Wiring Question - need help!! ( 3 way switch and blend knob)

[Mr123Clark]

Hello folks!

Just wiring up my first bass and came across this link detailing how to set up a 3 way switch with a blend knob in the middle position - I've tried it out using the specific MEC On/On/On 4PDT and while there is signal coming from the bass when in the middle position, it doesn't work like a traditional blend between the P and J pickups I have. Basically it seems almost like the first half before the detent is just the P and the second half turn is just the J but there's not really a good strong signal for the middle position.

I'm using a 250K ohm CTS balance/blend linear taper pot, with center detent - would this be the wrong sort of blend pot? Or is the wiring diagram just straight wrong

Thanks for the help!

 

[kgbeast]

Assuming the switch terminals are like this
01:02:03:04
05:06:07:08
09:10:11:12
Did you install jumpers 05-03 and 07-04 ?

 

[Mr123Clark]

Assuming the switch terminals are like this
01:02:03:04
05:06:07:08
09:10:11:12
Did you install jumpers 05-03 and 07-04 ?

yep! installed all the jumpers, but still getting my proper signal which makes me think its less a switch issue and more a blend pot issue - does that make sense? this is my first soldering guitar project

 

[kgbeast]

Then you must have miss wired the blend.
1:2:3
4:5:6
You have 3-ground, 6-signal
Try to do 3-signal, 6-ground.

 

[Mr123Clark]

no luck with switching the ground and signal - now I'm only getting my neck pickup

 

[kgbeast]

Does thim mean that the weak J signal is now gone?
If that is the case you need to check criss cross jumpers in the blend pot. With this connection of signal and ground, you should get either just neck adjustable or just bridge adjustable. See if you get that after fiddling with 3-4 jumper,

 

[kgbeast]

If you checking with multimeter, connect the multimeter to 4 and 2 or 3 and 5. In one case you should see 0 and in another 250k. Well if pickup is connected you will see few k instead of 250k on that position.

 

[Mr123Clark]

Have to leave for band practice but will check that later - what setting should i put the multimeter on?

 

[ctmullins]

What does the center position sound like? You may have the pickups out of phase. Are they from two different manufacturers?

 

[Mr123Clark]

ok rewired it up - i get sound left and right for the two pickups but nothing in middle position - tired reversing ground and output but then that gets NO signal

 

[fig]

Or is the wiring diagram just straight wrong

Yes, sir, it is. Wiring problems with the switch and the blend pot. I'll finish it up and show you tomorrow.

 

[Mr123Clark]

think I actually got the three way switch and blend to work after switching to a Alpha MN250k blend pot that I wired up in the traditional blend pot wiring. Although it definitely seems like there isn't much blending going on in the sweep basically the blend feels pretty close to a 3 way switch anyways - would this be because of the pot value or something else?

 

[ctmullins]

think I actually got the three way switch and blend to work after switching to a Alpha MN250k blend pot that I wired up in the traditional blend pot wiring. Although it definitely seems like there isn't much blending going on in the sweep basically the blend feels pretty close to a 3 way switch anyways - would this be because of the pot value or something else?

That's common for normal passive blends. You can try disconnecting the ground on the blend pot. That turns it into a variable series resistor instead of a shunt to ground, which will "stretch out" the sweep.

 

[fig]

think I actually got the three way switch and blend to work after switching to a Alpha MN250k blend pot that I wired up in the traditional blend pot wiring. Although it definitely seems like there isn't much blending going on in the sweep basically the blend feels pretty close to a 3 way switch...

Very cool you rewired the Blend pot to the common way.

As ctmullins just said, removing the ground connection from the Blend pot will probably improve the sweep so it isn't so ONsy/OFFsy. If you look up "ungrounded blend" in the forum, there's alot said and is regarded as an excellent improvement by most everyone who've done it.

Regarding the original diagram in first post, there were some issues. As you've discovered yourself, rewiring the Blend to the traditional way helped out.

Here's a diagram for folk still learning this stuff that shows the common numbering sequence of the Blend pot's terminal lugs (1 thru 6). The schematic shows how a Blend pot is electrically represented, the numbers match the lugs. The numbers 0 (off) and 10 (full volume) show the volume of each pickup, depending on wiper arm position. The sawtooth line is the resistance segment, the straight line is conduction segment of 0 ohms. Drawing shows Blend centered, full volume output (10) of both pickups to lugs 3 and 4.

Back to the original diagram, the Ground and Output of the Blend pot were reversed. Along with the mis-wiring of the switch, here's what would happen.
-Bridge Position - Neck pickup signal gets grounded (lug 3 of Blend pot), no output. Bridge pickup signal doesn't go to Blend pot, but stays full volume out of lug 'h' of switch.
-Middle Position - Neck and Bridge pickup signals both get grounded (lug 3 of Blend pot). No output.
-Neck Position - Neck pickup signal doesn't go to Blend pot, but stays full volume out of lug 'h' of switch. Bridge pickup signal gets grounded (lug 3 of Blend pot), no output.

About the switch and blend pot numbering and lettering. They help make wiring things easier and is the first thing I do to get oriented. It's also a common practice across all industries to use these 'reference designations'. You can label them anything you want. Numbers, letters, your favorite basses, your favorite fish or fowl (Switch lug trout connects to Blend lug eel). As long as you're consistent throughout your project, you're golden.

Anyhow, it seems you have the Blend pot sorted, now ya gotta sort out the switch wiring.

Hope this was useful.