Change in sound - can't really figure out why

[Notachemist]

Hahaha! Well played - at least you have a very good reason to save money on frequent string changes, then.

[edwardofhuncote]

🤔 Now that I think about it, if that sideways Q-switch is loose, this may actually be causing some of your issue. It could certainly cause some noise if the switch isn't making solid contact with the shielding paint.


Pop the hood on that MK and see if it's worked loose and may be touching something it shouldn't.

[keith_h]

When reading your post where you said when panned towards the neck the sound got nasaly and when panned towards the bridge it got boomy the first thing that came to mind is the pickups were connected backwards on the pan pot. It looks like you confirmed that. Since the connectors are not connected as I would expect them to be it might be worthwhile reseating all of the connectors in case someone was in there and caused the connectors to not be fully seated. A loose connector might be a cause of the issue you are seeing and is easily eliminated. 

[Notachemist]

Thanks for the suggestions. I will check up on the Q-switch and pan tomorrow. It has been mentioned that the Q-switch is tightened with a wrench at the nut, but how do you switch the pickup leads on the pan operator? Is it done by swapping two connectors (one for each pre-amp)? When I was switching the 9V battery, there were quite a lot of cables, so I would appreciate, to be 100% certain I'm not fiddling with the wrong cable(s).

[edwardofhuncote]

Thanks for the suggestions. I will check up on the Q-switch and pan tomorrow. It has been mentioned that the Q-switch is tightened with a wrench at the nut, but how do you switch the pickup leads on the pan operator? Is it done by swapping two connectors (one for each pre-amp)? When I was switching the 9V battery, there were quite a lot of cables, so I would appreciate, to be 100% certain I'm not fiddling with the wrong cable(s).

Yes, that simple. Should be a brown or possibly white modular connector for each pickup; just switch them where they are plugged-in. Don't flip them, as in the orientation of the plugs-to the pins they plug into, as this will flip the polarity. (ask me how I know...) Plug each pickup back in the same direction as before,  just on the opposite output.


If you can, post us a picture of your electronics cavity and we'll point you to this. Signature can be a little bit crowded in there, but it's just two wires, and they are coming from your pickup leads... easier to trace.

[JimmyJ]

Here are a couple pics of electronics I've borrowed from the Interweb.  I believe these are Signature packages of differing ages.  Arrows point to the pickup connectors which can be swapped between the two locations.  As edwardof... said, don't rotate these connectors - if these pics are right, the correct polarity leaves the white wire of the pickup cable visible at the connector when it's plugged into the circuit board.

BUT ... as you can also see by these two pics there is not much allowance for a Q-switch to rotate!  I'm gonna go out on a limb here and suggest that if you have a spun Q-switch, THAT is the cause of your change of sound.  I think you'll find either a lead to that switch is shorting to another terminal or you've lost one of the leads coming out of that capacitor (the small can between the board and the switch).

Open that puppy up and show us what you find!

Jimmy J

[Notachemist]

Is there any sort of indication on the connector, as to make sure I am not accidentially going to flip them, aside from the color of the wire on each pickup cable? If I recall correctly, it had one white housing and one brown housing on each connector.

I think it would be most wise for me, to proceed cautiously, and take a couple of photos of the electronics in the cavity, before I start tinkering. I do recognize the ferrite bead and what I assume to be both preamps from the photos that Jimmy posted, but although I am not sure if it is of any help, I will note that the bass sounded fine for almost half a year with the spun Q-switch, before it recently started to sound different. But I want to stress, that I really appreciate the input, that you guys are taking the time, to offer.

I will also add, that I have noticed a sort of hum, when the bass is plugged into the audio interface, which gets louder, the more i turn up the gain - the hum is pretty faint at full gain, but audible if you pay attention - I am not sure if this hum started at the same time, as the tone started to change, but it's possible. Turning the gain knob to 0 on the bass, makes the hum go away, and switching cables just makes the hum louder or quieter, depending on the quality of the cable. I have been doing a bit of reading online, and it seems that humming is decently common with USB audio interfaces, due to the many internal components in a pc, working and interferring at the same time as the audio interface, but in my experience, troubleshooting things like this, can be a real headache, so it's important to note that it sounded more "normal" through a bass amplifier. I wonder if this hum contributes to the "boomy" sound I am hearing, all of a sudden, since it is operating in the same area of frequencies, if that makes sense.

Anyways: Pictures coming up tomorrow, nevertheless.

[edwardofhuncote]

Is there any sort of indication on the connector, as to make sure I am not accidentially going to flip them, aside from the color of the wire on each pickup cable? If I recall correctly, it had one white housing and one brown housing on each connector.

I think it would be most wise for me, to proceed cautiously, and take a couple of photos of the electronics in the cavity, before I start tinkering. I do recognize the ferrite bead and what I assume to be both preamps from the photos that Jimmy posted, but although I am not sure if it is of any help, I will note that the bass sounded fine for almost half a year with the spun Q-switch, before it recently started to sound different. But I want to stress, that I really appreciate the input, that you guys are taking the time, to offer.

I will also add, that I have noticed a sort of hum, when the bass is plugged into the audio interface, which gets louder, the more i turn up the gain - the hum is pretty faint at full gain, but audible if you pay attention - I am not sure if this hum started at the same time, as the tone started to change, but it's possible. Turning the gain knob to 0 on the bass, makes the hum go away, and switching cables just makes the hum louder or quieter, depending on the quality of the cable. I have been doing a bit of reading online, and it seems that humming is decently common with USB audio interfaces, due to the many internal components in a pc, working and interferring at the same time as the audio interface, but in my experience, troubleshooting things like this, can be a real headache, so it's important to note that it sounded more "normal" through a bass amplifier. I wonder if this hum contributes to the "boomy" sound I am hearing, all of a sudden, since it is operating in the same area of frequencies, if that makes sense.

Anyways: Pictures coming up tomorrow, nevertheless.

Now we're getting somewhere. If you're getting a hum, this a a symptom that something is likely loose from the shielding, and it sounds like from what you're describing, the Q-switch is suspect. Humming, buzzing and sometimes crackling are often heard as the contact is intermittent.

Study on Jimmy J's borrowed pics there, and you should be able to trace your pickup leads down. The two wires looped through the ferrite bead should be the pickup leads.

To answer your other question (I've bolded it in the quote) yes, just study the modular plug. They are oriented to plug in a specific direction, but it is possible to reverse them. It's very easy to correct. Stay on target and keep us posted.

[mica]

Yes, there is a friction lock on the connectors. If you are really concerned you might put the connector on incorrectly, you can add a little mark with a pen so you know you have the right direction when you swap besides the locking mechanism in fact being locked.

IMPORTANT: do not pull on the wires when unplugging. Handle the plastic housing only. You may need to unmount the control to access the connectors, or use needle nose pliers. If you pull the wires, you can dislodge the crimp, and that can cause a host of issues from hum to signal loss.

Hum is a very specific frequency, in the US it's 60Hz. Are you certain you are hearing hum? Could it be a higher frequency?

Also, just how close to your PC are you? Does the noise you are hearing diminish when you get farther away?

One more time on pickup nomenclature:

• The bass pickup is neck pickup
• The treble pickup is the bridge pickup

For clear communication, I'd stick with using either bass/treble OR neck/bridge.

[BeenDown139]

dunno if this helps, here's a pic of my 2018 MKD cavity all lit up and everything 

[Notachemist]

https://imgur.com/a/jB8s0Bq

As promised, I have uploaded a few photos for you to take a look at. the spun Q-switch is the one in the top of the cavity, besides the 9V battery, if memory serves me right. I also noticed that the cavity has a piece of foam attached the non-visible side (the side that faces the electronics) - I assume that's normal.

Mica, the pen suggestion is great - thank you. So the friction lock means it's kept in place by a plastic lock, if you understand what I mean? Is it the type of connector where you have to "wiggle" them, or should it just slide off, when unlocked?

In regards to the hum: The best way I can describe the sound I faintly hear, is the sound you hear, when touching a surface with an instrument cable, that is connected to an amplifier, that's turned on, and it sounds like low frequency to my ears.

And I am sitting at around 80-90 centimeters (0.3937 inches) from my PC, and the noise stays the same if I move closer or further away from the PC. From now on, I will refer to the pickups as being neck and bridge pickups.

To everyone so far: Thank you very much for the continued help, and I hope these pictures can be of help.

[edwardofhuncote]

Okay, having looked at the pics... wow, that's a tangle. Seriously, it's not too bad. How handy are you? This isn't too bad, but you'll have be somewhat patient and tool-sy to do it.


If I were going to perform this operation, I'd -


1. Take a picture. (you already did)
2 .Take the battery out.
3. Unplug the pickup leads. (note which one is bridge and which is neck... good opportunity to mark them)
4. Lift the ferrite bead with leads and the battery wires out of the way so you can access the Q-switch.
5. Determine if it's loose. It's probably semi-tightened up in a slightly rotated position.
6. Put the bass in your lap so you can hold the switch with one hand. Loosen the 5/16" nut with the box end of a wrench. No need to take it off, just loosen a thread or two. Hold the switch while doing this. Do not let it twist the wire leads to it.
7. Gently turn the switch back to the direction it belongs with your fingers, and hold it in place while you snug the 5/16" nut. Just snug it, don't overtighten.
8. Switch those pickup leads to the opposite points of where they were in your picture so your pan function will be intuitively like you imagine from the player's perspective... L/R.
9. Ease the ferrite bead back in place. Usually that foam piece you mentioned lines up with it... keeps it in place and from clacking against the backplate.
10. Reinstall the battery. (I'd put a new one in, just because...)


11. Because it goes to eleven... Seal up the backplate and give it a run. Don't forget to give that amp a good bonk. 

[mica]

I've marked where the friction locks are with green circles in one of your images. It's really easy to see how it works with the one that is the original brown color and newer "natural" color. You can pull the connector straight out provided you are holding on the plastic housing only, but a little wiggle can be helpful to get it going.

We generally recommend being at least 1 meter away from an amplifier or computer, and you're close to that. When you say it doesn't change when you are closer or farther away, what kind of distance are we talking about? What about when you are twice the distance away?
The foam is to keep the ferrite bead from rattling.

For high frequency noise there is an upgrade where you replace the 8-pin ICs on the filter boards (and ideally the pan control as well) with a new tiny circuit card that has the IC and other components to take care of the high frequency noise filtering. None of this is what you are observing in your situation, but it's something that should be done at some point.

[Notachemist]

@Edward:
Oh no, it doesn't sound good when you describe it as being a tangle - the pictures were taken very close to the cavity, so maybe it looks more crowded, than it really is.
I would think of myself as being better at handling books than handling tools, if that makes sense . But really, in this specific case, I am usually not fond of tinkering with my Alembic, due to the fact that I live several thousand kilometers away from the factory itself, so any mistake made, is going to be costly and time-consuming to fix. As an example, Jimmy was very kind to assist me in adjusting the truss rods when I first got my Alembic (first time I ever encountered the dual truss rod system), but I am still not very comfortable adjusting them. I would say that I am so far comfortable doing pretty basic stuff like height adjustments and changing strings etc.

Swapping the pickup leads sounds manageable to me, but the Q-switch operation sounds more demanding, especially on my own, which is pretty unfortunate, as that is probably most likely to be the source of any unwanted noise, in relation to the instrument itself. I will say, that I spend 99.9% of my time playing with the pan centered, so unless it could be a possible cause for the change in sound, I would rather leave it alone.

@Mica:
I will try to double the distance, and see if anything improves. I tried using my backup bass (a Sandberg with active electronics ) with the same PC and Audio Interface, and I actually noticed that it was very noisy as well (more than the Alembic) - I even experienced noise changing just by hovering my hand over the tone controls, leading me to believe that all of this could be caused by either the PC or the audio interface - but I will try doubling the distance, and report back with my findings.

[Notachemist]

Well, I promised Mica an update on my findings when increasing the distance, and I think I have found the cause of the problem: The metal casing of my PC and worn strings.

I tried connecting the Audio Interface to a PC made of carbon fiber plastic, and pretty much all noise was gone immediately upon connecting both basses to the audio interface. Interestingly enough, the switch doesn't seem to cause any unwanted noise when connected to the other PC, so I think the switch still in contact with the silver in the cavity area @Edward.

So, if anyone reads this at some point in time, trying to figure out a sudden onset of noise while playing through a USB audio interface, try switching to a PC made of a materal that isn't conductive to noise, and change those strings!