Blend pot difficulty

[cvanscott]

I have a 5 string jazz bass I am running with an Aguilar obp-3 preamp. the Pickups are both duncan basslines, an active single coil in the neck and a music man replacement in the bridge.

My problem is this: both pickups work if you turn the blend knob to either end (either all neck or all bridge). when you turn the know towards center, the volume decreases and when it sets into the center detent, there is no output at all.

Ideas?

 

[walterw]

i'd suspect a "mirror image" blend pot, where the connections are reversed.

 

[jondog]

I have the same problem. What is the proper way to wire a mirror image blend pot?

 

[walterw]

exactly "mirror image" of how it's wired now.

 

[cvanscott]

exactly "mirror image" of how it's wired now.

Do I have to reverse everything as in left to right or row 1 to row 2? Or do i just swap the output and the lead to the volume pot?
Thanks for the reply!

 

[SGD Lutherie]

Do you have a multimeter? If you do, put the pot at the center position, and then check from the outsides to center lug on each deck.

You should get readings something like this:

This was the readings for a 500k Bourns M/N taper blend pot. Other M/N blends should be similar. Some pots are reverse from this, so a meter is a handy thing to have. You can get a cheap one at RadioShack that will do the job.

You can see that when the pot is at the center detent, one side is close to zero, and the other is close to the pots full value.

You want the low resistance side to go to hot, and the high resistance side to go to ground.

 

[cvanscott]

Do you have a multimeter? If you do, put the pot at the center position, and then check from the outsides to center lug on each deck.

You should get readings something like this:

This was the readings for a 500k Bourns M/N taper blend pot. Other M/N blends should be similar. Some pots are reverse from this, so a meter is a handy thing to have. You can get a cheap one at RadioShack that will do the job.

You can see that when the pot is at the center detent, one side is close to zero, and the other is close to the pots full value.

You want the low resistance side to go to hot, and the high resistance side to go to ground.

Thanks for the reply!

Now I'm just trying to understand this, but if I am dealing with a mirror image pot, which I believe I am, wouldn't it stand to reason that the hot wire from both pickups would stay on the center lugs, and everything else would get switched? Maybe I'm wrong but that's what it sounds like to me.

I do have a multi meter so I will check out what is going on before I do anything.

 

[SGD Lutherie]

Thanks for the reply!

Now I'm just trying to understand this, but if I am dealing with a mirror image pot, which I believe I am, wouldn't it stand to reason that the hot wire from both pickups would stay on the center lugs, and everything else would get switched? Maybe I'm wrong but that's what it sounds like to me.

I do have a multi meter so I will check out what is going on before I do anything.

If the pot has both decks going in the same direction, then it's not a blend pot, and will never work correctly. Get a proper blend control and don't waste your time with that.

Check each side with the multimeter with the pot at the center detent and see what you have.

Most likely it's just wired up backwards, i.e., hots and grounds swapped.

 

[ChrisPbass]

I have a similar issue. I get 100% when rolled either way but at center detent output is at 40% maybe.

/end highjack.

 

[cvanscott]

If the pot has both decks going in the same direction, then it's not a blend pot, and will never work correctly. Get a proper blend control and don't waste your time with that.

Check each side with the multimeter with the pot at the center detent and see what you have.

Most likely it's just wired up backwards, i.e., hots and grounds swapped.

now when you say hots and grounds swapped, do you mean the hot wire coming from the pickup isn't actually the hot wire? thanks again!

 

[SGD Lutherie]

now when you say hots and grounds swapped, do you mean the hot wire coming from the pickup isn't actually the hot wire? thanks again!

No, I mean the connection from the blend pot to ground and the master volume. See my illustration above.

If you take a reading and see that the lug you have going to ground reads close to zero between it and the center lug (2.8Ω in my example above), than that needs to be switched as the output. If that remains as ground, it will reduce the output of the pickup in the center instead of having it at full volume.

The (+) wire from the pickup always connects to the wiper (center lug) as shown as Source A and B.

 

[jorri156]

sounds like things are out of phase if you ask me, especially if its a thin sound. another almost certain problem if its a volume loss could be that you aare using a dual gang pot which is linear or logarithmic. this means you get the effect of two volume controls on 50%.

if you want more of an 80/80 split, then you need a log/antilog dual pot. these can be made using a resistor of about a third of the pot resistance, this is put in parallel with the part of the pot that's not to ground (i.e. the 'in' and 'out' pins). you can use a bigger pot to compensate for the reduction made by the resistors.

you need a linear pot for this. a log pot would really screw things up.

see here: Link Removed

another problem is wiring like a volume control as this creates paths to ground on some settings and you need to ensure the in and out are swapped like in the diagram.

 

[SGD Lutherie]

I just reread the first post... the problem is you can't mix active and passive pickups. The active neck pickup is loading down the passive pickup.

So you either need an active bridge pickup, or you need to run it through a preamp to make it active.

 

[cvanscott]

I just reread the first post... the problem is you can't mix active and passive pickups. The active neck pickup is loading down the passive pickup.

So you either need an active bridge pickup, or you need to run it through a preamp to make it active.

I see it is confusing the way I worded the first post. I am running both pickups with an Aguilar OBP-3 preamp, so both pickups are active.

 

[SGD Lutherie]

I am running both pickups with an Aguilar OBP-3 preamp, so both pickups are active.

No, they are not. The active pickup has a low impedance output, and the passive one has a high impedance output. The active pickup is loading down the passive pickup, regardless of the Aguilar after them. It's still a passive pickup connected to a preamp.

This is evident by the problem you are having.

To make them both active you would need to insert an addition preamp between the passive pickup and the Aguilar.

 

[cvanscott]

No, they are not. The active pickup has a low impedance output, and the passive one has a high impedance output. The active pickup is loading down the passive pickup, regardless of the Aguilar after them. It's still a passive pickup connected to a preamp.

This is evident by the problem you are having.

To make them both active you would need to insert an addition preamp between the passive pickup and the Aguilar.

Well now that changes everything. I guess I am now questioning exactly what pickups I have then. I'll need to pull the neck pickup to identify whether it is active or not, but Seymour Duncan's website tells me that the humbucker I have in the bridge is a high output pickup, but does that mean it is an active pickup? I'm sorry for my stupidity. I'm obviously not very well versed on electronics, or so I am finding out!

 

[SGD Lutherie]

Well now that changes everything. I guess I am now questioning exactly what pickups I have then. I'll need to pull the neck pickup to identify whether it is active or not, but Seymour Duncan's website tells me that the humbucker I have in the bridge is a high output pickup, but does that mean it is an active pickup? I'm sorry for my stupidity. I'm obviously not very well versed on electronics, or so I am finding out!

"Active" implies that there is a powered circuit in the pickup. Passive is a pickup that uses no power. Active pickups like EMGs and some of the Basslines have preamps built inside the pickup.

If your pickups have red wires going to the battery, then they are active.

 

[cvanscott]

"Active" implies that there is a powered circuit in the pickup. Passive is a pickup that uses no power. Active pickups like EMGs and some of the Basslines have preamps built inside the pickup.

If your pickups have red wires going to the battery, then they are active.

It turns out that both of my pickups are indeed active. I checked the blend pot with my multi meter and it was mirror image of the schematic you provided. I switched the hot and ground wires and it works great! Thanks for all the help!

 

[SGD Lutherie]

It turns out that both of my pickups are indeed active. I checked the blend pot with my multi meter and it was mirror image of the schematic you provided. I switched the hot and ground wires and it works great! Thanks for all the help!

Glad it worked out for you! They should be a standard layout, but they're not, so it's necessary to check them out with a meter to see which way they are laid out.