Ultimate No-load Ungrounded Blend Pot (Pics!)

Discussion in 'Pickups & Electronics [BG]' started by walterw, Aug 13, 2014.


  1. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    what kind of bass is it? american standards already have shielding, that's what the wired screw going into the wood is for.

    otherwise, here's what you want:
    419pBD3FQ0L._SY445_.jpg
    dries almost instantly and is nearly as conductive as copper foil. it'll take you ten or 15 minutes to remove all the guts and masking tape up the edges of the holes, then 30 seconds to go outside and spray a coat into the cavities.

    remember that for this stuff to work it needs to be grounded, so you'll need to put a little wood screw into the bottom of each pickup cavity, attach a wire to it and solder that wire to ground. for the control cavity just arrange the masking tape so that the shielding paint comes up and over the edge enough to contact the control plate, ideally right under a screw.
     
    Last edited: Nov 1, 2016
    Torrente Cro likes this.
  2. 4StringTheorist

    4StringTheorist Supporting Member

    I've got a set of MN250K pots in from Amazon now, so going to be trying this for my active 5 and VBTT passive 4, most likely later in the coming week.
     
  3. vin97

    vin97

    Mar 7, 2016
    Germany
    Cool thanks, so less work than I expected. How thick do I need to spray it, in other words will it be obvious when I've sprayed enough?
    Regarding the grounding, can I solder a wire directly to the coating or avoid drilling into the body in another way (like using aluminium tape)?

    I have a japanese standard jazz.

    Have there been direct comparisons of copper foil vs conductive paint shielding?

    @4StringTheorist: VBTT, meaning volume-blend-tone-tone?
     
    Last edited: May 16, 2016
  4. 4StringTheorist

    4StringTheorist Supporting Member

    Yes indeed. A slightly different capacitor on each tone pot. I'm going to isolate each pickup with its own 15KOhm resistor so the tone knobs interact less. The MN blend pot will just be icing on the cake!
     
  5. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    yep, when it's opaque grey you're done.
    you can't solder right to the coating itself; you'll typically just drive a short little wood screw right into the wood (no drilling necessary).
    measured it plenty of times now with my meter; the graphite brush-on paint might read like 1200Ω DC resistance from one end of a cavity to the other (after taking forever to dry and smudging everywhere), while properly done copper will read close to 0Ω.

    the nickel spray after one shot might read 20 or 30Ω from one end to the other (way more than good enough) and if you bother with a second solid coat, it could get down to 3 or 4Ω.
     
    Last edited: Jun 5, 2016
  6. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    now to be clear, all this shielding will have no effect on single coil hum!

    all it does is reduce or eliminate that extra buzz you hear when you take your hands off the strings.
     
  7. vin97

    vin97

    Mar 7, 2016
    Germany
    ohhh, I misunderstood it then.

    well, i guess no shielding for my fender :D

    thanks for the help anyways!


    Totally unrelated but I have been thinking about a "variable jawari bridge", kind of like this fretless bridge but with metal jawari "ramps" instead of wood ones that can be rotated up and down.
    Now the question is how do I actually start developing such a thing :D
    Maybe some 3D modelling programs you can suggest or somebody who has done something similar before?
     
  8. Hey @walterw, I got a question about blend pots, and I'm wondering if I can use one for a bit of a different purpose, and what you've shown in this thread to isolate them may just be what I'm looking for...

    I'm looking to possibly wire a two pickup bass into stereo (or dual channel) signals, so I can split the neck and bridge pickup into different signals and send them through their own external effects.

    This is like the Ric-O-Sound of a Rickenbacker 4001/3, however, instead of having a volume pot for each pickup, I'd like to have one blend pot (with a center detent) for both pickups, so that as I turn down one pickup/channel, I turn up the other, but without actually combining the signals.

    My understanding is that a Blend pot is essentially two stacked volume pots with reverse wipers, so I don't see what it wouldn't work, but I don't know enough about how they are built to know for sure.

    Do you know if I could use a blend pot to do this, and if so, would I have to do any mods to it?
     
    Last edited: Feb 1, 2017
  9. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    i think it would be doable.

    just use a regular M/N blend pot, but instead of the jumper between the two layers, each layer's out would go to a separate jack.

    you'd have to put the grounds back on the blend if you wanted to shut off one pickup or the other totally, which means you want a higher-value blend to prevent too much loss.

    the question then becomes having volume controls, they would need to be separate for each pickup as well.
     
    Last edited: Feb 1, 2017
    Matthew_84 likes this.
  10. Thanks Walter!

    I see Bourns has a 500k M/N blend pot. Would this work? I'd like as little loss as possible.

    Also, regarding the ground, I just realized, where the heck would I send it? Lol! I was just thinking of using a single stereo (TRS) jack, but when I use a splitter to split it into two separate mono cables, would I split the ground into each mono cable?

    And yeah, I realized I would lose the volume controls, but I actually think I'm okay with that.... I can adjust the levels with the different effects on each channel, and I'm going to be blending both channels back into one amp, so I can always turn down at the amp.
     
    Last edited: Feb 1, 2017
  11. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    yep.
    ground is ground, connect them all together. both pickup grounds would still go together, and could share a ground from a stereo jack.
     
    Matthew_84 likes this.
  12. Great! Thanks Walter!

    I appreciate your help.
     
  13. Hey @walterw,

    Sorry to bug you, but I was avoiding putting in a volume pot because I didn't want two volume knobs as well as the blend, but could I not also use a second blend (but without a center detent) and wire one channel to one outer wiper of one pot and then wire the other channel to the opposite outer wiper of the other pot to be a master volume for both channels, effectively turning down both channels independently, but at the same time.

    Would I have to cut the traces off of this master volume blend pot?

    And just to confirm, would I have to cut the traces off of the channel blend pot previously discussed?

    Thanks Walter
     
  14. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    you could to it not with another blend pot (the sweep would be all wrong) but with an actual ganged dual pot, where the two pots both turn off one shaft and are the same as each other.

    i gotta say though, there's a pretty good argument for skipping all this complexity and just using two volumes to do all of it.
     
    Matthew_84 and Passinwind like this.
  15. rufus.K

    rufus.K

    Oct 18, 2015
    SoCal
    What about stacked volume knobs
     
    Matthew_84 likes this.
  16. Thanks Walter! I've never heard of ganged dual (or stacked volume) pots. I'll look into those.

    I realize it would be much easier to just have one volume pot for each channel, but I like the idea of turning down one channel while turning up the other simultaneously and equally (assuming all of my levels are equal through the various effects).

    I don't really need the master volume knob and I may just skip it, but it would be nice to have, just in case.

    Quick question regarding the blend knob though, would I have to cut the traces off as you did in the OP to keep the chennels separate at all times?

    Thanks Walter
     
  17. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    not at all.
     
    Matthew_84 likes this.
  18. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    i think means you'll want an A/C blend rather than an M/N. the M/N has both pickups at full volume in the middle and just turns one or the other down, while the A/C doesn't let one side hit 100% until the other side is off.
     
    Matthew_84 likes this.
  19. Hmm, the A/C blend pot sounds right, but I guess when its at center, each pickup only puts out 50% (roughly) of its volume?
     
    4StringTheorist likes this.
  20. soundfan75

    soundfan75

    Dec 5, 2011
    Texas
    Hey @walterw, this goes way back to your layout diagram. Why the linear volume pot? Traditional tapers are audio in J basses right? Does this provide a better response to the control?
     
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