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Unread 08-04-2009, 12:57 PM   #1 (permalink)
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What are typical causes of feedback?

Two guitars with dual humbuckers (from two different guitar manufacturers) are tested with the same amp at the same settings. One generates no unwanted feedback, the other squeals with very little prompting.

So what is/are the most likely reasons why one humbucker-equipped guitar would generate feedback while the other wouldn't?

I'm asking in this forum because my initial speculation is that it is related to the pickups somehow.
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Unread 08-04-2009, 02:53 PM   #2 (permalink)
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Re: What are typical causes of feedback?

Any open space between the pickup and it's cover will be microphonic and cause some wild feedback. I'd suspect that what you have going on there.

To fill the gap I've used everything from wax, tape, a piece of cloth even a small bead of dap tub n tile. It all worked.
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Unread 08-04-2009, 02:56 PM   #3 (permalink)
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Re: What are typical causes of feedback?

I have this problem with my LP, and I still have it after changing the pickup from a Burstbucker Pro to a 500T, both of them have been un-covered.

When I play through the same amp with my Fender Strat with a Dimarzio Super D Humbucker it hardly feedbacks at all....

Any idea why?
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Unread 08-04-2009, 03:05 PM   #4 (permalink)
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Re: What are typical causes of feedback?

My burstbucker pros came heavily potted. Not sure why one would squeal without a cover. Unpotted pickups can feedback pretty easily.
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Unread 08-04-2009, 03:24 PM   #5 (permalink)
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Re: What are typical causes of feedback?

Loose components, crappy taping job on the coils, loose polepiece screws will definately cause it.
Proximity to the amp, if you have your amp directly facing you, can cause it. Especially at high volumes. Even with heavily potted pickups.

A theory of mine (although I can't prove it) is that the nickle plating on covers also causes feedback. Nickle is magnetically reactive (highly so) and it stands to reason that if the cover vibrates at all, it's the nickle plating that causes the feedback issues. Sure, there's nickle in nickle-silver, but the amount is somewhat small.
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Unread 08-04-2009, 03:26 PM   #6 (permalink)
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Re: What are typical causes of feedback?

Don't forget, that tubes also become microphonic. Some guys think that it's the pickup squealing, when it's the tubes.
Had this problem once with Rick Derringer...

I've got microphonic tubes in my Univalve right now. Squeals like a bitch. But sounds freaking great.
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Unread 08-04-2009, 03:51 PM   #7 (permalink)
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Re: What are typical causes of feedback?

My test amp is just a little solid state practice amp, so no tube microphonics to be found there.

I am considering replacing the stock pups with a SD Distortion and a DiMarzio Super Distortion anyway, both of which I've used before with great success. The squealing guitar is not a LP, nor is it even a Gibson, btw...
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Unread 08-04-2009, 03:55 PM   #8 (permalink)
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Re: What are typical causes of feedback?

You can sometimes locate the cause of the squeal by placing a finger on the pickup and moving it around until the squeal stops. As many have said, commonly a problem with the covers.

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Unread 08-04-2009, 04:48 PM   #9 (permalink)
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Re: What are typical causes of feedback?

potting time or lack there of. Nothing between the cover and the slugs, such as tape and a re pot once the cover is installed.
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Unread 08-06-2009, 01:21 AM   #10 (permalink)
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Re: What are typical causes of feedback?

So after some more time with the guitar I find that one string or another (so far its primarily been either the low E or the G string) starts to vibrate on its own and generates harmonic feedback. Touching the pickup covers has no effect, but resting a finger on the offending string stops it, of course.

So, why do strings on this particular guitar vibrate to the point of feedback, but other guitars of mine don't do this? Now I'm beginning to think that a pickup mod won't help this after all.

Thoughts?
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Unread 08-06-2009, 06:26 AM   #11 (permalink)
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Re: What are typical causes of feedback?

OK, that's the form of feedback that people think of as good. You get rid of it by moving away from the amp. There is no "cure" for harmonic feedback, but you can control it by damping the strings.
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Unread 08-06-2009, 07:37 AM   #12 (permalink)
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Re: What are typical causes of feedback?

Sounds like those strings are a little more alive than what you are used to. It can be a good thing...learn to keep it under control and use it to your advantage when you want to.
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Unread 08-06-2009, 04:34 PM   #13 (permalink)
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Re: What are typical causes of feedback?

Yeah, I guess these strings are quite a bit more "alive"...I mean, just plugged into a Roland Micro Cube (gain at about 80%, volume at about 35%), this guitar's low E string will squeal like a banshee. I've plugged in about 4 or 5 other guitars and none of them feedback like that.

What is going on structurally (as opposed to electronically) that makes one stringed instrument more susceptible to this than another?
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Unread 08-09-2009, 10:55 PM   #14 (permalink)
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Re: What are typical causes of feedback?

Here's an update on this:

I eliminated the out-of-control feedback problem in the offending guitar by replacing the stock pickups with a Seymour Duncan Distortion in the neck position and a DiMarzio Super Distortion in the bridge position, both of which I had laying around from previous projects. I also put on a set of Dunlop Zakk Wylde 10-46s.

No more feedback!
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Unread 08-09-2009, 11:50 PM   #15 (permalink)
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Re: What are typical causes of feedback?

Well... that solved your problem, but didn't really answer your original question.

I wonder what you'll do now with the offending pickup(s)?
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Unread 08-10-2009, 03:41 PM   #16 (permalink)
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Re: What are typical causes of feedback?

Quote:
Originally Posted by 180gROC View Post
I wonder what you'll do now with the offending pickup(s)?
The only thing to like about the original pickups is the covers, which have a rather attractive etched design on them. I will keep them stored away in case I ever decide to return the guitar to stock, but otherwise these pickups are better off never being used IMHO.

(The guitar in question, btw, is a standard production run version of the Dean 30th anniversary Flying V.)

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