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Blend knob mod for passive jazz

Cristo

Cristo

Jun 10, 2005
1,006
263
South Carolina, USA
#1
Who here has replaced the V-V-T config on a passive jazz with a V-B-T and deemed it a worthy mod?

I like the idea of one knob for volume and one for fine blending, but I'm hesitant to go through the trouble to discover that either it sucks or it's not much of a difference.

Also, I've read that some people experience a volume drop at the center position - although I notice a volume drop now when both Vs are on full anyway.
 
#4
Although it's not a J, and it has active EQ, I modded my fretless from VV(EQ), to VB(EQ). To match my five-string.

My reason was, when I play it at church I wanted to be able to kill the volume w/o losing the subtle blend between the pups. At church there's not an opportunity to 'test/noodle' to adjust the sound back after killing both v's.
So the mod made sense.

Since then, I've added a volume pedal to my pedal board. I've considered returning to the VV(EQ) set up because the variations are better with two volumes.
IMHO, YMMV, a different bass could react differently.
 
#5
I did this mod when I added the bridge pickup. For the style of music I'm playing, It was not all that useful. It's bennefit would be if you had to change from mostly neck pickup to mostly bridge. I my case, I never use more bridge then neck pickup. I think that kits for this setup are available through most parts dealers, If you decide to go that route.
 
#6
This is one of my favorite mods for a j-bass.

Here is a diagram I drew up if you haven't found a diagram already.

Cheers,

Andy

jbass_mod.gif
 
#11
I was in a guitar store one day playing around with a cool bass that had a magnetic pickup and a Piezo bridge. It also had a blend pot that allowed you to control the mix ratio of Piezo to magnet. It was a neat idea that worked well. So when I decided that I would add magnetic pickups to one of my guitars I thought what better way to mix them with the Mike Christian Piezo Bridge than with a blend pot? After hearing other builders sing the praises of the Blend Pot offered by instrument supplying Gods Stewart MacDonald I decided to give it a shot.

Blend Pot Closeup A quick trip to Stewart Mac turned up exactly what I was looking for. My order arrived 3 days later as usual. The pot is small which makes it easy to fit into your guitar but tricky to wire. Using the instructions on the Stew-Mac web site, I didn't have any trouble wiring it up to my two S-90 pickups but a novice might find it tricky because of the close quarters of the soldering lugs.

Once the pot was installed I tweaked it a little bit and loved the smooth action and the center detent. That's about where the love affair ended. As I rotated the knob from "Full Bridge" to "Center" to "Full Neck" I noticed three distinct sounds, bridge, center and neck. No interesting, subtle "in between " sounds were apparent to my ear. This passive blend device does nothing more than a 3-position switch would do. I'm sure there are interesting possibilities for this little trick if one were building a 2-channel pre amp or something like that. However, right out of the box it's is completely underwhelming and not worth the time or effort to install.
 
#12
Searcy said:
As I rotated the knob from "Full Bridge" to "Center" to "Full Neck" I noticed three distinct sounds, bridge, center and neck. No interesting, subtle "in between " sounds were apparent to my ear. This passive blend device does nothing more than a 3-position switch would do.
Click to expand...

That's interesting, and strange, because I was expecting a "blend" - a continuum of tones between the pickups, and not just one, the other, or both. Probably exactly what you were expecting!

Anyone else have that experience?

I just find the two volumes a little unwieldy, and only the first 10% or so of travel has any impact on the tone as far as I can tell.
 
#13
Cristo said:
That's interesting, and strange, because I was expecting a "blend" - a continuum of tones between the pickups, and not just one, the other, or both. Probably exactly what you were expecting!

Anyone else have that experience?

I just find the two volumes a little unwieldy, and only the first 10% or so of travel has any impact on the tone as far as I can tell.
Click to expand...

It sounds like maybe the wrong value of pot or taper was used. IME blend knobs kick separate volume knobs butts!

Or maybe too much ear wax?

:hiding:

:D

Joe.
 
#14
Vol - Blend - tone

1. Set the volume once
2. Work the blend to quickly nail the bass/mid sound you want for the song

If there is volume loss, which I have never noticed, what's the big deal? Set the volume to what's required.
 
#15
Searcy said:
I was in a guitar store one day playing around with a cool bass that had a magnetic pickup and a Piezo bridge. It also had a blend pot that allowed you to control the mix ratio of Piezo to magnet. It was a neat idea that worked well. So when I decided that I would add magnetic pickups to one of my guitars I thought what better way to mix them with the Mike Christian Piezo Bridge than with a blend pot? After hearing other builders sing the praises of the Blend Pot offered by instrument supplying Gods Stewart MacDonald I decided to give it a shot.

Blend Pot Closeup A quick trip to Stewart Mac turned up exactly what I was looking for. My order arrived 3 days later as usual. The pot is small which makes it easy to fit into your guitar but tricky to wire. Using the instructions on the Stew-Mac web site, I didn't have any trouble wiring it up to my two S-90 pickups but a novice might find it tricky because of the close quarters of the soldering lugs.

Once the pot was installed I tweaked it a little bit and loved the smooth action and the center detent. That's about where the love affair ended. As I rotated the knob from "Full Bridge" to "Center" to "Full Neck" I noticed three distinct sounds, bridge, center and neck. No interesting, subtle "in between " sounds were apparent to my ear. This passive blend device does nothing more than a 3-position switch would do. I'm sure there are interesting possibilities for this little trick if one were building a 2-channel pre amp or something like that. However, right out of the box it's is completely underwhelming and not worth the time or effort to install.
Click to expand...
I'm curious about why the pot is not blending - what value did you use - 250k or 500k? What value pot for the master volume? There is another way to wire up a blend pot that can be found on GuitarElectronics.com that doesn't ground the pickups but shunts the signal (+) of the pickup back to the neg. wire (shield) of that pup. I'm about to install a blend pot in my Yamaha fretless (now 2 pup,v-v-t) and not sure what path I want to take. I guess I may have to experiment and find out.
 
#16
I know this is an old thread, but I'm having exactly the same problem that Searcy described. I got a pre-wired control plate with a blend knob for my passive Jazz.

If I turn the blend knob from 5:00 (neck soloed) to 12:00 (both on full) to 7:00 (bridge soloed), it only really seems to do anything between about the 11:00 to 1:00 positions.

From 1:00 to 5:00, I seem to have a nice full neck sound. From 11:00 to 7:00, I have a nice full bridge sound. At 12:00, I have noticeably less volume and a really thin sound. The tone seems to change very smoothly but very rapidly as the knob goes from 11:00 to 1:00.

The pickups are SD SJB-1's if that info helps.

The control plate was pre-wired so I just had to solder the pickup hot leads (one white, one yellow) to the lugs on the blend pot, the pickup grounds (black) and the bridge ground wire I attached all to the ground lug on the output jack.

Can anybody shed some light on what is wrong?

Is there any specific test I can do to figure this out? It seems like maybe the problem is the blend knob taper is simply bad for use in this application and the resistance increases way too quickly or something.
 
#17
I just found this in a Blend Knob review on StewMac.com. Might this be my problem?

if the DC resistance value (k ohms) of your pickups is different the center detent position will have less volume than to just either side of the detent position. So.... as you are smoothly blending from the one pickup to the other there will be a very unpleasant drop in volume at the center detent position which is suppose to be full on for both pickups.
Click to expand...
 
#20
I wouldn't go so far as to say a Jazz with 2 volumes is unusable for me, but it sure isn't user friendly. I have 2 Jazzes that I gig frequently and both have the VBT setup, along with hum canceling pickups.

That combination gives me all the tonal variety we love in a Jazz, but I can also fade in and out of tunes, turn the bass off between songs without messing with my blend, and easily adjust my level mid-song.

I do hear a VERY slight drop in volume with both pickups on full, but the same is true with every VVT bass I've tried. I almost never run the bass that way anyhow so it's a non-issue.

For anyone keeping score my pickups are DiMarzio Ultra-Jazz and DiMarzio Area J's, both with 500K pots so I get all the highs the pickups are capable of.
 

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