Volume Cut w/Both PUPs Open

[hairscrambled]

If this topic has been covered please tell me what to search for.

I just wired a friend's J Bass with the new Joe Barden pickups. The Bardens are very similar to Fenders except that common and bare grounds both go to the pot cover. Now however, with both volume controls open there is about 10db of reduction in the volume. Roll either volume back even a little and the overall volume is restored.

My first inclination is to reverse the polarity of one of the pickups but before I do this I'd like to get input from anyone that has had this experience.

Thanks.

[Fretlessboy]

This is the humbucking nature of jazz bass pickups. They are wound to be humcancelling with both full on...when the hum gets cancelled, so does signal

[Koeda]

Wouldn't reverse the leads. Heard this is due to the pickups loading each other. Found a fix that seems to smooth out the problem and on the side made the tone dial in better as well. Have used this solution on a number of double pickup basses with sucess. Add a 47K resistor on each hot tab of the pickup before the volume or blend pot. Source was here:
http://www.guitarnuts.com/wiring/stockgibson.php
David

[niftydog]

That's a damn good article, Koeda, thanks for posting it.

Everyone should read it!

[DavidRavenMoon]

If the tone thins out (you lose low end) with both pickups on, then they are out of phase. It has nothing to do with them being hum canceling, since the Bardens are dual coil humbuckers, and they don't work like single coil Jazz bass pickups.

And even with a Jazz bass, the noise is canceled because each pickup is opposite polarity (either by wiring it reverse, or winding it reverse) from the other as far as the noise is concerned. But since each pickup has opposite magnetic polarity, they are in phase to the strings. So the noise cancelation does not also cancel the string's signal. Any volume drop is from loading, but it shouldn't be much.

The article listed at guitarnuts is about Gibson wiring. Jazz Basses have their pots wired differently, so that article doesn't apply. On a Les Paul, when you turn one volume down it turns down both pickups. Jazz Basses don't work that way.

I think the issue here is the pickups are out of phase. Loading shouldn't cause that much of a drop in volume.

[niftydog]

Originally Posted by DavidRavenMoon

The article listed at guitarnuts is about Gibson wiring. Jazz Basses have their pots wired differently, so that article doesn't apply.

I would disagree - the principles still apply. Going by the fender american jazz bass wiring diagram, when both volume pots are maxed out the pickups are effectively wired directly in parallel which will produce the loading effect described in the article.

Surely if the issue was due to the wiring being out of phase the OP would be complaining of a terrible, weak sound.

Perhaps 10dB is an overestimate?

[DavidRavenMoon]

Originally Posted by niftydog

I would disagree - the principles still apply. Going by the fender american jazz bass wiring diagram, when both volume pots are maxed out the pickups are effectively wired directly in parallel which will produce the loading effect described in the article.

Surely if the issue was due to the wiring being out of phase the OP would be complaining of a terrible, weak sound.

Perhaps 10dB is an overestimate?

What principle is that? The article was talking about the problem with one volume control turning down both pickups. Go back and read it again. It said nothing about one pickup loading another. On a Gibson, the pickup is wired to the outer lug, while the output is wired to the wiper. When you turn down one pot, it shorts out both pickups because it is shorting the input of the amp to ground.

On a Jazz Bass, as well as a Ric, the pickup is wired to the wiper, while the output is from the outer lug, so turing down one pickup doesn't turn down both of them because it is shorting the pickup to ground. The input of the amp is isolated by the value of the pot. But doing it this way dulls the tone of the pickups, unless you have the volume pot on 10.

They aren't talking about one pickup loading the other. There's also a typo in the article where they say:

A lot of people don't wire the volume controls properly on these guitars. If you wire them the way a Fender guitar is wired then the controls are "coupled" and either volume control will completely kill the output of both pickups when it is turned down all the way. Actually, Gibson has been wiring guitars this way for at least a couple of decades now, but that is unfortunate.

Obviously they meant to say "if you wire them the way a Gibson guitar is wired" since Fenders with two volumes, like a Jazz bass are not wired like the schematic shown.

Now notice they are talking about the controls being "coupled" and nothing about the pickups. But in the usual guitarnutz fashion, they got it wrong. The way Gibson does it is the correct way to wire a passive volume control. The Fender Jazz Bass way is actually incorrect, but in the case of wanting to mix two pickups passively, it's the only way to do it.

The reason why it's wrong is when you don't have the volumes up full, you get a lot of loading, more so than with the Gibson way. You can hear it if you turn both pickups off, and then turn one up just a hair. It's very dull sounding, and that's only ONE pickup on.

This has nothing at all to do with two pickups in parallel loading each other, and you can also prove that by wiring the two pickups up directly to a switch and then to the output jack, with no controls. When you switch them both on, you will get the parallel coil effect, i.e., if each pickup is 10K, then in parallel you get 5K.

It has nothing to do with the pots. A 250K pot is a negligible load to a 6K to 8K pickup, but the load does shape the resonant peak of the pickup. Most people like that tone, and that's why they like passive pickups.

To really get around all that, you need to buffer the pickups, preferably each having it's own buffer, and then mix them. You get no parallel coil loading, and no dull sound when you turn down a volume control.

[McSpunckle]

My PJ setup does that. It doesn't seem all that much quieter, but it's a bit brighter. Not out-of-phase brighter... but slightly brighter.

For the record, when the article was talking about "wiring like a fender" they weren't talking about a Jazz bass. They were talking about a Strat with a master volume... which has the pickup wired to the outer lug and the output wired to the wiper.

Jazz basses are wired mixer style, just like they were showing a Les Paul should be wired. That way, turning one all the way down won't kill all the signal.

Some people wire LPs "incorrectly" on purpose because it allows the switch to be used as a kill switch... but that's another issue.


It's not uncommon for 2 pickups to be quieter than 1 pickup. There are cancellations there. Every pickup is a tuned circuit that can act as a filter on the other one. It just happens.


I'll try to explain this... then I'll quote where I'm getting it from.

In a typical guitar humbucker (same way a Jazz set works, but they're farther apart), putting the coils in parallel will raise the resonant frequency (make it brighter) more than only using one coil will. So, it makes sense that using only 1 jazz pickup could be a bit beefier and louder than both.

"Normally, both coils are switched in series. Switching them in parallel cuts the inductance to a quarter of the initial value, so the resonant frequency (all other factors being equal) will be twice as high. Using only one of the coils halves the inductance, so the resonant frequency will increase by the factor of the square root of 2 (approximately 1.4)." http://buildyourguitar.com/resources/lemme/



Ok, so basically, your bass is probably fine. Sadly, I don't have a jazz bass to test this... but I can get a couple or reversed single coils to try it...

[Koeda]

Hey hey,
To get back on track.... Granted the Gibsons are indeed wired dif but I posted the article in ref to pickup loading only - that is the principloe that still applies to the Jazz. Skip down to his last response and the last couple paragraphs of the article only for this principle. From the original question - that sounds to me like the issue rather than a phase issue. If they are single or split - I have found pickup loading still occurs when both vols are maxed out. This I have noticed in the stocker singles, Model J's and the Bart classic splits. When the resistors are added as in the article - there is no 10db drop when both pickups are at full vol. The tone range also seems to smooth out over a larger range on the sweep of the knob. Especilly on the hb jazz pu's - seems the tone knob had little effect til almost at full off before adding the 47k resistors. This is just my experience so ymmv. Aloha,
David

[wyleeboxer]

Ok didnt read all the posts here, however, I just rewired my Shecter jazz bass which has passive J neck and MM bridge SD pups. My bass was doing the same thing, low output and thin sound when both pups where on full. I simply rewired the front J neck pup, that is reversed the postiive and negative wires (5 min to do) and bammm the bass was brought back to life, even now has a great slap tone with both pups on full!

[DavidRavenMoon]

Originally Posted by McSpunckle

My PJ setup does that. It doesn't seem all that much quieter, but it's a bit brighter. Not out-of-phase brighter... but slightly brighter.

The pickups are unbalanced enough to not kill the common frequencies between the two. Having two different sounding pickups helps.

Originally Posted by McSpunckle

For the record, when the article was talking about "wiring like a fender" they weren't talking about a Jazz bass. They were talking about a Strat with a master volume... which has the pickup wired to the outer lug and the output wired to the wiper.

Right, and that's exactly the way a Les Paul is wired, except a Strat only has one volume. A P bass is wired like a Strat also. So using that as an example made no sense. That's the correct way to wire a volume control, but it doesn't work right with two volume controls. The article was about how to stop having one volume turn down both pickups. I wouldn't put too much credence in anything on that site.

Originally Posted by McSpunckle

Jazz basses are wired mixer style, just like they were showing a Les Paul should be wired. That way, turning one all the way down won't kill all the signal.

Some people wire LPs "incorrectly" on purpose because it allows the switch to be used as a kill switch... but that's another issue.

Gibson does it that way because it gives the best tone when a pickup is turned down. I don't think they intended people to use it as a kill switch since people didn't play that way back in the 40's and 50's.

I wired up my Les Paul with one master volume, two tones and a varitone. I think the two volumes on a LP is dumb.

Originally Posted by McSpunckle

It's not uncommon for 2 pickups to be quieter than 1 pickup. There are cancellations there. Every pickup is a tuned circuit that can act as a filter on the other one. It just happens.


I'll try to explain this... then I'll quote where I'm getting it from.

In a typical guitar humbucker (same way a Jazz set works, but they're farther apart), putting the coils in parallel will raise the resonant frequency (make it brighter) more than only using one coil will. So, it makes sense that using only 1 jazz pickup could be a bit beefier and louder than both.

"Normally, both coils are switched in series. Switching them in parallel cuts the inductance to a quarter of the initial value, so the resonant frequency (all other factors being equal) will be twice as high. Using only one of the coils halves the inductance, so the resonant frequency will increase by the factor of the square root of 2 (approximately 1.4)." http://buildyourguitar.com/resources/lemme/

Right, two coils in parallel gives you half the DC resistance. Inductance is more about the core of the coil. Pickups are not really inductors, so that formula is not exactly right when it's applied to pickups. But two coils in parallel have lower impedance. Assuming the load on the pickups remains constant and is a high impedance, the change of resistance between series and parallel will alter pickup impedance and tone as well as the output level of the pickups with the series connection being louder.

The distance between the coils is a separate issue, and that's where the cancelations and reinforcements change. The distance between the coils shift the notch frequency. Humbuckers tend to cancel the highs a bit because those harmonics are close together. If you move the two coils farther apart, like on a Strat, you get a different cancellation.

Originally Posted by McSpunckle

Ok, so basically, your bass is probably fine. Sadly, I don't have a jazz bass to test this... but I can get a couple or reversed single coils to try it...

You get a slightly scooped tone with both pickups on, but you shouldn't get a huge volume change. Of course it helps when the bridge pickup is wound a bit hotter, so that the two pickups have a more balanced output.

Here's an example. This is not a Jazz Bass.. this bass has two humbuckers wired up with two 500K volumes mixer style. The pickups sound different, but the overall volume doesn't change too much.

First is the neck - both - bridge - both - neck.


Level Test

[niftydog]

Originally Posted by DavidRavenMoon

Go back and read it again. It said nothing about one pickup loading another.

Yes it does:

Originally Posted by guitarnuts

With both volume controls at maximum the two pickups are wired directly in parallel and each applies a fairly high load to the other. As soon as you back either volume control off even just a little you throw 100k or so of resistance between the two pickups which isolates them so they no longer load each other.

Originally Posted by DavidRavenMoon

On a Gibson, the pickup is wired to the outer lug, while the output is wired to the wiper.

Not according to the guitarnuts article. However, I'm only referring to the principles described in the article, not the specifics about Gibson guitar wiring. I'm not talking about one volume knob turning down both pickups, I'm referring to the loading phenomenon.

Originally Posted by DavidRavenMoon

...a Jazz bass are not wired like the schematic shown.

That's true, but if you take a look at this diagram from a Fender American Jazz Bass you can clearly see that with both volumes at max, the pickups are effectively wired directly in parallel which, whether you believe in the loading phenomenon or not, is the perfect situation to reproduce it.

Originally Posted by DavidRavenMoon

This has nothing at all to do with two pickups in parallel loading each other...

To really get around all that, you need to buffer the pickups, preferably each having it's own buffer, and then mix them. You get no parallel coil loading...

Are you referring to two different problems with two different solutions?

The simple solution is for the OP to flip the wiring of one of the pickups and report back on the results. If I've interpreted your posts correctly (not loading, not pot values etc.) you believe that would fix the problem, correct? I think that will just make the terrible, feeble sound of two pickups with their signals out of phase.

[DavidRavenMoon]

Originally Posted by niftydog

Yes it does:

I didn't read all the way to the bottom. I read enough nonsense to not have to bother.

Originally Posted by niftydog

Not according to the guitarnuts article.

The schematic in the article is not how a stock Gibson is wired up.

That web site is full of incorrect information. Just keep that in mind when you read any thing there. Most of it is wrong.

Originally Posted by niftydog

That's true, but if you take a look at this diagram from a Fender American Jazz Bass you can clearly see that with both volumes at max, the pickups are effectively wired directly in parallel which, whether you believe in the loading phenomenon or not, is the perfect situation to reproduce it.

You are misunderstanding how the whole thing works. Forget the pots. They have nothing at all to do with wiring two pickups in parallel. A Gibson LP also wires both pickups in parallel. The pots have no affect on how the impedance changes from parallel coils.

I gave you two things to prove that. Bypass the pots and wire the two pickups to a switch. Now listen to the pickups in parallel. How they load each other has nothing to do with the pots. You can also wire them up like Gibson does. They will do the same thing when you switch them both on.

Install a buffer after the pots, and now things change quite a bit.

If you wire the two pickups in series, they still load each other. You can hear how they sound much darker because the impedance is higher now.

Did you listen to the sound clips I posted? Do you hear a volume drop? I sure don't. I do hear three different tones though. Those pickups are made to work together well. I know because I made them.

And yes, we are talking about two different problems. People rewire Les Pauls so that both pickups don't get shut off when you turn down one of them. The reason that happens is because turning down one of them shorts the amp's input to ground.

The other issue is that the reason Gibson wires the guitar that way is because wiring it like a mixer loads down the pickups when the control is less than full on. At full on it loads as much as the rated value of the pot, i.e., 250K. Two 250k pots in parallel are a load of 125K on the pickups. This is the same if it is a Gibson or a Jazz Bass.

There is no way to have two pickups on in parallel where they are not interacting with each other.

Originally Posted by niftydog

The simple solution is for the OP to flip the wiring of one of the pickups and report back on the results.

The wiring how? Reverse the phase? Or wire the pot the other way. The first will likely make a big difference, and the later wont do a thing.

Originally Posted by niftydog

If I've interpreted your posts correctly (not loading, not pot values etc.) you believe that would fix the problem, correct? I think that will just make the terrible, feeble sound of two pickups with their signals out of phase.

To me it sounds like the pickups are already out of phase. The leads to one needs to be flipped.

Two passive pickups in parallel reduce the impedance by half, and that presents less current to the amp, so there is a slight volume drop. But now a big drop. I proved that with the sound clip I posted.

[niftydog]

Originally Posted by DavidRavenMoon

You are misunderstanding how the whole thing works. Forget the pots. They have nothing at all to do with wiring two pickups in parallel.

I gave you two things to prove that. Bypass the pots and wire the two pickups to a switch. Now listen to the pickups in parallel. How they load each other has nothing to do with the pots.

Install a buffer after the pots, and now things change quite a bit.

I think we're actually agreeing with each other here but you seem to have misunderstood my position.

I'm not talking about the effect the pots have on the circuit except to say that when the pots are maxed out they ARE effectively bypassed - leaving the pickups wired in parallel just as you've described above.

You seem to agree that parallel loading does occur, and that one way you can resolve it is by buffering the individual pickups. But then you seem to assert that parallel loading doesn't occur by sighting your test of your own pickups.

While it's not quite the same as having dedicated buffers, placing a resistance between the two coils would also have some affect on the loading phenomenon.

But all this isn't helping the OP sort out his issue. I would like to see him try Koeda's suggestion of putting a resistor in series with each pickup, just to see what it does. I would also like to see him flip the wires on one of the pickups to see what that does.

[niftydog]

Originally Posted by DavidRavenMoon

The wiring how? Reverse the phase? Or wire the pot the other way. The first will likely make a big difference, and the later wont do a thing.

The pickup wires.

Again, I'm not talking about the pots - you seem to be confusing my opinions with those of the guitarnuts author.

[DavidRavenMoon]

Originally Posted by niftydog

The pickup wires.

Again, I'm not talking about the pots - you seem to be confusing my opinions with those of the guitarnuts author.

OK, then we agree. I think the pickups might be out of phase with each other.

[Koeda]

Either way - it is easy to find out. I'm gonna put my $ on a pair of 19 cent 47k 1/4 watt resistors from Radio Shack tacked on to the positive leads of the pu's. So hairscrambled get on it and let's put it to rest!
David

[DavidRavenMoon]

Originally Posted by Koeda

Either way - it is easy to find out. I'm gonna put my $ on a pair of 19 cent 47k 1/4 watt resistors from Radio Shack tacked on to the positive leads of the pu's. So hairscrambled get on it and let's put it to rest!
David

I do this with some of my basses, but I put the resistors after the volume controls. In my case these are active basses. I use 10K resistors.

keep in mind that the resistors might change the tone of the pickups.