SG Bass: To Feed Or To Feedback, that's the question ..........

[Droombolus]

Sound checking my Standard SG and Supreme Natural SG Bass on the same rig at a gig yesterday I noticed the Standard was on the edge of feedback while the Supreme had no such problem. Both basses were plugged in with the exact same settings on the amp and pre-amp with both basses' PUPs in my fave sweet spot setting and there was no real diffrence in the volume coming from the rig.

That got me curious so I set the volumes on the PUPs way open on both basses and the same thing happened. That's got me wondering if there's a connection between the diffrence in the woods ( full mahogany / 50/50 mahogany & maple ) used for the body or maybe the density ( and weight ) of the wood used. Or whatever ...... 

Anybody's got any insights in this ?

[Iome]

Maybe a pickup issue?

[Dave W]

Do you have a meter to measure the DC resistance of the pickups separately on each bass? No need to unsolder anything, you would just be looking for any obvious differences between the two humbuckers and two minibuckers.

[Droombolus]

Yes, I've got a meter but I'm not very technical sooooooo ..........how do you measure the PUPs without unsoldering the PUPs ? On the pots ?

[Rob]

I'd try tapping the pickups with a pencil first.  Turn vol to max (am down a bit ) and just click away. 

[Dave W]

Yes, I've got a meter but I'm not very technical sooooooo ..........how do you measure the PUPs without unsoldering the PUPs ? On the pots ?

Just plug in your cable and measure resistance between the tip and sleeve. On each bass, turn one pickup all the way down when measuring the other, then if both basses are okay, watch as you turn the pots to see what's happening. You're not after accurate out-of-circuit readings, you're trying to see if there's any obvious difference between the basses.

[Wilbur88]

The only SG I've had was a Supreme Fireburst and that used to squeal like a pig at loud volumes even when I had my back to the amp.  It was really annoying.

[Droombolus]

Just plug in your cable and measure resistance between the tip and sleeve

There's not much diffrence in the results. The Standard measures Sidewinder: 8.98K / Mini HB: 5.98K and the Supreme Sidewinder: 8.92K / Mini HB: 5.89K. Don't think the "problem" ( and I don't really think of it as a problem, I'm just curious ) lies there, so I come back to my 1st question .... Is it possible there's a relation between the sort of wood or the density / weight of the wood of the body and the sensitivity of an instrument for feedback ?

[uwe]

I venture forth the contribution that the Supreme's body should indeed be a whole lot stiffer and less prone to vibration and resonance - not only because of the maple content but probably more importantly due to the sandwiched body halves. That is a type of construction - and by some people derided for it - that pretty much kills any frequency escalation of the type to lead to feedback.

[Droombolus]

Sounds plausible Uwe 

[Dave W]

There's not much diffrence in the results. The Standard measures Sidewinder: 8.98K / Mini HB: 5.98K and the Supreme Sidewinder: 8.92K / Mini HB: 5.89K. Don't think the "problem" ( and I don't really think of it as a problem, I'm just curious ) lies there, so I come back to my 1st question .... Is it possible there's a relation between the sort of wood or the density / weight of the wood of the body and the sensitivity of an instrument for feedback ?

Then whatever it is, it's not in the pickup output.

I venture forth the contribution that the Supreme's body should indeed be a whole lot stiffer and less prone to vibration and resonance - not only because of the maple content but probably more importantly due to the sandwiched body halves. That is a type of construction - and by some people derided for it - that pretty much kills any frequency escalation of the type to lead to feedback.

It's stiffer, no doubt about that. That stiffness might be suppressing the tendency to feed back. But that doesn't explain the cause of the feedback. Could be some fault within the pickup, could be something different about the pickup mountings, or something we haven't considered yet.

[dadagoboi]

Very common cause of feedback is bad potting job.  Gibson has been known to have inconsistent results in that area.

[ThunderBucker]

Hi guys, Thunderbucker here.  The usual reason an electric bass or guitar feeds back is due to the pickups, not the wood (an acoustic instrument can feedback due to the sound board being moved by the amp sound, just as the string motion would)

Pickup feedback is caused by something in the magnetic field of the pickup being able to move. Remember that the pickup works because the iron string is moving in a magnetic field, and that there is a coil of wire that senses the changing magnetic field.  And either changing the magnetic field, or moving a coil in it (the principal that a generator uses to make voltage and current) can cause an output.

So if anything magnetic can be moved by the amp sound (this can be the metal pickup can, nickel silver is slightly magnetic), or if any of the coils can move, then the pickup can become microphonic, that is, behave like a microphone. and of course, mics can feedback.

The most common cause is the potting (or lack thereof) of the coils.  Usually, the coils are wax potted (dipped in molten wax for 15-30 minutes, sometimes with a vacuum pulled to help get the wax into all the crevices).  You can see this in the Seymour Duncan you tube tour.  This is time consuming and messy, so companies often try to cut corners on this.  When CBS bought Fender, it was one of the first processes they cut, as a result, post CBS guitars fedback badly unitil they realized they had to bring back the potting process.  I had a CBS tele with this problem. Sounded great, squealed like a pig.

You can test pickups for microphonics by tapping lightly on the pickup with something non-magnetic (don't use a screwdriver!).  A wooden rod would be ideal (don't hit the strings, hold them very still).  Even with a well potted pickup, you will still hear some of the tapping come out of the amp.  But this test will clearly distinguish a very microphonic pickup from a much quieter one.

[Wilbur88]

^  Gee thanks for that insight.  My T-bird is also prone to the odd squeal.