Hum

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Hum

Postby jfh4242 » Thu Oct 04, 2018 1:05 pm

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Hello Ladies and Gents, I'd like to pool the collective wisdom of the site!

My beloved SB2 Trib started humming yesterday. At first it was low and now it is quite loud. I imagine there is a loose connection somewhere in the electronics.

I'd like to resolve this myself if possible. I could take it in, but I figure that I should at least try it myself before giving up.

I tried to eyeball the connections, I did not see anything loose. Where does one usually start with this?

Concerning pic number two, the protruding thing on the right was touching the male end of my quarter inch wire when plugged in...is that ok? I imagine so, because it seems to be keeping the quarter inch wire inside.

How many connections should there be to the input jack? I notice that my bass has one, that white wire. Is that ok? Thanks!

John
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jfh4242
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Re: Hum

Postby Ken Baker » Thu Oct 04, 2018 1:49 pm

jfh4242 wrote:Where does one usually start with this?


By asking questions. Like:

    Under what conditions do you hear the hum? Touching nothing on the bass? Touching the strings? Touching the bridge?

    Is it a true hum, which is about a low B on the A string?

    Are there any notable high frequency sounds coming through as well as the hum?

Concerning pic number two, the protruding thing on the right was touching the male end of my quarter inch wire when plugged in...is that ok? I imagine so, because it seems to be keeping the quarter inch wire inside.


That would be the "TIP" connection of the jack. It is supposed to be in contact with the "TIP" of the plug; that "quarter inch wire" you speak of.

How many connections should there be to the input jack? I notice that my bass has one, that white wire. Is that ok? Thanks!


There should be two connections to the output jack. One of them would be the white wire, as shown. The other would be a ground connection. In your bass, the ground connection can be done a couple of different ways: (1) A wire lead from one of the pot cans to the ground lug of the jack or (2) Physically mounting the jack to the grounded foil on the back of the pickguard, which can be quite problematic.

Based on your second image, the jack is not grounded or has a poor connection to ground. Whoever wired your bass used method two. In an of itself, this is generally workable so long as the jack never rotates in its mounting hole. When rotation does occur, which is all too often, the connection to the grounding foil wears through. Over time it gets worse and worse until the foil is worn through to the underlying plastic of the pickguard, at which point the jack no longer has a good ground connection. Because the jack is a key component of grounding and is no longer in contact with ground, the instrument has an open ground and hums.

Look carefully at the underside of your jack and you'll see that what I described above is what's happening. The jack has loosened and spun in its hole and has been repeatedly spun back down to tighten on the pickguard. This cycle has repeated enough times to wear through the foil to the point that the physical connection to the foil is compromised.

The fix is to (A) tighten the jack so that it can no longer spin in its mounting hole, then (B) solder a short green or black lead from the free solder lug on the jack to the back (can) of one of the pots.

This is, of course, an Internet diagnosis/eval. It's worth every penny you paid.

Ken...
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Re: Hum

Postby deltafred » Thu Oct 04, 2018 2:20 pm

John

As Ken says "I don't have the bass on front of me" so I'm only guessing.

If nothing is obviously wrong then one possibility is that the connection between the ground wire and the bridge has gone high resistance.

If you have a multimeter (every bassist should own a multimeter) put it on the lowest resistance range and put one probe on the bridge and the other on the jack socket nut (or plug in a jack lead with a metal plug body and meter to that.

If the resistance reads more than a couple of ohms then it's time to remake the bridge ground, see bridge grounding.

fred
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Re: Hum

Postby jfh4242 » Sat Oct 06, 2018 5:44 am

Gentlemen.

Thank you for your precious replies. Your two presence and guidance are some of the best things in this amazing site. We are fortunate to have you both.

I will be taking my bass to a friend who is very knowledgeable about this stuff this weekend and we will see what's up, starting with your comments. We will investigate and I will learn how to resolve this for myself next time, so I don't have to run to him for help. Or hassle you!

Thanks again!

John
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Re: Hum

Postby TDR1138 » Mon Oct 08, 2018 12:59 pm

The top photo does appear that something was at some time soldered to the sleeve terminal on the jack. I agree with Ken and Fred that the foil was probably grounding it at first and got worn through due to some rotation of the pot. Should be a quick fix to run a ground wire from that terminal on the jack to the back of the tone pot casing.
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Re: Hum

Postby Ken Baker » Mon Oct 08, 2018 2:26 pm

TDR1138 wrote:Should be a quick fix to run a ground wire from that terminal on the jack to the back of the tone pot casing.


In fact, it would be an even better fix to extend that ground wire from the jack to the tone pot can to the volume pot(s) can.

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Re: Hum

Postby TDR1138 » Mon Oct 08, 2018 2:41 pm

Ken Baker wrote:
TDR1138 wrote:Should be a quick fix to run a ground wire from that terminal on the jack to the back of the tone pot casing.


In fact, it would be an even better fix to extend that ground wire from the jack to the tone pot can to the volume pot(s) can.

Ken...


Looks like there is a green coaxial cable that appears to include a ground wire connecting the volume pot casing to the tone pot (assuming the casing, but hidden behind the capacitor). Just doesn't make it to the jack. But I think you'd be redundant in wiring a ground between the volume pot and tone pot.
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Re: Hum

Postby Ken Baker » Mon Oct 08, 2018 3:03 pm

TDR1138 wrote:Looks like there is a green coaxial cable that appears to include a ground wire connecting the volume pot casing to the tone pot (assuming the casing, but hidden behind the capacitor). Just doesn't make it to the jack. But I think you'd be redundant in wiring a ground between the volume pot and tone pot.


I didn't look at that; too focused in on the jack's connection to the plastic pickguard.

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Re: Hum

Postby Ken Baker » Mon Oct 08, 2018 5:01 pm

Just spent some time looking a bit more closely at the photos. It's really hard to see, but it appears that the shield of that coaxial shielded lead is broken (or maybe beat up badly and then broken) at the tone pot. The leftover "wire" on the sleeve connection of the jack looks like it might be pretty finely stranded, much like the braid of a shielded cable.

--So--

I'm wondering if there was an extension of the braid of that shielded lead that ran to the sleeve connection of the jack. Then, in all the twisting and beating and banging on the jack when it got loose on the pickguard, that braid broke. The break would likely only be at one end, so it would be interesting to learn what happened to the rest of it.

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Re: Hum

Postby jfh4242 » Wed Oct 10, 2018 5:23 pm

Hello Gents!

So it was a grounding issue. There was a loose wire that was "stripped" off the tone pot. We found it, soldered it back, all is good.

I feel stupid that I did not see this myself. Sigh.

Best part is that through the collective wisdom of this site AND the expertise of my friend, I think I learned enough to be able to take care of this myself next time.

Thanks again to everyone who contributed!

John
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