I want to add a passive tone control w the OBP-3

[Clark Dark]

I have several questions for the forum's electronics gurus.
I have two basses, a 4 string with an OBP-1 and a 5 string with an OBP-3. Both have 2 volume pots.
#1, I would like to add a passive tone control to each of them so could someone draw a diagram or share a link.
#2, In both basses I have Barts, P-J's. I am using 250K pots and here's where I'm fuzzy. I'm thinking the wiring I'm using has the pup's in parallel because the output of the neck pup is soldered to the output of the bridge pup and under the laws of parallel resistance that would be 125K into the inputs of the Aguilars. Please correct me if I'm wrong.
When I turn both volumes full on I lose some volume until I back off the bridge ( J pup ) then I get a fuller output from both basses. Need I change the vol. pots to 500K ?

[line6man]

Take a look at the PDF on the Aguilar website...
It shows a diagram of how to add the passive tone. It's a very straightforward mod.

[SGD Lutherie]

Originally Posted by Clark Dark

I am using 250K pots and here's where I'm fuzzy. I'm thinking the wiring I'm using has the pup's in parallel because the output of the neck pup is soldered to the output of the bridge pup and under the laws of parallel resistance that would be 125K into the inputs of the Aguilars. Please correct me if I'm wrong.

That's correct, and that's the way every passive bass with two or more pots is, and one of the reasons why a preamp opens up the top end.

The preamp is presenting a high impedance load, so it doesn't care, but the pots are loading down the pickups. You get more of a load when you turn the pots down a bit.

500K pots would help if that bothers you.

As line6man said, just follow the instructions for the passive tone control.

[Clark Dark]

SGD,
would changing to 500K's react differently when I turn both pup's full on ? I mean would I need to back off the bridge pup in order to achieve full volume ? Is there an alternate wiring for a P-J set up where you can turn both pup's on full and not have a choking of the output ?..not to be redundant but
Bartolini says to use 250K pots with these pup's but you're suggesting that I can go 500K and not lose much output from the pup's ?...or will there be a difference ?


line6man,
thanks for the tip, I didn't see the passive tone on the OBP-3 pg. so does that mean I can use the mod for the bass with the OBP-1 but not the other with the OBP-3 ?

[line6man]

Originally Posted by Clark Dark

SGD,
line6man,
thanks for the tip, I didn't see the passive tone on the OBP-3 pg. so does that mean I can use the mod for the bass with the OBP-1 but not the other with the OBP-3 ?

You can use a passive tone control with just about any set of passive pickups.

The tone control loads against the pickups, not the preamp.
The preamp could care less what happens before it's input.

[Clark Dark]

line6man,
on the site re: the OBP-3 it shows a dual 500K pot for variable midrange where you would think it would be a dual 50K pot...I try calling Aguilar but they're lacking in the customer service dept. Do you think it's a typo ?

[line6man]

Originally Posted by Clark Dark

line6man,
on the site re: the OBP-3 it shows a dual 500K pot for variable midrange where you would think it would be a dual 50K pot...I try calling Aguilar but they're lacking in the customer service dept. Do you think it's a typo ?

I don't know. That is something that is dependent on the way they designed the preamp to work, it isn't like a passive system where you can use whatever values you want to get the tone you want.

That diagram has been around for a while now, I doubt that it would be incorrect, but you should call and ask them if you are worried about this.

[Clark Dark]

okay I just got thru. I was told it is a 500K.
since I have 4 control holes in my 5 string body what I'm going to do is this...use a stacked control for my volumes, add a passive tone control (w a hovland musicap) keep the active mid and stacked bass/treble controls but where the toggle is placed I need to find a mini 500K pot for the variable mid sweep. Any idea where a dual concentric mini 500K A pot can be purchased ?

[fishsticks]

check out this thread:

either tone knob controls both pickups

and then this one:

http://www.talkbass.com/forum/showth...t=#post7883431

[fishsticks]

Originally Posted by Clark Dark

okay I just got thru. I was told it is a 500K.
since I have 4 control holes in my 5 string body what I'm going to do is this...use a stacked control for my volumes, add a passive tone control (w a hovland musicap) keep the active mid and stacked bass/treble controls but where the toggle is placed I need to find a mini 500K pot for the variable mid sweep. Any idea where a dual concentric mini 500K A pot can be purchased ?

http://www.guitarpartsresource.com/e...l_minipots.htm

i think you can buy one here, but the picture says 250k.... so i'm not sure

[line6man]

Originally Posted by Clark Dark

Any idea where a dual concentric mini 500K A pot can be purchased ?

No, but the diagram called for a linear taper, which is B500K.

[Clark Dark]

I appreciate everyones input. I now have the template for what I'm going to do. Thanks for the link for series parallel wiring and I have a message into GPR (and they do have mini dual 500K just doesn't say whether it's linear or audio). I even found out that generally log is equal to audio as far as the taper and understand the sweep of linear pots more acurately.

[SGD Lutherie]

Originally Posted by Clark Dark

I appreciate everyones input. I now have the template for what I'm going to do. Thanks for the link for series parallel wiring and I have a message into GPR (and they do have mini dual 500K just doesn't say whether it's linear or audio). I even found out that generally log is equal to audio as far as the taper and understand the sweep of linear pots more acurately.

Log is the same as audio. But you want linear for active tone controls so that you have an even frequency sweep.

With a linear taper, turning the pot half way gives you 250K. That's not true with a log taper, where 50% of the rotation might give you something like 10 or 80% of the resistance.

[Clark Dark]

okay if I wire the P-J with a push/pull for series and parallel I can defeat the loss of volume when both pup's are on 10, although it will for all purposes turn the pup's into one big humbucker. ..question, isn't the P pup because it's two single coils basically a humbucker ? I mean isn't the pup itself wired in parallel ? I ask because if this is correct then I could use a 500K on the P and a 250K on the J, in theory.

[line6man]

Originally Posted by Clark Dark

okay if I wire the P-J with a push/pull for series and parallel I can defeat the loss of volume when both pup's are on 10, although it will for all purposes turn the pup's into one big humbucker. ..question, isn't the P pup because it's two single coils basically a humbucker ? I mean isn't the pup itself wired in parallel ? I ask because if this is correct then I could use a 500K on the P and a 250K on the J, in theory.

250K versus 500K has absolutely nothing to do with whether you are using single coils or humbuckers.
You can choose either value depending on how much output and treble you want.

The coils of a P bass pickup are traditionally wired in series, not parallel.

[Clark Dark]

from wikipedia on the P bass:
Pickup(s) One single-coil (1951 — 1957);
One split pickup, pieces connected in humbucking mode (1957 — present);
One split "P" pickup and one eight-pole "J" pickup (2 magnets per string) connected in humbucking mode (some later models);
One split pickup and one humbucker (some later models).
I've worked on a lot of Gibson and Epiphone guitars and noticed that as a rule a humbucker had a 500K pot (sometimes with Gibson 330K). Stew Mac suggests using 500K with humbuckers also so please understand that I'm asking alot of questions here because I'm trying to cultivate some new ideas.

so a 500K pot allows more hi pass while the 250K pot allows more output. now I understand why the old concentric control J basses had a 250K on top of a 500K

[line6man]

Originally Posted by Clark Dark

from wikipedia on the P bass:
Pickup(s) One single-coil (1951 — 1957);
One split pickup, pieces connected in humbucking mode (1957 — present);
One split "P" pickup and one eight-pole "J" pickup (2 magnets per string) connected in humbucking mode (some later models);
One split pickup and one humbucker (some later models).
I've worked on a lot of Gibson and Epiphone guitars and noticed that as a rule a humbucker had a 500K pot (sometimes with Gibson 330K). Stew Mac suggests using 500K with humbuckers also so please understand that I'm asking alot of questions here because I'm trying to cultivate some new ideas.

so a 500K pot allows more hi pass while the 250K pot allows more output. now I understand why the old concentric control J basses had a 250K on top of a 500K

It is common practice that single coils are quite bright, so the highs are tamed out with 250K pots.
Humbuckers on the other hand don't have as much highs, so you retain their high end a bit with 500Ks.

You can use either value depending on what you want.
Keep in mind that Jazz and P basses both use the same value, and a Jazz has singles while a P has a humbucker. (250K btw)

No, 500K gives more output AND more highs.

These two threads may be helpful:
What effect does 1 meg pot have? Also, audio vs. linear
Passive basses and the volume control, an explanation (science warning)

[Clark Dark]

well I have 250K's in both basses now so I 'm going to try the 500K's along with the other changes we spoke about. Once again I thank you all for the info shared. I will post back as soon as I'm done.