Why is my bridge pickup buzzy but my ... Log Out | Topics | Search
Moderators | Register | Edit Profile

Alembic Club » Owning an Alembic » Troubleshooting » Archive through March 08, 2009 » Why is my bridge pickup buzzy but my neck pickup quiet? « Previous Next »

Author Message
Senior Member
Username: kungfusheriff

Post Number: 767
Registered: 8-2003
Posted on Thursday, December 04, 2008 - 1:14 pm:   Edit Post

I'm the proud owner of three Series 2 basses, and two of them have this noise problem: one of my '82s and my '95 have bridge pickups that buzz like crazy no matter how I adjust the humcanceller trim pot for that pickup. The other '82, however, is silent as are the neck pickups of the other two basses. None of the three has had the noise reduction upgrade as far as I can tell.
None of them have the internal gain controls cranked. The power is my house is on the dirty side, and the noise is the same whether I plug into a grounded or ungrounded outlet.
Any ideas, or is a little buzz going to be the price I pay to have this tone?
Username: mica

Post Number: 5715
Registered: 6-2000
Posted on Thursday, December 04, 2008 - 1:33 pm:   Edit Post

First - can you give a little more description of the "buzz?" High frequency, low frequency, directional, changes with filter control rotation?

Then you need to figure out where the "buzz" is originating. Test with 1/4" outs and the power supply. If you have 2 power supplies and cables, check with both to make sure one of them isn't the source.

Then you can swap the connections for the bass and treble pickups to see if the sound is from the pickups or in the preamp somewhere. You might have some problem that is not related to needing the upgrade, ICs and FETs fail, people are mean to wires over time, stuff happens.

One thing to be confident of, you do not have to settle for buzz to have the tone. You might have to have an upgrade to eliminate it.

Let me know how the troubleshooting goes.
Senior Member
Username: kungfusheriff

Post Number: 768
Registered: 8-2003
Posted on Friday, December 05, 2008 - 9:33 am:   Edit Post

I have two blue-box power supplies (1982 vintage) and three cables (two from '82, the third a new old stock unit bought recently on eBay) and the noise does not vary if I change which of these I am using. The buzz is in the higher frequencies and is directional, and also varies depending on where I stand in the room relative to electric light sources. Filter rotation does not appear to affect the buzz other than by rolling off the range of frequencies that contains the errant noise.

I have poked (gently) at the guts of all three basses and found no unusual deterioration, modification, fried components or signs of abuse. I do know that the '95 was dropped in its flight case while on its way to me, and that may be the reason the Molex connector that attaches the lead from the humcanceller to the circuit board is wobbly. But I think the Molex is intact enough to make a solid connection, and wrote this off the first time I troubleshot this noise problem.

The '82 was left to slumber in its case for about 10 years until I got it, and has some mild corrosion issues -- I don't know if you remember, but this is the bass with the sticky, grinding tone pots that makes "whoop" noises with the filters engaged. We discussed it over the phone sometime last summer. I don't get the impression that funky pots would cause hum in the bridge pickup only, but maybe I'm wrong.

Time permitting, I will swap the pickup leads on both basses today and report back. The noise is distressing but not worth losing sleep over, at least until the next studio project is at hand, whenever that is. Please feel free to place this problem well down on your list of priorities, and thank you as always for the guidance.
Intermediate Member
Username: lmiwa

Post Number: 123
Registered: 2-2008
Posted on Friday, December 05, 2008 - 11:34 am:   Edit Post

Any chance the positive and negative leads from the bridge pickups were reversed when connected to the preamp circuits, so that instead of cancelling the hum, it is actually increasing it? Not sure exactly what type of connectors they are, so it may not be possible to reverse them. Just a thought...
Senior Member
Username: dela217

Post Number: 927
Registered: 6-2002
Posted on Friday, December 05, 2008 - 2:43 pm:   Edit Post

If the wires on one of the pickups were reversed, the pickups would then be out of phase. That would lead to no low end and a VERY nasal tone. Trust me.
Senior Member
Username: kungfusheriff

Post Number: 771
Registered: 8-2003
Posted on Saturday, December 06, 2008 - 7:53 am:   Edit Post

My basses have no shortage of low end, or any major gaps in the frequency response as one would expect from out-of-phase wiring, so I doubt that's it.

Checked both basses last night. The '82 has decided to be silent, so I guess that's good. The '95 did not behave any differently after having the pickup leads switched. Its buzz is muted if the tone controls are rolled back far enough with the filters disengaged. The later bass has a lot more going on in the upper frequencies than its' older siblings, even with the controls set identically. Was there a fundamental change in the electronics between 1982 and 1995? The vastly different scale lengths and woods don't account for this difference in sound, at least in my mind.
Intermediate Member
Username: bigyouth

Post Number: 139
Registered: 7-2006
Posted on Sunday, December 07, 2008 - 12:56 am:   Edit Post

I have the same probleme on my neck pickup
Senior Member
Username: kungfusheriff

Post Number: 776
Registered: 8-2003
Posted on Saturday, December 27, 2008 - 4:06 pm:   Edit Post

OK, finally an update with some new info. Everybody got their Sherlock Holmes hats on?
I'm begging to suspect that the '95 Series 2's problem stems from one or more broken connections hiding somewhere in the circuitry, as a lot of the noise I am getting sounds very much like an open circuit.
There is quite a bit of play in the five-pin connector socket, specifically the pins themselves and the backboard they are mounted to. They do not move individually, but rather shift back and forth as one unit. On Mica's suggestion I located and tightened the screw that holds this assembly into the jack's outer casing, but it comes loose again almost immediately. When the cable's plug is allowed to shift in the jack, I get loud static and occasionally the sort of humming I associate with a guitar cable plugged into a loud amp, but not plugged into a guitar.
Additionally, I'm getting thumps and weird noises when I undo the backplate screws with the amp on and the bass plugged in, and after getting the cover off I get loud hums if I manipulate the wide, rainbow-colored wire set that leads from the controls to the PF6 circuit card. Tapping the wires where they are soldered to the number 2 and 3 pins of the cable jack also rewards me with a loud hum.
I'm starting to become sure that the least I should do is replace the jack; anyone done this at home? How bad was it? Mica, how much is the part? Any other thoughts on what the underlying problem might be? Thank you all once again.
Advanced Member
Username: dfung60

Post Number: 371
Registered: 5-2002
Posted on Saturday, December 27, 2008 - 10:29 pm:   Edit Post

I'm not sure which kind of 5-pin jack your '95 bass has, but it's not that unusual for there to be a little bit of motion of the plate that the pins are mounted on relative to the shell on any Cannon-type connector. The theory here is that the pins can shift as a group when mating with the plug, otherwise everything would have to align perfectly to make the connection. Some jacks have more wiggle than others. The relationship of the pins relative to each other must be absolutely stable.

An interesting test for you to run would be to see how things sound when you connect on the 1/4" jack. By '95, the default wiring was that the 1/4" jack is mono output (e.g, you can hear both pickups with a regular 2-conductor guitar cable). On instruments from the 80's the 1/4" jack is usually stereo, so if you plug in a regular guitar cable, you'll only hear one pickup, usually the bridge one. To get both pickups on these older instruments, you need a 3-conductor 1/4" plug to two 2-conductor jack y-cable.

If your bridge pickup sounds OK on the 1/4" cable, then I'd start suspecting the 5-pin cable, DS boxes or the 5-pin jack. Cables will almost always be a more likely cause of failure than the connectors since the internal connections bear the brunt of you walking a foot too far from your amp.

You haven't talked about the specifics of your amp setup yet, but if you have a stereo rig with the pickups routed differently, you should check those paths as well. When you switched the bridge and neck pickup leads you mentioned that the bass didn't behave differently, but that answer was ambiguous. Did that mean that the bridge pickup continued to be the noisy one or did you mean that the neck pickup became the noisy one? If you have a stereo amp setup, and the bridge pickup really had a problem, you'd expect the noisy sound to be coming from the speaker that the neck pickup normally plays through without noise. If you swapped leads and the noisy signal stayed in the same channel, then it's not actually the pickup that's the problem. If you have a mono setup where you take the mono out from the power supply, then diagnosing by swapping is a little harder to detect (you need to gently tap the pickup face with a screwdriver to identify which pickup is which).

If you poke around in the electronics while the amp is active, it's not necessarily odd to get thumps or noise when you move the wiring (in certain cases, the wiring will seem to be microphonic). If you poke around while the amp is on and something completely cuts out or radically drops in level when you move a wire around, that would be a sign of a bad connection. When you touch the jack pins and get hum, that would be normal; again, if the sound cuts out entirely that would be an indicator of a bad connection.

Try this stuff out and report back. You've seen what the internal wiring looks like - the Series bass easily has the most complicated 1/4" jack wiring of any instrument in existence, so it would neither be fun nor cheap (I guess I mean that in absolute rather than relative terms!) to try to replace it.

David Fung
Senior Member
Username: kungfusheriff

Post Number: 777
Registered: 8-2003
Posted on Sunday, December 28, 2008 - 7:49 am:   Edit Post

Hi, David.
When time permits I'll dig out a few nine-volts and and 1/4" cable and see what happens. As things are, I get noise no matter which cable or power supply I use, and whether I run the bass mono or stereo. I gigged the bass last week and didn't notice any oppressive noise, but at home yesterday I had to put it down and play another bass.
Going back to the lead-switching experiment, after I made the swap the noise was coming out of what had been the neck-pickup output, which the bridge pickup was then connected to. Is that more clear?
Senior Member
Username: lbpesq

Post Number: 3450
Registered: 7-2004
Posted on Sunday, December 28, 2008 - 8:41 am:   Edit Post

David wrote:

"you need to gently tap the pickup face with a screwdriver to identify which pickup is which."

Another method I've found that really works well is to use a tuning fork. Bang the fork to get it going, then just hold it over the pickups. It will be very obvious which pickup is working and which isn't.

Bill, tgo
Senior Member
Username: kungfusheriff

Post Number: 778
Registered: 8-2003
Posted on Sunday, December 28, 2008 - 11:24 am:   Edit Post

Bill, the problem isn't with a lack of signal from either pickup but rather with an excess of buzz.
The jack issue may be just a red herring...I disconnected the elderly cable I usually use, which came with one of the older basses and works just fine with them, and substituted my newer cable, one of the ones with the black-anodized connectors. No crackles or other major problems. This is the cable that I used, without incident, on the last gig. Maybe the tolerances changed by a half-millimeter between '82 and '95?
The '95 bass still buzzes with the newer cable, especially with the tone knobs at 10 and both filters off, but the noise is much reduced with the newer cable.
Username: davehouck

Post Number: 7312
Registered: 5-2002
Posted on Sunday, January 04, 2009 - 7:20 pm:   Edit Post

"after I made the swap the noise was coming out of what had been the neck-pickup output, which the bridge pickup was then connected to"

So the problem is not the pickup.

Do you have a power conditioner in your rig?
Senior Member
Username: kungfusheriff

Post Number: 779
Registered: 8-2003
Posted on Tuesday, January 06, 2009 - 6:19 pm:   Edit Post

No rig, Dave...just the bass into the cable, the DS5, and stereo into the amp.
Username: davehouck

Post Number: 7317
Registered: 5-2002
Posted on Tuesday, January 06, 2009 - 7:42 pm:   Edit Post

I'm still thinking about the difference between the gig and home. I think I would try taking basses and rig to a friends house and see what happens. Also, maybe someone in the band can loan you a power conditioner; or you can surreptitiously borrow the one in the PA.

Oh, and it just occurred to me. Have you tried swapping out the cables that run from the DS5 to the amp?
Senior Member
Username: georgie_boy

Post Number: 642
Registered: 8-2005
Posted on Sunday, January 18, 2009 - 6:30 am:   Edit Post

Bigyouth has asked me to find out the impedance of a neck Series 1 pickup from around 1982?

Can anyone help??
He would have posted this himself, but his English is not so good



Topics | Last Day | Last Week | Tree View | Search | Help/Instructions | Program Credits Administration