EB-0 wiring help

[Highlander]

Crikey - sounds like your haveing a real nightmare there... I still haven't figured out where mine's gone screwy... don't envy you one little bit...

[Pilgrim]

Some good news - the wiring change Dave suggested (swapping the input and output leads) fixed the volume control problem!  Now each pickup operates independently.

Dang, that mudbucker is HOT!!!!

Two things left to fix:

1) The pickups must be out of phase with each other; when I raise both volumes up full, the output gain is reduced and the sound is much less deep.

2) whenever the mudbucker is turned up and I don't touch the strings, I have slight hum.  When I touch the strings it dies out, but when I touch the metal mudbucker cover, I get a LOT of hum.  I conclude I need another ground wire from the 'bucker to the ground system.

Any comments on how to change the phase of one pickup?  I can easily reverse the input and output connections on one of the two (back to its original setting), if that will do it.

[exiledarchangel]

Yup, that would do the trick, just swap the hot and ground on one of the pickups. As for the grounding problem of the mudbucker, check with a multimeter if its ground is soldered ok on the chassis of the pickup or it has corroded or something.

[Psycho Bass Guy]

1) The pickups must be out of phase with each other; when I raise both volumes up full, the output gain is reduced and the sound is much less deep.

Try swapping the polarity first, but don't be surprised to find out that what you're hearing is phase cancellation from the distance the pickups are apart. I have a couple of Jazz basses that get quieter with both pickups on, and they're wired correctly. That is still phase cancellation, but it is due to the difference in phase caused by the difference in string motion and not electronic polarity.

2) whenever the mudbucker is turned up and I don't touch the strings, I have slight hum.  When I touch the strings it dies out, but when I touch the metal mudbucker cover, I get a LOT of hum.  I conclude I need another ground wire from the 'bucker to the ground system.

Are you using shielded wire or two separate leads? If you're using separates, I recommend changing out the mudbucker to shielded wire and tying the shield to its cover.

Any comments on how to change the phase of one pickup?  I can easily reverse the input and output connections on one of the two (back to its original setting), if that will do it.

Reversing the connections will change the polarity of the pickup, which will change the phase of its output AC, but be aware that polarity and phase are not the same things, though the terms are often used interchangably.

[Pilgrim]

Try swapping the polarity first, but don't be surprised to find out that what you're hearing is phase cancellation from the distance the pickups are apart. I have a couple of Jazz basses that get quieter with both pickups on, and they're wired correctly. That is still phase cancellation, but it is due to the difference in phase caused by the difference in string motion and not electronic polarity.

Are you using shielded wire or two separate leads? If you're using separates, I recommend changing out the mudbucker to shielded wire and tying the shield to its cover.

Reversing the connections will change the polarity of the pickup, which will change the phase of its output AC, but be aware that polarity and phase are not the same things, though the terms are often used interchangably.

I tried swapping polarity on the mudbucker but that just killed its gain - no sound.  I returned the leads to their functional settings.

The mudbucker's shield covers part of the wire length but doesn't run to the pot.  I soldered an extra ground wire onto the shield that did still exist and connected it to the cover - the pickup was well grounded to the same shield.  No joy, no change in hum.

You may very well be right that the pickups are canceling each other out of differences in string motion.  Something is certainly canceling out, and it's reducing both gain and bass sound.  When I have both pickups turned up, the sound is thin but if I turn the Model One down about 20% the gain jumps up and the sound gets fatter.

For the moment it's playable if I only use one pickup at a time.  The hum from the mudbucker isn't audible if I don't touch the cover by bracing my thumb against it. I'm at least be able to practice with it.  I'm not sure what the next step is, but if I can kill the hum from contacting the mudbucker, I'll be able to use one pickup at a time.

I'll say this - that Gibson pickup is HOT and LOUD.  It's amazingly powerful and wooly sounding!

[Dave W]

The mudbucker's shield covers part of the wire length but doesn't run to the pot.  I soldered an extra ground wire onto the shield that did still exist and connected it to the cover - the pickup was well grounded to the same shield.  No joy, no change in hum.

I suggest trying it straight to the jack to make sure it's not the pot.

You may very well be right that the pickups are canceling each other out of differences in string motion.  Something is certainly canceling out, and it's reducing both gain and bass sound.  When I have both pickups turned up, the sound is thin but if I turn the Model One down about 20% the gain jumps up and the sound gets fatter.

That sounds like the type of phase cancellation Psycho Bass Guy described (difference in string motion, not polarity). It's just the way these two pickups interact at those positions and distances apart.

[Psycho Bass Guy]

I suggest trying it straight to the jack to make sure it's not the pot.

Yeah. On a two-lead humbucker, there should be no difference in soloed output by changing polarity. The hum may be coming from the pot. 

[exiledarchangel]

You can try something else for the pickup cancellation, that trick some old Ricks have, solder a small capacitor (ricks have a 0.0047uF I think) in bridge pickup hot wire. That will choke bridge pickup's bass frequencies and they will not cancel the bass frequencies of the mudbucker when used together.

The disadvantage is that bridge pickup soloed would sound kinda tinny. You can read about that here:

http://www.joeysbassnotes.com/Rick%20maint.htm#cmod

[Pilgrim]

Hey Dave and PBG, sounds like a good idea to try going direct to the jack.  At least with the push-pull switches out of that bass, it's a LOT easier to mod the wiring.  The pots are CTS (supposed to be good ones), but that doesn't mean I haven't done something creative to induce hum.

ExA, I'll hold your idea as backup.

The whole string-cancellation thing is kind of a surprise to me, considering how many different wacky multi-pickup installs I've seen, none of which mentioned encountering that problem.  If it keeps up, I may find that it's a reason to yank that Model One and come up with a black PG square to cover the hole.  OTOH, there is a difference in the sound of the two pickups, so even if I can't use both at once, having the option of using one or the other does slightly increase the versatility of the bass.

So far, I'd say the differences in the pickups are:

1) The Gibson mudbucker is hotter, puts out more gain, and also is a wooly mammoth.  Definitely a vintage EB-0 wool/mud sound.  I dig it a lot.  Using this pickup, I don't think I'd need my overdrive pedal - it sounds overdriven in its natural state.

2) The Dimarzio is less hot and puts out 80-90% as much gain, and if the Gibby pickup is a wooly mammoth, the Dimarzio is a wooly buffalo.  It's not quite as rough and is slightly more clear, but definitely nothing like a modern-sounding pickup for clean sound.

[Pilgrim]

OK - with the pot for the Model One disconnected from the jack, the Gibson humbucker still hums like a wild beast.  Even with the pickup cover grounded to the pickup, I get hum when I touch the metal cover.

I guess the next step is to replace the pot with a different new 500K ohm pot that I have...and see what happens.

[Dave W]

The fact that you got no sound when you switched leads makes me think the problem isn't with the pickup. Can't say for sure, though. IIRC Bill had that mudbucker in a bass but after he sold it to me, I never did get around to my project.

[Psycho Bass Guy]

How good is your ground connection to the bridge?

[Pilgrim]

How good is your ground connection to the bridge?

Good question.  WHERE does the ground wire run in these darn EB-0 models?  I can't see anything running directly to the bridge.  There's a "mystery wire" coming out of the body next to the jack, but I haven't figured out where it goes.

When I got the bass there was a bit of what looked like solder-wick wire folded up at the bottom of the bridge post hole nearest to the pots, but it wasn't attached to anything.  I removed it so the post would screw in fully.

Maybe I'll just clip a jumper cable onto the shield side of the jack and run it to the bridge.  Hadn't thought of that before, but it would ground the bridge and strings for sure.

[exiledarchangel]

You must change the title of the topic to something like "The quest for the holy ground"!

[drbassman]

Usually, the mystery wire exits out of the top of the control cavity.  The other end is supposed to be wedged between the lower bridge insert and the body.  If it isn't making good contact, that might be your problem.  Run a temporary jumper from the jack to the bridge to see if that helps.