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Removed the Blend pot from my J

J

John Webb

Apr 20, 2006
1,095
554
#1
I have come to the conclusion that the two seperate volumes are there for a very good reason.

TONE!! :cool:

No matter how I adjusted the blend pot that I could not get the tone I wanted. In addition the loss of output was just not acceptable. :atoz:


I do not blame the vendor or the components as they are reputable and of good quality, this setup just ain't for me.

I gave it about 6 months and I'm back to stock now......what a difference!! ;)

It's a Fender J Bass again.:smug:
 
#3
Dogbertday said:
i imagine that it's the case becasue you can't have both of them wide open
Click to expand...

That is a myth--with a properly-wired blend pot, the center position is both pickups at 100%. :)

I think the difference in sound is that a vol/vol harness has 2 volume pots, while a vol/blend has 3 (the blend is 2 pots stacked on top of each other). All other things being equal, the extra pot "sucks out" a bit of output and brightness.
 
#7
When you have a blend pot, master volume, and master tone control, you've got essentially three volume pots. A traditional V/V/T set up only has two volume pots. The extra loading of the additional volume pot may cause enough audible changes to impact what you hear. Me, I had a passive blend on my fretless (until I put a Duncan pre-amp in it), in one of my Precisions, and on my Guild (althoug the Guild had active EMG PUPs). In no case was the small resultant treble loss critical to me. It's subtle, like the difference between having controls at all and having a true full by-pass (something else I had on two different passive basses).

Me, being a lifelong Precision and StingRay player find having one volume control to be a lot easier for me. So, a two PUP bass will have a blend pot for me. And again, it's simply NOT TRUE that a blend pot doessn't give you both PUPs on full. A real blend pot is ganged and made so that as you sweep from center to either extreme it turns DOWN a pickup. At center both PUPs are on full. As you sweep towards soloing the neck PUP, it's merely turning the bridge PUP down. At the extreme CW rotation the bridge PUP is completely out (well, as completely out as the circuitry allows- there's always some bleeding over). As you sweep back to center, it's rolling the bridge PUP back in until you get to center where both are on full. Then as you continue rolling the pot CCW, it's rolling the neck PUP off while leaving the bridge PUP full on.

I don't undestand why everytime the mention of a blend pot comes up, someone's gotta spout this nonesense like "i imagine that it's the case becasue you can't have both of them wide open" (sic).

jte
 
#9
Mushroo said:
That is a myth--with a properly-wired blend pot, the center position is both pickups at 100%. :)
Click to expand...

Depends on the taper of blend pot. Very often that is not the case.

Mushroo said:
I think the difference in sound is that a vol/vol harness has 2 volume pots, while a vol/blend has 3 (the blend is 2 pots stacked on top of each other). All other things being equal, the extra pot "sucks out" a bit of output and brightness.
Click to expand...

That's true.
 
#10
Stromrider said:
I prefer to just use a 3 way switch to select between one pickup or the other, or both. Then have a single volume pot and the tone control.
Click to expand...


same for me

PIC00013.jpg
 
#11
DavidRavenMoon said:
Depends on the taper of blend pot. Very often that is not the case.
Click to expand...

Hi David, are you saying that you personally recommend a blend pot that is 50%/50% in the center position, or are you just saying that you've encountered them in your travels? If you do use a 50/50 blend pot, what in your opinion is the advantage over 100/100?

I ask because, like JTE mentioned above, I don't understand where people are getting the idea that "you can't turn your bass up past half way if you have a blend pot." Since you have encountered this "very often," which builders specifically are using 50/50 blend pots and why?
 
#12
good point about the 50/50%. i never realised that. i think the way they are wired stock allows the impedances of each pickup to affect the other depending on the volume setting. that would change the tone. i have noticed the same thing on microphones, a high impedance mic into a low impedance input changes the frequency resopnse. johnny a
 
#13
Someone here posted a frequency sweep graph of some passive pickups at 90% on the volume pots and at 100%. When at 100% there was a pronounced peak in the frequency response. As soon as the pup was loaded with some resistance, the peak went away.

This is why many people prefer to have the dual volume pots at 8 instead of wide open - the sound is different, not just lower.

With the balance pots that are at 100% in the middle (Not ALL are) you cannot get the same sound as with 2 volumes at 8. Some pots are specially made to be 100% at center (Stewmac, for instance) and the normal stereo type balance control is the A and reverse A taper, with the 50% point to be specified at anywhere from 50-90%,

This is just a matter of taste - I prefer the sound at 8, without the peak.

Using passive pickups and variable resistors on the outputs is very complicated, as the impedance and loading changes constantly as the pots are moved. You are adding R (resistance) to the L (inductance) of the pup, creating a variable filter. You can only avoid these changes with a preamp to buffer the circuit so the pots don't affect the sound.
 
#15
Gio S said:
With the balance pots that are at 100% in the middle (Not ALL are) you cannot get the same sound as with 2 volumes at 8. Some pots are specially made to be 100% at center (Stewmac, for instance) and the normal stereo type balance control is the A and reverse A taper, with the 50% point to be specified at anywhere from 50-90%,
Click to expand...

Hi Gio, I know there are potentiometers on the market that are designed to have 50/50 volume in the center (instead of 100/100), and I am sure they have lots of applications. I guess my question is, who is using them as blend knobs in basses? Fender? Ibanez? Gibson? Sadowsky? Fodera? Or are we talking about the occasional person who builds a parts bass and orders the wrong pot for the job?

I guess I'm just trying to stamp out the misinformation that the average bass with a blend knob only gives you half volume in the center position. It comes up every single thread! If somebody can tell me, "actually, all _(insert manufacturer here)_ basses use the 50/50 taper" then I will shut up. :)

The rest of your post was interesting too. I know there are simple mods out there that prevent the treble from bleeding as you turn down the volume knob, but I like the idea that this phenomenon can be used musically. :)
 
#16
Mushroo - There are many different tapers available for pots. For example - go here
http://www.nobleusa.com/documents/EC_2007_JEA.pdf page 45

There are "A" taper pots for audio. The taper is sort of logarithmic, since that is how we hear. The taper is specified as 5A, 10A, etc. This the percent of total resistance at the 50% rotation point. The different value give a different "feel" to the sound as you rotate the pot.

"B taper pots are roughly linear - 50% rotation = 50% value. This is not usually used for audio, because all the action will seem to be at one end. This CAN be used for certain active electronics because of the circuit design.

A BALANCE pot is normally a A taper for one pickup and a reverse A for the other, so one gets louder as the other gets softer. Of course there are special design tapers as well, such as the ones sold by Stewmac where the taper goes to 100% at the center.

With a Blend pot using 2 A tapers, the center will have some loss, but how much depends on the taper. If it is a 5, then there is only a little loss at the center. If it is a Stewmac custom pot there is no loss at the center, but then you can't turn down each pup 50% to eliminate the peak in the response!

AS far as manufacturers using Blend pots - I would say that to MY limited knowledge, they are ONLY used with active electronics, because:
1. So that there is no loss in level (the electronics compensates for this)
2. So there is no change in sound quality as the Blend pot is turned (by changing the impedance in a passive system).

Whether there is 50% level in the center depends on the circuit design and the pot chosen by the design engineer - sorry!

Does this answer you question or just make more?
 
#17
Thanks Gio, that is really helpful and helps to clear up some of my misconceptions. I always assumed the Stew-Mac style pots were the industry norm.

FWIW, only one of my basses has a blend knob, and it is passive. However, it was one of only a handful of passive basses by a shop that usually makes active basses (with blend knobs), so it was probably a case of using the same parts rather than seriously debating the V/V vs. V/B issue.

I am still unclear on exactly which "taper" the various builders are actually using in instruments. Hopefully some of them will start to chime in. In the meantime, is there a way I can check the taper on my bass?
 
#18
The easiest way to do this is perhaps to open the instrument and see if it is marked on the back of the pot. It MAY say "5A250K" for example - 5A taper, 250K resistance. If NOT, you must disconnect the wires and measure it from the wiper to one side as you turn it with a good ohmmeter. The hard part is determining where 50% rotation is!

Is this important to know? You should be able to hear how much the volume of one pickup dips when you turn it from the end to center.

I tend to agree with you that your bass maker may use the 0 loss type of blend control. I am re-wiring my Fender PJ bass and will install one of the Stewmac pots for blend and see how it feels. However, my "gut" feeling is that a pot with 05 taper A and reverse A may sound and feel better. Back when I was really anal about such things I would bring the wires out under the pickguard with a connector and swap pots back and forth to see the difference! (not any more).

FYI - I also install a "mute" switch whenever I can to ground the output of the bass so you can set it down without any hum or noise problems. This is for passive basses. My old Hagstrom from the 70's had this and I can't live without it. I'm not yet sure if I can ground the output of active basses - I'll need to talk to the preamp makers first.
 
#19
Gio S said:
Is this important to know? You should be able to hear how much the volume of one pickup dips when you turn it from the end to center.
Click to expand...

No, it is not important to know, my only curiosity is for purposes of internet discussion! :)

I know the bass well (my main bass for 15 years) and it is consistent in output (and produces useful variations in tone) at all positions of the blend knob. I guess I just assumed all blend knobs worked this well!

Actually, there *is* a slight variation in output--the P pickup is slightly hotter than the J--but I would assume this has nothing to do with the blend knob.
 
#20
Mushroo said:
Hi David, are you saying that you personally recommend a blend pot that is 50%/50% in the center position, or are you just saying that you've encountered them in your travels? If you do use a 50/50 blend pot, what in your opinion is the advantage over 100/100?

I ask because, like JTE mentioned above, I don't understand where people are getting the idea that "you can't turn your bass up past half way if you have a blend pot." Since you have encountered this "very often," which builders specifically are using 50/50 blend pots and why?
Click to expand...

There are different blend pots. Some are audio taper, and reverse audio taper. Some are marked A/C and M/N.

I like M/N myself. It gets the level more-or-less all the way on in the middle. M/N seems to be what I've seen with Bartolini and Fender setups.

Stew-mac blend pots are really stereo volume controls with A taper on both sections, although they seem to work fine, when I checked them on a meter they did not read the same when in the middle detent.

EMG and Basslines seem to use linear taper pots, and they work well also.
 

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