Screaming Feedbacks on loud volumes

burt777 · #1 08-31-2008, 02:27 PM

I'm in desperate need of guidance.

On stage i'm haunted by these screaming feedbacks every time i kick open just a little distortion. It's not string-feedback, but higher in pitch, and it develops much faster. If i play it's gone, but as soon as i stop playing, it's there again.

Here's my chain:
[Jem7] - [Senheiser wireless] - [Boss GT-5] - [Roland ST-50 amp] - [Rode NT1 condensor mic] - PA, whatever we're playing over that night.

I know almost any of these ingredients are suspicious, and i really want to upgrade, but i have to know i'm solving the problem, and for that i must get an understanding of the problem.

I tried searching the forums for the word "feedback", but i get overwhelmed by auction-related "feedback". Can somebody give me a pointer to what this is, how it's solved or where to start searching these forums or any other part of the internet?

**elcid** · #2 08-31-2008, 02:31 PM

Check for microphonic pickups. Also common sense, but the post doesnt say it, dont put your pickups right in front of the amp.

Vim Fuego · #3 08-31-2008, 02:56 PM

Have a look at this thread:

http://www.jemsite.com/forums/f21/ev...vwh-28471.html

The question was about wobbly pickups but a couple of the posts (including mine #9) recommended packing the pickups with foam. I did this to stop the squealing feedback you describe, I only had it with the bridge so that was the only pickup I put foam around.
Jim

burt777 · #4 08-31-2008, 05:18 PM

I did some experimenting:

I ignored my housemates for a moment and recreated the feedbacks in my room. It doesn't stop if i push, hold or "palm mute" the pickups. I think this means that it's not a microphonic-issue. It also means that adding foam is not going to save me.

I removed the Boss GT-5 from the chain and cranked up the gain of the amp, and i get them too. I can keep the GT-5. (-:

It changes drastically if i turn the guitar around. Also, it's mainly when my PU's are really in front of the amp speaker. If i lift the guitar above the amp, i need much more gain to get the feedbacks.

Magnetism? I wanted to buy a bigger amp (the ST-50r is pretty small), but if magnetism is my problem, i am afraid i'm going to have even more trouble... )-:

Vim Fuego · #5 08-31-2008, 05:35 PM

OK, good testing! I suppose it might still be the coils of the pickups rather than the piclups themselves but I doubt it.
Can I suggets you eliminate the wireless? Just use a decent lead into the gt-5 and you can eliminate that as a source of the noise. If it turns out that the wireless is to blame then I believe some of them have a trim control on the transmitter to match the signal level perhaps that needs adjustment?
Jim

Dino · #6 08-31-2008, 05:43 PM

Dude, if you stand right in front of the amp it's going to feedback when you crank it up. Thats just what happens. Get a line 6 variax is about the only thing you can do anything with pickups will feedback.

Dino · #7 08-31-2008, 05:50 PM

Doesn't that GT-5 have a noise gate?

burt777 · #8 08-31-2008, 06:11 PM

Yeah and yeah. But no. (-:

The GT-5 has a noisegate, and i'm using it, but often the feedbacks are too loud for it to get them. I can adjust it to be more agressive, but you start to hear the noisegate and i still get a very short squeek at the beginning of every 'silence'.

I know feedback at loud volumes is inevitable, but it still feels 'unfair'. I mean... Vai plays Jem guitars on louder stages, with louder amps, with much more gain, and i don't think he avoids his amps by a range of 3 meters (or am i wrong on this?). I never heard these kinds of feedback from him or any other guitarist playing on a bigger stage.

In my testing i already omitted the Senheiser wireless. For a second i thought it 'helped' causing the feedbacks, but without it, i can still make the feedbacks more easily than i think should be possible.

Dino · #9 08-31-2008, 06:31 PM

face away from the amp.

burt777 · #10 09-02-2008, 08:15 AM

Done some more testing. I recreated the feedbacks, put pillows and blankets over my amp and they were gone. This proves the feedback is sound-based, not magnetic (i made that up myself ;-> ). I also got a pickup out of my guitar and found it's already waxed. It's an old Jem (a '97 7BSB), so maybe the wax is worn, but i'm not very confident about rewaxing, and before i get going, i would really like to know it's likely this will solve the problems.

When i hold the pickup in front of the amp it still screams (well, first it didn't, but then i found out i ruined the wiring when i removed it... )-: ). Even when i press it, hold the springs that keep it in the pickguard (or remove those and hold the PU in my hand).

Is there any way to measure whether my PU's are _too_ microphonic, or am i just playing too loud and being too careful with the noisegates when using lots of distortion and gain?

7 Dying Trees · #11 09-02-2008, 08:42 AM

OK, i had this same issue with my PWH. I'd play, no squealing, stop, and the high pitched noise would start. It's most definately one of two things:

1) Microphonic pickups. This is easy to fix, it's basically the breakdown of wax inside the pickup and happens. Buy yourself some beeswax, and parrafin wax (candle wax). Get a tin (empty tin of canned tomatoes or whatever, you'll definately have one) and a candy thermomiter.

Follow these instructions: http://www.projectguitar.com/tut/potting.htm

And you're done. It's easy, and you'll find you'll have enough wax to last you forever-ish

I did it with mine, and now the squealing is completely gone! And my pickups were waxed as well. It's basically air in between the wax in the pickup. So even if it looks waxed you'll have that problem sometimes.

2) Microphonic preamp tube. Open the back of the amp so you can get to the preamp tubes. With the amp on, tap each one with a pencil see if it makes an audible sound through the amp, or get a spare tube, and replace them one at a time.

One of these two should be your problem, and both are easy to fix

7 Dying Trees · #12 09-02-2008, 08:44 AM

Oh, one more thing, putting blankets on the amp will lower the volume, and the microphonics is more what happens at high volumes, so I still reckon for 95% certainty that repotting your pickups will sort it out.

Best way to also test is get another guitar, and see if that exhibits the same problem, should narrow it down to the amp or the guitar