Help troubleshooting Jazz bass

[byacey]

Your bass hummed before you shielded it - and exhibits the directional characteristics we expect. That means it's not cancelling electromagnetic fields - the RWRP situation that should exist between the 2 pickups doesn't.

You shielded it. Shielding helps with electrostatic fields (they're not the same thing). No amount of copper or paint shielding will ever help with electromagnetic fields - you need hum cancelling pickups to do that, and ...we established earlier on that you don't have hum cancelling pickups. So, your bass reacts the same to electromagnetic hum fields - that is to be expected.

Either one of your pickups is reverse wired, or the pair you have is not RWRP with respect to one another. Shielding is not your problem - the way your pickups are wired is. Whether the pickups are at fault, or the wiring in the bass is at fault is yet to be determined.

I agree completely, except it should be hum free if one of the pickups is reversed, even if the magnetic polarity is wrong. That would affect the sound of the bass, but common mode rejection will still work.
This is why I believe the pickups are mismatched as far as inductance and resistance.

 

[skycruiser]

Your bass hummed before you shielded it - and exhibits the directional characteristics we expect. That means it's not cancelling electromagnetic fields - the RWRP situation that should exist between the 2 pickups doesn't.

You shielded it. Shielding helps with electrostatic fields (they're not the same thing). No amount of copper or paint shielding will ever help with electromagnetic fields - you need hum cancelling pickups to do that, and ...we established earlier on that you don't have hum cancelling pickups. So, your bass reacts the same to electromagnetic hum fields - that is to be expected.

Either one of your pickups is reverse wired, or the pair you have is not RWRP with respect to one another. Shielding is not your problem - the way your pickups are wired is. Whether the pickups are at fault, or the wiring in the bass is at fault is yet to be determined.

Thanks, I appreciate the input. But I'm not sure it accounts for all of the checks I have done.

#1. I reversed the bridge pickup and found that it exhibits the "thin" sound when both are fully on, which typically would indicate pickups that are not reverse-wound. (Most of the sound cancels out). I also checked and confirmed that the magnet polarity on the two pickups are in opposite directions. Seems likely that these are in fact RWRP.

#2. I swapped in a set of pickups that are dead silent when fully on in another J bass. They exhibit the same noise imbalance.

#3. I completely took the pots etc. out of the circuit by disconnecting everything from the output jack. I then connected each pickup to the output jack one at a time and confirmed that they exhibit the imbalanced noise characteristics.

So what I think this leads to is that even with known and verified sets of RWRP pickups in this bass, they exhibit a major noise imbalance that appears to be unrelated to wiring in the control cavity. As far as I can tell, it is dependent on mounting position in the bass. Unfortunately they are not the same size pickups, so I can't swap them, but two sets exhibit the same issue.

 

[skycruiser]

I agree completely, except it should be hum free if one of the pickups is reversed, even if the magnetic polarity is wrong. That would affect the sound of the bass, but common mode rejection will still work.
This is why I believe the pickups are mismatched as far as inductance and resistance.

I think what I need to do is move the new pickups into the old bass and see if they are noisy in that bass. Unfortunately I took the electronics completely apart in that bass.

The one set being mismatched does not explain why a different set of pickups from another bass are noisy in the new bass. Seems to indicate it is not a problem with pickups.

 

[byacey]

I think what I need to do is move the new pickups into the old bass and see if they are noisy in that bass. Unfortunately I took the electronics completely apart in that bass.

The one set being mismatched does not explain why a different set of pickups from another bass are noisy in the new bass. Seems to indicate it is not a problem with pickups.

There really isn't anything left, except the output jack. You said you bypassed everything else.

 

[BassCajon]

Thanks for the advice. I'm using a fairly high-end soldering iron, Hakko 939. I actually have quite a lot of experience soldering, wiring and building electronics, having done professional electrical engineering work for over 2 decades as well as going through professional solder and inspection training more than once. That may why I am so annoyed with the whole idea of soldering to the back of a potentiometer. It is not something I would ever include in an electrical design. I think it is a horrible way to do a ground electrical connection, and is only done because at the point of first assembly, can be done without any major issues. Try reworking a few times or applying heat repeatedly and you will see that the entire pot can get very hot, and this is just getting it up to the point that the solder will melt. No matter how you slice it, you have to dump a sh!tload of heat into the metal casing to properly melt solder to it and make a solid connection.

What I believe is going on with the pots is that I spent too much time on the leads with the iron wicking off excess solder. I like to clean up a terminal before putting the wire back on. And now I have done this repeatedly with these pots, going back and forth with various tests. Most likely the heat damaged the metallic element (maybe a small PCB trace or copper foil) connecting the terminal to the inner parts of the pot. It works when hot but cools and shrinks, disconnecting the contact. Just speculation but I can assure you, from inspection, the wires are soldered well to the terminals. I have looked at thousands of solder joints in the last couple of decades and know what cold solder joints, disturbed joints and a wide range of other defects look like. I'm not having issues connecting wires to terminals.

Having said all that - this does not address my real problem at all...

It sounds like you have alot of electronics training which is awesome but i questioned your guitar testing and soldering methods based on what you're saying about the overheating of the pots and the unstable final connections. I also understand that you do a final inspect on the connections. You can see why i may have gone in that direction.

Regarding your issue soldering directly to the pot casing,
You can also put a small neat puddle of solder to the side top corner of the pot. Please watch that video i posted above. Watch how he grounds all of them by drawing little circles with the iron tip. This works very, very well, transferring minimal heat and it should only take a few seconds.

I guess the pots could be internally compromised from all of the heating but its also a Squier j bass. Does yours have the small pots? I understand you want to fix the issue but just upgrade to CTS or Bourns pots if they are as at the end of their line as you say. If anything it'll knock that one thing out of the equation.

 

[skycruiser]

It sounds like you have alot of electronics training which is awesome but i questioned your guitar testing and soldering methods based on what you're saying about the overheating of the pots and the unstable final connections. I also understand that you do a final inspect on the connections. You can see why i may have gone in that direction.

Regarding your issue soldering directly to the pot casing,
You can also put a small neat puddle of solder to the side top corner of the pot. Please watch that video i posted above. Watch how he grounds all of them by drawing little circles with the iron tip. This works very, very well, transferring minimal heat and it should only take a few seconds.

I guess the pots could be internally compromised from all of the heating but its also a Squier j bass. Does yours have the small pots? I understand you want to fix the issue but just upgrade to CTS or Bourns pots if they are as at the end of their line as you say. If anything it'll knock that one thing out of the equation.

Yes this is true, my work on guitars is fairly minimal. I have done a few pot swaps and pickup swaps, but this isn't something I do on a daily basis or anything close to it. I'm learning special techniques needed to work on these things, including cutting back on the heating time and not wasting heat cycles wicking off the excess solder.

These are the mini-pots which I actually like since it reduces the heat needed to solder to the casing. But I think the also have less thermal isolation between the solder terminals and internal sensitive elements which I seem to be overheating. I do plan to swap these pots for higher quality ones (and minimize the rework as much as possible).

For those still following along and offering advice (which I really appreciate!) please take a look at this video. I replaced the bridge pickup pot with one from the other bass so the intermittent issue is resolved for the moment. What you see here is the sensitivity of the noise to the location of the aluminum plate/pickguard. First I turn on the Neck pickup with the plate in place. This is the minimal noise scenario. When I remove it, the noise increases quite a bit. This is Neck Pickup Solo. I put the plate back and turn off the neck PU. Then I turn on the Bridge Pickup. You can hear the very loud noise. I then move the pickguard over to the location of the bridge pickup and the noise is cut back quite a bit, and varies as I move the plate around.

Something else to note: aluminum foil is not effective at reducing the noise. It is surprising to me but only the thick plate causes a noticeable reduction as shown in the video. There might a slight reduction with foil but nothing like what you hear with the pickguard.



Soooo..... Do I need to have a custom, full body aluminum pickguard installed on this bass???

I think it is possible that the main difference between this bass and my other one (now completely disassembled) is the extremely low noise level of the Neck pickup. This is great, but unfortunate that the bridge PU isn't equally low noise. This is my first experience with an aluminum pickguard. Maybe I should just replace it with a Tort guard and keep the PUs at 100% all the time. Though I really love the idea of a quite J bass with solo single coils. Just not sure how to get there...

 

[byacey]

Both volume controls should be the same resistance for it to balance properly. I still think the pickups are an issue because you said rhe dc resistance is different between the two.

 

[skycruiser]

Both volume controls should be the same resistance for it to balance properly. I still think the pickups are an issue because you said rhe dc resistance is different between the two.

Check out these specs from Fender. They sell matched sets with different dcr specs. This is very common.

Invalid Link Removed

 

[byacey]

Did you try connecting BOTH pickups directly to the output jack? And then flip the phase on one of them to see if the noise goes up, or down?
If you do this and still can't eliminate the hum, I still say it's a bad pickup(s).

 

[byacey]

Here is a thread about exactly the problem you're experiencing:Jazz bass pickups that don't cancel hum when used together
in particular, pay attention to post #16.

 

[skycruiser]

Here is a thread about exactly the problem you're experiencing:Jazz bass pickups that don't cancel hum when used together
in particular, pay attention to post #16.

Thanks. I understand RWRP and think I have done checks to confirm they are RWRP. And I will state again, I put in a different set of pickups that were fine in the other bass and they had the same problem in this one. The video I posted shows the noise is sensitive to shielding, which I dictates to me a shielding imbalance. @micguy doubted that but the video is pretty strong evidence.

 

[all_your_bass]

Have you tried wiring both pickups directly to the jack together? If I didn't miss something, it sounds like all of your tests with both pickups included (possibly defective) pots in the circuit. If there's something wrong with the rest of the electronics, this could explain your results with both sets of pickups.

 

[micguy]

Thanks. I understand RWRP and think I have done checks to confirm they are RWRP. And I will state again, I put in a different set of pickups that were fine in the other bass and they had the same problem in this one. The video I posted shows the noise is sensitive to shielding, which I dictates to me a shielding imbalance. @micguy doubted that but the video is pretty strong evidence.

Your description in your original post says the noise is direction sensitive. That says electromagnetic hum. Shielding isn’t the fix for that, rwrp is.

 

[byacey]

Thanks. I understand RWRP and think I have done checks to confirm they are RWRP. And I will state again, I put in a different set of pickups that were fine in the other bass and they had the same problem in this one. The video I posted shows the noise is sensitive to shielding, which I dictates to me a shielding imbalance. @micguy doubted that but the video is pretty strong evidence.

If the pickups are nulling the hum ie. in a balanced common mode state, the shielding will be nearly irrelevant.

 

[byacey]

Have you tried wiring both pickups directly to the jack together? If I didn't miss something, it sounds like all of your tests with both pickups included (possibly defective) pots in the circuit. If there's something wrong with the rest of the electronics, this could explain your results with both sets of pickups.

The OP mentioned in one of his posts that he did connect a pickup directly to the output jack, but it wasn't really clear if both pickups were connected simultaneously. In doing this test, all the other controls should be disconnected completely from the jack.

I still suggest a very telling test would be to disconnect the pickups completely, and solder a 50 or 100K resistor in place of the pickups, and then see what the noise situation is. This test will confirm or rule out "hum generating" controls, internal wiring, and the electrostatic shielding.

 

[skycruiser]

If the pickups are nulling the hum ie. in a balanced common mode state, the shielding will be nearly irrelevant.

Only if they produce the same hum characteristics. Clearly in this case they don't, so they don't cancel.

 

[skycruiser]

The OP mentioned in one of his posts that he did connect a pickup directly to the output jack, but it wasn't really clear if both pickups were connected simultaneously. In doing this test, all the other controls should be disconnected completely from the jack.

I still suggest a very telling test would be to disconnect the pickups completely, and solder a 50 or 100K resistor in place of the pickups, and then see what the noise situation is. This test will confirm or rule out "hum generating" controls, internal wiring, and the electrostatic shielding.

I connected each one separately to the out jack, nothing else connected. They each had the same noise as when fully connected and set to solo fully on.

 

[byacey]

Only if they produce the same hum characteristics. Clearly in this case they don't, so they don't cancel.

This answers your own question. Either you have a defective or wrong type pickup causing the mismatch.

 

[byacey]

I connected each one separately to the out jack, nothing else connected. They each had the same noise as when fully connected and set to solo fully on.

You need to connect them both at the same time to evaluate if they can actually cancel the hum. If it's still noisy, flip the phase on one pickup and compare. If it's still noisy, you have a definite mismatched / defective pickup.

 

[skycruiser]

Your description in your original post says the noise is direction sensitive. That says electromagnetic hum. Shielding isn’t the fix for that, rwrp is.

You may need to question this conventional wisdom. Please see the video below. It show the Neck pickup Solo. It is faint but there is variation in the noise as I move the bass with the pickguard (shield) on. When I take it off, the noise is much louder and you can hear the sensitivity to direction more clearly. Maybe "hum" is not the right word, but I have been saying throughout this thread there is a noise problem I want to resolve. It is very clearly direction sensitive and can be affected by shielding. (I suspect if I had a standard plastic, non shielded pickguard, I would hear the high noise level without the PG with the neck pickup solo.)

It is not clear to me why there are still questions about RWRP. I tested polarity with a magnet. I swapped the leads on one and got the characteristic thin sound of mis-matched pickups. And finally, I installed a completely different set of pickups that were silent in another bass (when both fully on) and they exhibit the same imbalance in this bass.

It seems clear to me that the problem is that they are picking up different noise profiles because they have different level of shielding. The previous video I posted and this one provide solid evidence of this right? What am I missing?

I am trying as hard as I can to understand the comments and do things that provide useful evidence.