Wiring Question

[Scott Gray]

First I would like to say this site is incredible! I just discovered it the other day (and at just the right time) I am attempting my first build (an extended range fretless bass). Everything is looking pretty good so far despite my multiple attempts to destroy it.

The pickups I purchased are Bartolini X45 series and I want to wire a 2 volume 2 tone setup. It's a little unusual but I think it should allow for better tonal control.

The schematic that came with the pickups seems to be kind of generic and references both guitars and basses.

Here's what I came up with for wiring. Please ignore the overlapped wires, drawing wiring diagrams is not my day job.

Does this schematic look correct? Are there any issues with both PU's wired direct to the output or should there be something to isolate each signal from the other (diode?) And most importantly, my schematic is slightly different from Bartolini's, and I've never ruined a set of pickups before but I don't want these to be the first.

Thanx

[Greg Robinson]

Hi Scott, and welcome.
Well, that's pretty good for a first attempt, but there is one problem. The way the volume pots are connected is interactive: turning down one control will cut off both pickups. This happens on Les Paul's and SG's, because the volume controls are connected the same way, but because they also have a switch, it only happens when both pickups are selected. Because you do not have a switch, both pickups will always be selected, so the volume controls will always interact.
It's easy to fix though, simply switch the contact that the pickup enters with where the signal exits, that is the bottom two lugs of the two volume controls in your diagram. In this configuration, the two volume controls will not interact. This makes the wiring basically a Jazz-Bass style, only with two tone controls.

Good luck!

[Scott Gray]

Greg,

Thank You, and yes the old early 60's J Bass configuration is what I'm trying to get.

So, would this be correct? Just moving the pickup + wire but still leave the + connection from the volume to tone where it was?

[Chuck Raudonis]

Hi Scott, and welcome.
Well, that's pretty good for a first attempt, but there is one problem. The way the volume pots are connected is interactive: turning down one control will cut off both pickups. This happens on Les Paul's and SG's, because the volume controls are connected the same way, but because they also have a switch, it only happens when both pickups are selected. Because you do not have a switch, both pickups will always be selected, so the volume controls will always interact.
It's easy to fix though, simply switch the contact that the pickup enters with where the signal exits, that is the bottom two lugs of the two volume controls in your diagram. In this configuration, the two volume controls will not interact. This makes the wiring basically a Jazz-Bass style, only with two tone controls.

Good luck!

Let me see if I understand what you're proposing. You want to move the line coming from the pickup to the center lug (the wiper) and the output to the jack to the bottom lug. Correct?

[Greg Robinson]

Scott,
Yes, that's perfect, exactly what I meant. This will allow you to dial in the level of both pickups, without effecting the other. Both ways of hooking up a pot as a volume control work, but the first one grounds the output, where the second one grounds the input. The first method is preferred when used as a master volume control because it grounds the output and cuts noise completely save for any minor impedance in the cable and wiring that creates resistor noise and can pick up interference, whereas the second method, while allowing individual sources to be mixed passively without interacting, leaves the output ungrounded, with a large impedance hanging off it, and the resistor noise and higher susceptabilty to interference that comes with it.

Hi CRaudonis,
Yes, that's correct, refer to the second diagram that Scott put together above.
Also, please note that we require the use of full names on this forum. Please let me know your first name either here or in a private message, and I will update your registration and login information for you (you are not able to make these changes to your account yourself). Thanks.

[Scott Gray]

Greg,

Again Thank You, I almost forgot, but do I need to run a ground wire to the bridge or do today's PU's and pots even need one? I'm pretty sure I've read that some pickups specify do not ground. But for the others is it still required, optional or not needed?

Scott

[Greg Robinson]

All magnetic pickups should have the strings/bridge grounded, otherwise noise is picked up. Some pickups, especially low-inductance active pickups, are less susceptable to this interference than others, and some manufacturers (such as EMG) suggest you do not ground the strings. This is partly because of some people that recommend using a capacitor or resistor/capacitor combination to isolate the strings from the amplifier, supposedly to protect against electric shock or electrocution caused by faulty equipment or mains wiring. However, this is essentially the same practice as the "death cap" used before the advent of polarized power sockets and the use of safety ground, which is now ILLEGAL almost globally because of the inherent dangers it allows. While it does offer some protection, it is not a catch-all, and leads to complacency and a false sense of safety, that could cause people to ignore real problems that still present a very real danger. The other problem with this concept is that failure modes are not considered, with many advocates of this concept recommending using low-voltage rated capacitors, so that the capacitor will "act like a fuse". This is NOT how a capacitor works, it is NOT a fuse, and many types of capacitors, particularly the plastic types most often recommended for this application will fail SHORT, not open, providing you with no protection at all.

The only way to be sure of your safety is to make sure your equipment is in good condition, with a 3 conductor polarized cord, and to use a power socket tester on any and every power point you plug into. Anything less is gambling with your life, regardless of any "safety capacitor" you may have in your guitar.

[Joshua Levin-Epstein]

Scott, You cab simplify your wiring (slightly) by tying the outside lugs of the volume controls (the ones going to the jack) together and then tying one to the output. That way you won't have two leads going to the hot side of the jack. Another fine point is the tone controls will bleed highs from the output of the two pick ups in whatever combination. So if both pick ups are on equally, one tone all the way off, you won't be getting one pick up full tone and the other pick-up tone off. The original Jazz Bass wiring (with concentric knobs) attempted to minimize the interaction of the tone controls with resistors. Some people feel this adversely affected the sound (One of Jaco's basses was originally concentric). If you want to isolate the tone controls, you can run stereo, but I think that is a pain (two output jacks or a special cord, two amps or a two channel amp).

And yes, ground everything.

Joshua

[Scott Gray]

So you're saying this configuration would basically work as if there is just 1 tone control? My whole thought process was to have 2 pickups able to have their own volume and tone independent of each other.

I'm not even sure if I would like or use that feature, but it seems reasonable (to me) that it would allow for more tonal control or spectrum.

[Greg Robinson]

The two tone controls will have a certain degree of independence, but only when the volume controls are turned down less than full. When both volume controls are on max, both tone controls will effect both pickups equally, but if say, you turn down the neck pickup to half, then the neck tone will not have as much effect on the bridge pickup, but the bridge tone will still have full effect on the neck pickup (albeit with a shifted resonant peak) and vice-versa. But these differences are subtle, and you will likely not notice many subtleties to differentiate it from a master tone control. Although, it could be useful to set the tone for each pickup when choosing between them, but without a switch this is not very practical anyway.

The only way to achieve truly independent tone controls would be to add active electronics (a buffer), or I guess you could use isolation transformers, but that seems a little elaborate to me.

[Joshua Levin-Epstein]

I realized as soon as I hit "submit" that I might have been throwing some cold water. Sorry about that. If your bass is setup up for 4 controls, you won't be losing anything by wiring it with two tones and you'll be able to hear what we've been describing. One "experiment" you might try is plugging the bass (or something wired like a Gibson) in with everything at full. turn the bridge tone all the way down. Now tap on the bridge pick-up. As expected, the tone will be muted. Now tap on the neck pick-up. It too will be muted. Reduce the the bridge volume slightly and the tone returns to the neck pick-up. I'm sure i discovered that during a midnight wiring session and ranked myself with Mme Curie and Les Paul.

My preference is the 3 knob Jazz Bass wiring. I like to add a phase switch in fretless instruments.

Experimenting with wiring is pretty easy and you can do it without making a lot of sawdust and noise (note previous reference to midnight).

Joshua

[Scott Gray]

Joshua,

That's fine. Actually this is the kind of discussion I wanted to open up because I just had the 2V 2T idea and drilled my bass body before checking to see if it would work or what obstacles I would encounter.

But to my original question, (I assume bigger minds than myself have already addressed this) If you put a diode in both + output wires to the jack would that act as a check valve to prevent one circuit from "talking" to the other?

And a phase switch... I'm intrigued. Would that be an ON / OFF type switch, or could it be accomplished with say a 250K pot that otherwise has no real benefit to the guitar?

[Joshua Levin-Epstein]

Scott, I've never tried to isolate the tone controls, so someone else will need to answer that question. People typically use a mini switch (DPDT) for phase reversal and that would be much smaller than the barrel of your tone control. If someone walked into my shop and wanted a phase switch added to an instrument set up like yours, I'd replace one of the tones with a switching pot. No extra holes and reversible. I would also tell them that the pick ups will need to be at equal volume in order for the phase switch to be effective. Say you're playing with the neck pick up backed off a bit (typical jazz bass setting). You would need to raise the volume to full and engage the phase switch. By the way, you'll lose a lot of volume when you do this. I like this for soloing on fretless (though no one else likes me soloing on fretless, or anything else) but not as much on fretted. If you wanted to try this sound with buying any thing extra, reverse the leads on one of the pick ups. With everything on full, you'll be able to try the out of phase sound. If those pickups come with single conductor plus shield cable, you'll need to replace the that with two conductor plus shield. You don't want to connect the shield to the hot side of the output.

Have I muddied the waters sufficiently?

Joshua

[Joshua Levin-Epstein]

Sorry to be going on, but I didn't want you to think that the second tone control is superfluous. There will indeed be a change in tone if you roll both controls down.

Joshua

[Scott Gray]

That's funny. I've never heard anyone say "Scott, why don't you solo another 32 measures" either.

And yes, the pickups are 2 ? conductor (single "hot" wire and a braided ground around it) So I will most likely go with the original 2V 2T idea.

[Greg Robinson]

Adding diodes to any part of the circuit would make a poor mans clipping circuit, like a crumby stomp-box fuzz. Mostly it would cut out most of the signal. It wouldn't isolate the two tone controls from each other. Only way to do that in a practical manner would be to use active electronics.

[Scott Gray]

I figured that if it was that simple others would have already used that approach. But since the cavity is cut, holes are drilled and parts purchased, the 2nd wiring configuration will be fine.

And besides, this is a first attempt at building a guitar. If it plays and sounds good, then that's great. If not, future projects will have some modifications.

But again, Thank You both for sharing your knowledge and experience. This site is really cool. Clicking around I see that the members here are polite, professional and passionate about their craft... You don't see that on the internet very often.

Thank you

[Greg Robinson]

Glad to help Scott, and thanks!

[Scott Gray]

Greg,

One more question. The lacquer is dry and I just started wiring. The cavity that I cut is relatively small and the capacitors (Sprague Orange Drop) are quite a bit larger than I had anticipated. It will be a real squeeze to fit everything in there. Is voltage and size a real consideration for cap's? Or can I just look for the smallest .047 mfd rated for X volts I can find.

Any thoughts or recommendations?

Thanks,
Scott

[Mark Swanson]

Many types of caps will work, there are much smaller ones to be had and they'll all work well. If I were you I'd just get a ceramic or a mylar cap, very easy to fit in small places.