The EB2 Triple Bypass (Choke Bypass Modification)

[chromium]

I looked inside my EB-3 last night, and that inductor only has two wires coming out of the tin - the black one is soldered to the outside of the tin as you mention.  In addition, there is a piece of hook-up wire soldered to the tin that grounds it to the rest of the circuit.  I tried to look inside my EB-2D, but couldn't get any sort of view to see the inductor outputs on that one. 

I'm wondering if your third wire is just a tap-point midway thru the inductor coil?  You might be able to tell which is the mid-point using a multimeter, and measuring the resistance between the black wire and each of the two colored wires - higher value being the full coil.  That won't tell you the value of the inductor, though.  You can get multimeters that measure capacitance/inductance.  Might be worth picking up a cheap one for this project, or taking the part to a local tech to measure for you.

Any thoughts from others on my assumption?? (eb2, Jake...)  Also, is the value of the inductor really supposed to be 15 Henry (as in the EB2 schematic above)?  For some reason, I thought the value they used was 1.5 Henry...  Just want to make sure their schematic isn't wrong there too.

[drbassman]

well, this is getting over my head!

[chromium]

Doc-

Without getting into all the minutiae, my hunch is this (and I could be completely wrong here  ):

- Your inductor is original, but differs from mine (probably Gibson just using what they had in the parts bin)
- The black wire is definitely for ground
- Your red and green wires offer two different inductor values, unlinke mine - which only offers one (one wire).
- Either the red *or* green wire could be used as your other (non ground) connection - and each would probably result in a different tone for the choke circuit.  (I suspect one of those wires gives something like half the inductance value of the other).

This pic from Jules' site shows more of what my inductors look like.  I remember the EB-2D inductor being similar to my EB-3, in terms of only having two wires coming out of the tin:




What I would suggest is, when the time comes:  wire it up and test it outside of the bass first, comparing the tone to your other EB-2, and let your ears be the guide of which inductor connection - the red or green wire - to use permanently.

Hope that helps clarify my thoughts.  If you really want to get a headache, just think of all the wiring and tonal possibilities using a switch (maybe a rotary, like these L6-S switches I bought!  Give it an ES-345 vibe...) that could exploit all the sonic options in my bass PLUS this possible "extra" choke value with your inductor!   Statictically speaking, your setup time (laboring over that perfect tone) would probably start to eclipse that of most guitar players! 

[drbassman]

Well, that make sense Joe.  I might be able to see if one inductor wire has been soldered and the other not.  I'll check and see.  I think your theory sounds pretty plausible knowing how Gibson operated back then!  Thanks for digging into this for us!

[Granny Gremlin]

I would guess that the 3rd wire was a ground for the sheild in which the inductor lives. Remember that older choke coils (on series 1 EB3s anyway) had a bit of metal leaf soldered on with 2 holes drilled to fascilitate mounting accross 2 pot shafts.  This would have the additional effect of connecting the choke case to the pot case which is connected to ground, making the third wire unnecessary.  ... and by that I mean that I would agree that it's probably the original one (see the pics of the choke in the 1966 EB-2 Wiring - the PO screwed with this too much! thread - also 3 wires). Neither series 2 EB3s nor Rippers even have sheilds on the inductor if that gives you any idea of how vital a connection Gibson considered it to be (I see plenty of value in it, mind).

Chromium, it occurs to me just now that your 3 way toggle mod would be an excellent opportunity to get that damn series resistor out of the circuit.   

Yes, the inductor apparently really is 15 H (I was thinking that is was meant to be 15mH for the longest time, as Gibson and labelling/QCing things properly is iffy, and 15 H is really HUGE) - see my post in the thread linked above for details. IIRC, 1.5 was what they used on the guitar varitone (i.e. Lucile) which makes perfect sense (rolloff point exactly an octave up from the EB choke) - realising this is what initially made me stop thinking the EB2 diagram was mislabled.

As you suggest, the purpose of the 3rd wire can be checked with a multimeter (or a battery + flashlight bulb) - check for continuity between the inductor casing and the 3rd wire to confirm my hypothesis.

[drbassman]

Thanks guys.  I'll get the meter out and see what comes up.  This is a real challenge for me!

[drbassman]

Hi Guys, I'm gonna revive this thread.  I put this bass on the back burner last year and now it's almost ready for paint.  So, I thought I'd ask a couple questions on the wiring.

I 'm going to try and use Joe's mod that he posted above.  I'm just not sure what to do with the two long wires coming out of the choke. I'll check their impedance later today and get back to you for some more advice.  

The PO was a real winner.  The pup and wiring were probably not from this bass.  The pup had the bracket on the bottom and didn't fit the cavity.  The pots and harness don't match up to the holes in the body.  The whole thing's a disaster.  I'll be taking it all apart and starting from scratch!

ADDITION:  Decided to screw work for a few minutes and tested the stuff.  The pup is 28.7k, so that's typical.  The choke gives a  .81 reading off the green wire and the long purple wire intertwined with the green one is dead, no reading at all.  So that makes my choices easier, no?

[eb2]

Not to stir up a hornet's nest, but did you see that EB-0 mod on Jules' board?  The last guy who posted seems to understand these things pretty well too. 

Me, I hope the choke is still hooked up, but if it isn't, good too.  I just feel like I should be wearing a lead apron over my nuts when I see them.

[uwe]

"lead apron"

File under "assless chaps".

[chromium]

Not to stir up a hornet's nest, but did you see that EB-0 mod on Jules' board? 

Just looked and saw that mod- that's a good idea.  That would give you variable amounts of choke, rather than just the on/off extremes.  In schematics for the Howard Roberts, L6-S, others(?)..  I noticed Gibson did something similar- where a pot controlled how much signal was bled thru a tone choke to ground.  That's basically what's going on there.

[drbassman]

Just looked and saw that mod- that's a good idea.  That would give you variable amounts of choke, rather than just the on/off extremes.  In schematics for the Howard Roberts, L6-S, others(?)..  I noticed Gibson did something similar- where a pot controlled how much signal was bled thru a tone choke to ground.  That's basically what's going on there.

Does this make sense Joe?  "Decided to screw work for a few minutes and tested the stuff.  The pup is 28.7k, so that's typical.  The choke gives a  .81 reading off the green wire and the long purple wire intertwined with the green one is dead, no reading at all.  So that makes my choices easier, no?"

[Highlander]

This is really "late to the party", Joe, but considering your original post... those switches can be stripped down, usually, and it would be (possibly, not having seen original) easier to remove leaf 4 altogether than to risk damage to the remainder...?

[chromium]

This is really "late to the party", Joe, but considering your original post... those switches can be stripped down, usually, and it would be (possibly, not having seen original) easier to remove leaf 4 altogether than to risk damage to the remainder...?

That's true- you can probably pull the switch apart and just remove that prong altogether.  A "regular" DPDT switch would do the job as-is too.  I just like the springy feel of those pickup selector switches. 

[chromium]

Does this make sense Joe?  "Decided to screw work for a few minutes and tested the stuff.  The pup is 28.7k, so that's typical.  The choke gives a  .81 reading off the green wire and the long purple wire intertwined with the green one is dead, no reading at all.  So that makes my choices easier, no?"

Yeah there's no harm in trying it like that.  The inductor should just have a wire going into the coil, and one coming out.  If you get some resistance reading across two of the wires, then those are probably the choke wires. 

I think Jake's hypothesis was right about that third wire - probably just a ground wire for the choke's metal enclosure.  You could always check that by measuring resistance from the enclosure to the end of that third wire.  Little or no resistance reading there, and an infinite resistance reading (i.e. no connection) between that wire and the other two choke leads would tell me that it would be ok to ground the "mystery wire".

[drbassman]

I think I would just like to use a DPDT push button switch.  Could I use one of the stomp pedal switches that's an "on-on" configuration?