Amp breaks up on "D" note

Rusty Walker · From: Markham Ont. Canada, R.I.P.

Any amp techs who may have a clue.I have one of the original hand wired Webb amps that has been a joy to me for 20+ years.I recently had an accident with the speaker-a 15" JBL.At about the same time ,something in the output stage broke down.I had the speaker reconed and the amp repaired.Both techs are very reputible.I found that the amp was breaking up and so I returned it to the amp tech who found dirty connectors,cleaned & tested it.On the gig yesterday it was still breaking up.Today I have bypassed all effects.I find that it only breaks up on a low or mid "D" note.It will do it onC# & D#,but not to the same degree as D.Something about that frequency seems to trigger the break-up.Any ideas?

Ernie Renn · From: Brainerd, Minnesota USA

I can't say exactly what is causing the break up on that note, but here's what happened to me (in about 1980):
I started hearing a buzzing on a few lower notes. I had a tech go thru the amp and he found nothing wrong. The speaker, which always worked fine, MUST be the problem. It looked fine, though. After about three days of checking this and that, I found that the dust cover in the center of the speaker was coming loose. If I played certain low notes it would buzz. It sounded fine for most notes, but when you'd get to the lower register a few would cause it to vibrate. I used some kind of glue, I don't remember what, and used a toothpick to apply it. Problem solved.

I'd check this, as even a newly re-coned speaker can have this problem. Be carefull though, so you don't dent it.

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My best,
Ernie

The Official Buddy Emmons Website
www.buddyemmons.com

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Ernie's right...that's a good tip! Usually, these problems at a single frequency or note are mechanical rather than electrical. If it's not the dust cap, it could be the speaker itself. Sometimes, the speaker can be over-tightened, or unevenly torqued when installed, and this will warp the basket, causing strange buzzing noises. If you don't have another speaker to hook up to temporarily, try loosening the speaker mounting screws, and then retighten them evenly and firmly, like you do car wheels (tightening opposite, instead of adjoining screws, 'til they're all tight).

If that's not the problem, then you might have to remove the chassis, and tap around with something plastic (like a Bic pen) while the thing's on. Usually, you can locate where there might be a loose connection using this method. Now, if you don't feel comfortable...or safe...doing this, (meaning---you've never done it before) take it back to the tech, and let him do it. And remember to describe the problem in detail.

Terry Downs · From: Wylie, TX US

Rusty, another approach would be a process of elimination of the amp sections. It seems suspicious that the problem started with the speaker replacement. Speaker repair is not a 6 sigma process. I would do the following to isolate the failure.

1. Connect a known good speaker cabinet to the amp to isolate the speaker.

2. Make sure you are going straight onto the amp with a known good cord...no volume pedal, no effects.

3. If that amp has pre-amp out/power amp in jacks, connect a power amp and speaker to the pre-amp out. Test the bad notes.

4. Connect the line out of a stereo, or the preamp out of another amp to the power amp input and see how it sounds.

Breaking up at a specific frequency means the failure has a high Q. The mechanical parts of a speaker that can fail may have a very high mechanical Q. Cracked parts can exhibit that type of response whereas interferences are usually noisy at many frequencies. Other high Q failures can be decoupling networks.

Hopefully you can knock the problem down to the component or section of the amp that is the problem.

Good luck,
Terry

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Terry Downs
http://nightshift.net
terry@nightshift.net

Jim Cohen · From: Philadelphia, PA

A while ago, my Nashville 400 would break up only on middle C#. I discovered that it was a loose Molex connector to the speaker. I simply pushed that in tighter and, voila, it was solved. Of course, your mileage may vary!

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www.jimcohen.com

Ernie Renn · From: Brainerd, Minnesota USA

You might also want to check: Make sure the screws, (holding the amp itself and any cabinet screws,) are tight. It may be that your cabinet is vibrating at a certain frequency. Check the grill to be sure it's pushed in all the way. I'm not familiar with how Webb mounts the grill, but on Peavey they use glorified Velcro. It works, but if the grill isn't snapped into place, it can buzz.
Like Terry's post, find where it "isn't" then you can hone in to where the noise is coming from. Be careful: It might be something silly! (I had a buzz one night and it was a screw on the back of the speaker magnet... Silly!)

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My best,
Ernie

The Official Buddy Emmons Website
www.buddyemmons.com

Doug Earnest · From: Branson, MO USA

I don't know if a Webb has any tubes, but my Fender was making a bad noise on the D notes also. It turned out to be a bad preamp tube. My noise sounded more like glass rattling.

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Doug Earnest
Zum2000U12,Sierra12,Sho-Bud ProII D10

Rusty Walker · From: Markham Ont. Canada, R.I.P.

Thanks for all your input,Guys.I really appreciate it.I think you may be correct about it being a mechanical prob.I'm going to take it to the speaker tech and get him to put a tone generator on it,since I don't have one.Should be able to find it that way.Doug,the WEBB is all transistor.But I know what you're saying about tube amps.The tubes will go microphonic.I,ll let ya'll know what happens.

Rusty Walker · From: Markham Ont. Canada, R.I.P.

With the tone generator on,all the bottom end broke up.So it's a circuit prob.Back to the amp tech who will check for cold solder joints.Another fall fair gig this weekend which will put it to the ultmate test.Outdoors-eggggggggggh!Pray for me!!! Rusty

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