don't want to load the pickups excessively, or they won't sound right.

    To clarify here, I think what moo was thinking of is that the pot turns down the volume by pure resistance. But when the pot is on 0, it is pouring the whole output of the pickup into ground. On the other side, it is putting it through to the amp. There is a resistance between the pickup and ground now equal to the value of the pot. And remember also, that the proper function of a pot is dependent on the wiring around it.
     
  17. Should cross post this to amps, too, cause that's exactly how the volume control on a power amp works. All it does is reduce the sensitivity of the power amp. Not the output power. Power amp at 50% can still put out full power, it just requires you to turn up the preamp, or the volume on your bass to get a hotter signal to the power amp.

    Randy
     
  18. Bassist4Life

    Bassist4Life

    Dec 17, 2004
    Buffalo, NY
    I spoke with a guitar tech at a local guitar store. He told me that I may have bent the connectors on the pot by tightening it down too much. I checked to see if this was the problem, but no cigar.

    Plan B: I did a little web research and found the following; perhaps you guys can confirm this for me:

    A500k = "audio"
    B500k = "linear"
    D500k = ?

    My bass has brand new D500k volume pots.
    My bass used to have one B500k volume pot when it was active.

    The guy at GC never told me that there are different kinds of volume pots. Do you think I should switch to B500k or look for A500k?

    Thanks,
    Joe
     
  19. Get the A pot, audio taper.

    Randy
     
  20. Dan1099

    Dan1099 Dumbing My Process Down

    Aug 7, 2004
    Michigan
    Tone pots are linear, correct?