Weird Feedback Problem - Help?!?

[Paul Marossy]

This is really weird. I'm hoping someone can help me with this...

My church has moved into a new bldg. and my setup is having major problems with feedback, and to a lesser degree, hum.  :cry:

Here is the details:

The stage is kind of a 24"x24" modular raised floor system. Some of the tiles are carpeted and some have linoleum on them. My amps sits on an area that is linoleum. There is also a concrete floor (soon to be carpeted), and walls that are very reflective in terms of sound absorption (eventually we'll get some acoustic panels put in). My amp is about 18" from an interior partition. EQ'ing is kind of a pain, but I've got that figured out. There is a PA system monitor about 10 feet away from the amp, which is miked. I only mention this stuff because it may be a contributing factor.

Here is what I found today - the weird stuff: I have a Black Cat OD-1 clone, a TS808 clone and a Boss Metal Zone on my pedal board. I have not changed anything from how I had it in our old building, which was carpeted, acoustic ceiling, etc. I get a hum with all three of them, the Metal Zone being the most noticeable. This is the one that is causing me grief. If I just stand there and not play anything, it's starts to feedback almost immediately, kind of a low mid sound. No matter how I EQ it or my amp, I get this feedback. Now is where things get strange. The lighting in the building are mercury vapor or something like that. They have transformers right at each fixture. Apparently, a few of those transformers are bad, so they have a pretty loud hum. My pedalboard, without any guitar plugged into it picks up this hum! When I plug my guitar in, it goes nuts. Microphonic city. I tried changing the position of the amp, my guitar in relation to the amp, different pickups, different preamp tubes, tilting the amp back, leaving it upright, no matter what I do, I still get this feedback. I get a hum even with the pedalboard plugged into the amp's effects loop and no guitar plugged in. So I have concluded that it must be those #$%&*@# transformers casusing all of this to happen.

So, I have developed a theory. Even though all of my effects are in metal enclosures and I have shielded cable connecting everything, it seems that somehow, this EMI being projected from these bad transformers is being picked up by my pedalboard and being amplified (of course). But what it appears to be doing is causing my Metal Zone to somehow go into oscillation and then the amp starts to feedback as well, until it reaches a resonant frequency and stays there.

Is it possible that a bad case of EMI could cause all this trouble? Is there anything I can do to stop this? (besides not using the Metal Zone)

[ExpAnonColin]

Did you try a parametric EQ?  Depending on how wide the subharmonics and harmonics range that could help you, but probably not all too well.

If your strings are not resonating as the amp feeds back, then it is definitely an external factor.  It IS possible that your pickups are the ones picking up the "transformer hum", as well as it could be your setup.  Although you say you tried different pickups... well, I suppose it's possible, pickups can function as microphones at high enough gain (have you ever tried screaming at your guitar with a few dist. pedals on?).  Other than that, it's possible that the power supplying your amp or pedals is doing something wrong, although doubtful.

I hope I could help, and that I don't mislead you or anything.

-Colin

[Peter Snowberg]

Depending on exactly what type of lights those are, They could easily be the cause of a lot of noise. HID lights come in two basic styles; probe start and pulse start. When pulse start lamps go out, the fixtures will often try relentlessly to ingite them anyway. That involves making 3000-4000 volt spikes to try to ionize the lamp. When probe lamps fail they often sit there arcing all day long. Just imagine each one as a Marconi spark gap transmitter modulated with a 60Hz sine wave.

Either of those will be bad news for your audio. when all the lamps are running, hopefully you will have less hum. I would start there.

Another possibility is that the new building has underground service which just happen to run by the stage area. Hopefully it's just the lighting.

Good luck.

I'm just curious.... You have a Black Cat OD-1 clone, a TS808 clone and a Boss Metal Zone on your pedal board at church?  

-Peter

[ErikMiller]

Yeah, I was wondering about the Metal Zone at church, too. I can dig the TS808, but a Metal Zone?

One thing I can think of to try is checking the mains to make sure that 3rd pin is earthed, and that hot and neutral are where they should be.

I carry a Radio Shack "bug" tester for just such use.

[Jered]

Hi Paul, are the lights on one switch? If multiple switches, try turning of some of the bad transformers and see if your problem becomes less prominent.
 If it is the lights causing your problems, then maybe you can disconect the transformers from the AC volts, if they are not producing any light.
The HID lights are easy, turn off the breaker, undo the four cover screws, undo the two screws holding the shield and socket on the face. Inside you will see a large transformer and a huge capacitor, 10uF/400 V, I discharge these every time I replace one of these transformers, but they don't usually seem to be storing a charge, don't know why. Then just disconect the wire nuts connecting the lamp from the mains. Reconnect the wire nut, individually to each wire, one black(hot), one white(neut),  leave the ground as is.Add a piece of  elec. tape to insure the wire not stays secure and your done.
  Jered

[Paul Perry (Frostwave)]

Yeah, I was wondering about the Metal Zone at church, too. I can dig the TS808, but a Metal Zone?
/quote]
QUOTATION: Why should the Devil have all the good tunes?
ATTRIBUTION: Rowland Hill (1744â€"1833).

Perhaps that should be "tones", not "tunes"!

[Paul Marossy]

Thanks for all the replies! I now have a few more ideas to confirm my theory.

A Metal Zone at church?!? Why not? I attend a church called "Extreme Church" and we like to rock. Actually, I have the Metal Zone EQ'd more like a really hot overdrive with a little bit of mid boost than a scooped mid sound. It's a pretty versatile distortion pedal with that parametric EQ it has. I mainly use it for some nice soaring leads, one or two songs we do lends itself to chord work with it. The other cool thing about it is that I have found a way to get controlled feedback with infinite sustain at low volume levels. Using a wah in conjunction with that allows me frequency control of the feedback, kinda like Satriani's Flying In A Blue Dream tune. Not something I use all the time, but there are times when it fits the musical moment.  

Anyhow, I have all of my pedals set so that the volume level is roughly the same when the effect is on as when it is bypassed. If I want to boost my solo, I step on the volume pedal. The amp I use at church is a Fender Hot Rod DeVille.

I talked to one the guys at the church yesterday who has been an electrician for 25 years. He kind of agrees with me that those lights radiating EMI must be the problem, too. I seem to be acting as some sort of antenna. We are going to try to plug me into the same circuit as the rest of the stage and see how that works. I didn't know on Thursday night at practice that I was on a different circuit as everyone else... He also wants to get a lift and take care of those annoying hummers. The bldg. is pretty large, about 35,000 sq ft with about a 24 foot ceiling, the inside is basically gutted and was in bad shape before we moved into it, but it is getting better with each passing week.  

We are currently using about 6500 sq ft. There is 3 phase and 1 phase power in the bldg. I believe all the lighting is supplied by 110V. I don't think 3 phase power is actually being used as the central plant is currently inoperative, and the chiller or boiler aren't operational.

So, at the next practice, if I'm still having this problem, I will have them turn out the lights and see what happens. I am also going to construct a little power conditioner for my pedal board power supply. I think it makes a slight hum that gets amplified by my DOD FX-17 volume pedal. I'm doing everything that I can to deal with this monster!

[Paul Perry (Frostwave)]

Another test is to try runnig all the fx on battery (temporarily) just to see if it is power supply related. There may be slightly too much load (espexially if your mains are slightly overloaded as well). Some church electricals aren't up to code (volunteer work, but who's going to prosecute a church!!)

[Robin]

I think Paul may be right about the problem being power supply related. From your description it sounds like the "feedback" issue is not microphonic (as in Hendrix or oops guess that mike was on) but rather em/rf trash on the mains. Do you use any kind of power conditioning for your gear? I travel with a cheapy 4-outlet surge protector designed for computers. The cool thing is that it has isolated filter banks and a line fault indicator.

[Paul Marossy]

Yeah, we are using power strips for all of our equipment... I don't know if they are high quality types or not, but they look pretty decent.
I am using a 200mA Boss power supply to power all 10 pieces on my pedal board. I have never had any problems with it so far.  

The other guitar player on the music team doesn't have this problem. I suspect that it is because he plays a Les Paul. They have those metal plates covering the exposed part of the pickups. He uses a POD, too. All of my commercial pedals and the ones I made have never given me any problems with hum or feedback. I play an Ibanez SG470FM (green, mahogany body with flame maple top), which has pretty decent passive pickups in it. I suppose another thing to try is taking my Strat down there and see what happens.

Well, tomorrow is Sunday, so I will see how it goes...  :wink:

[Paul Marossy]

Well, just to update y'all, this morning was a lot better. I had an idea to physically lower my pickups a little bit, so that they are further from the strings, and it actually helped quite a bit with the feedback problem. Still have the problem, but it is occassional and it seems to be at least managable now.  And, plugging my power strip into the same circuit as everyone else seems to have helped somewhat, too.

Unfortunately, I am still getting a hum, but it is not near as severe as it was on Thursday. I also shielded all of my pickup cavities tonight, so that should help somewhat, too.