Combined Passive Jazz Pickup Sound

[Babaluma]

i play a standard jazz bass, with lindy fralin jazz pickups into an avalon u5 d.i. into a chandler germanium compressor, and i love the tone!

recently i've been wondering what would be the technical explanation for the difference in sound you get with both pickups set to the same level. with only the bridge pickup you get a clean mid range sound, with only the neck pickup you get a full warm sound, but there is something tonally VERY different about the sound of the pickups combined.

i've often heard it called an "out of phase" sound, and sometimes a "scooped mid" sound, but i want to know technically/theoretically how and why it sounds that way, and the actual difference in the frequency response.

are some pickup settings used more for certain styles of music? i have to admit i generally like the sound of the pickups on their own more.

thanks in advance,

gregg

[idoru]

I'm a little hazy on this now, I used to have a link to a great site which explains this in detail... I just don't remember the technical side of this at all!

Whenever you have two pickups wired in parallel (or series), you get phasing cancellation of some frequencies dependant on where the pickups are. On a Strat for example, the bridge + middle setting is famous for it's "quack". Compare that to a Telecaster, where there's not so much phase cancellation & you get more of an even balance of the two tones. When the coils are next to each other like in a humbucker, you lose more top end.

There's other effects too; something about the coils loading each other down and acting as hi cut filters to each other. Somebody here will know the details I'm sure

Back to a J bass: since the bridge pickup doesn't produce anywhere near as much bass as the neck, and the neck doesn't produce as much treble as the bridge pickup, those two extremes are relatively untouched. Rolling back one of the volumes fractionally removes a lot of that cancellation, and restores a bit of the apparent volume as you've probably noticed

So yes, it is a phase cancellation effect which is causing a mid scoop. Wiring a pickup "out of phase" is when you swap one of the hot leads for ground, causing a lot of phase cancellation. Very thin & quacky tone that guitarists like for overdriven solos.

Classic J bass tones:

Reggae: Neck pickup, tone rolled all the way off.
Slap: both pickups dimed.
Fingerstyle / fretless / funk: bridge pickup soloed.

Myself, I favour bridge on full, with the neck rolled back to open up the tone for fingerstyle, and the other way around if I'm playing with a pick.

c-

[Babaluma]

hey idoru,

thanks for all the info, that's great!

i'm considering fitting a series/parallel switch for even more tone. btw does anyone know of any online sound samples of these different pickup tones on a jazz bass? i would love to hear what the series setting sounds like!

i play a lot of dub, so for that i obviously use the reggae setting you mention. i always play fingerstyle, so if it's not dub i'm playing then i think my favourite tone is the neck pickup soloed and the tone about half rolled off.

[Derek Kiernan]

A large part is where the resonance peak is located. This is why the sound of pickups fully buffered individually by a preamp (such as Audere) will not sound the same mixed as in a passive setup.

In a passive setup, the inductance of the pickup(s) interacts with capacitance to determine the resonance. The most substantial capacitance is usually in the instrument cable, but a tone pot turned down fully changes the sound by adding capacitance as well.


When you have both volumes on full, the inductances are added in parallel in this fashion: L = (L1*L2)/(L1+L2). Because this results in lower inductance than both pickups individually, the capacitance doesn't react as much and the resonance peak goes up higher, making the sound "thinner" without the lower resonance. The smaller inductance will give you less inductive reactance, resulting in better preserved highs, even if you were to add additional capacitance to drop the peak to the same place. The now high resonance peak will also likely make the sound bright.

When the volumes are not both on full, the pickups will load on each other and prevent true individual selection, largely contributing to the muted highs when you roll off one pickup. The range of mixing is actually very limited to the nearly fully on part of pots' tapers. Using a 3 way switch (doable with two volumes) allows individual selections without this effect. With both volume pots on full, the higher peak location will generally result in less voltage output and move a warm resonance to a bright one, which accounts for most of the sudden change you hear with both pots open.

[Babaluma]

thanks derek, that's a great explanation.

i use very short lengths of mogami 2554 cable with good quality neutrik jacks that i put together myself, so hopefully cable capacitance isn't too much of an issue as far as my tone goes (i did notice a big difference in quality, especially the highs, after making my own cables).

i've noticed how the almost "wah wah" type effect of twiddling one of the pickups volume pots only works in the top 10% of the pots travel, even with audio taper pots. it would be nice to get that effect through the whole of the pots travel.

is it really true that turning down both pots, but keeping them at the same level, will give you a different tone from when they are both on full? surely it's just a quieter version of the same? i've experimented and can't really hear a difference (except that it's quieter).

[lundborg]

Originally Posted by Babaluma

thanks derek, that's a great explanation.

i use very short lengths of mogami 2554 cable with good quality neutrik jacks that i put together myself, so hopefully cable capacitance isn't too much of an issue as far as my tone goes (i did notice a big difference in quality, especially the highs, after making my own cables).

i've noticed how the almost "wah wah" type effect of twiddling one of the pickups volume pots only works in the top 10% of the pots travel, even with audio taper pots. it would be nice to get that effect through the whole of the pots travel.

If you enjoy experimenting with electronics,
try adding a 10 times larger resistor between ground and the
previously grounded lead of the pot, and add a 10 times larger
capacitor in parallel with the old cap.
And use a dual pole switch to go back to "normal".

Originally Posted by Babaluma

is it really true that turning down both pots, but keeping them at the same level, will give you a different tone from when they are both on full? surely it's just a quieter version of the same? i've experimented and can't really hear a difference (except that it's quieter).

With both pots at half speed, you'll have 125 K in series with
each pickup, and 125 K to ground, instead of just 250 K to
ground (full setting). This will shift the cutoff frequency of the (low pass) tone circuit upwards. If you have a low tone setting, you should be able to notice.

/Tomas

[Babaluma]

wow! thanks for the info tomas! i'll give it a go tomorrow when i can blast things (it's late here now), i think when i tried it before it was with the tone fully up, so it'll be interesting to see if i can hear a difference with the tone control down.

might have a go at your electronic suggestion at some stage too!

[Stealth]

Originally Posted by lundborg

If you enjoy experimenting with electronics,
try adding a 10 times larger resistor between ground and the
previously grounded lead of the pot, and add a 10 times larger
capacitor in parallel with the old cap.
And use a dual pole switch to go back to "normal".

What would the effect of this be? A more "receptive" volume control that lets you "wah" it easier?