Anti Feed Back "Solutions" for amplified harmonica from a Moon Cat named Jason Ricci
Unfortunately there is no real easy answer to this problem but there are a lot of things you can do to get louder with less feedback and hopefully good tone. I have played in a lot of bands (un mic'ed and miced) that can get real loud at certain times of the night (New Blood, Johnny Winter, Walter Trout and The Bad Kind) and have some experience with combating this issue. After 20 years of touring all over the world, 250-300 days of year, from meth riddled, crappy sports bars and ego explosive open mic to the Paradiso and the Rock and Roll Hall of Fame here are a few tips I've learned and reviews of all the boxes out there that attempt to help you deal with the dreaded feed back issue. First if you wan't to be louder the easiest solution will always be a bigger, louder amp or a direct to PA alternative, having said that here's what you can do you your big amp once you get it. Greg Huemann of Blows Me Away Productions has wrote some great stuff on Volume vs. Gain, revisiting his articles on that and some of this article alludes to those points he makes in my own words.
1.) EQ'ing your rig: Turn all your tone controls down/off. Turn your volume all the way up until your amp begins feeding back (some amps will not engage any volume with all the tone controls off, so you may have to inch one or all of them up a just a sliver). Try playing with Only the volume up really loud. Once you have the amp beyond it's feed back threshold lower the volume a bit you may be surprised how great your tone sounds all of a sudden JUST with the volume knob up! This is because there are Bass, Treble and Mid frequencies in volume when your amp starts working hard. There is an actual reason so many players like to play loud besides just ego. Once your amp is as loud as it can go with only the volume knob engaged then begin to add treble, bass and mids to taste. As you do this you will notice your amp will get closer to feeding back again or will feed back. This is because your tone controls actually add volume or volume of certain frequencies that can feed back just like your volume knob adds TONE! So you will have to back off the volume each time you add more Treble, Bass, Mids etc. Already you will find that your amp is now significantly louder than ever before with just the tone controls backed down and the volume higher a lot of you will like the way it sounds better too at your new much louder, mostly feed back free volume! Imagine where it reads Volume on your amp it also had this: (Treble, Bass, Mids) and where it says Treble , Bass or Mids it also said (Volume).
2.) Stomp Boxes/outboard devices: Here we go! OK... there is and most likely will never be built the perfect answer to our problem in the form of an electronic "solution" that eliminates feedback AND satisfies everyone's needs. That is unfortunately a pretty reliable predication I'm afraid. Part of the problem is "good tone"/ break up,/distortion/compression etc ARRIVE at or beyond the edge of feedback. Feed back is the sound of a microphone or a pick up, picking up the sound of itself so any time an amp is loud this can happen. Here is my run down on my experience with the devices currently available in todays harmonica market. There are really three ways to fight feed back: 1.) Volume gate. 2.) Eq'ing and/or frequency gating/isolations. 3.) Signal Padding. I will now begin with my best assessment of the positive and negative element of these boxes. One of these boxes will work well for you especially IF you did my "volume up EQ down" trick above.
Out Board Pedals/Boxes
A.) The Lone Wolf "Harp Shield" (GATE) : This pedal is essentially a GATE. It attempts to cut off your signal once it detects there is no longer a signal being made by you. This way as soon as you stop playing it essentially tries to mute your microphone and not allow the mic to pick up the sound of your amp. The Lone Wolf Harp Shield has a "sensitivity knob" (the only knob) that allows you to adjust the how sensitive the gate is. If you play kinda hard (most hard players don't even think they do) this pedal will be really easy for you to get your amp REALLY loud with almost NO issues and you'll love it! If you don't play that loud and/or play with a ton of sensitive, subtle, vibrato and other light breath patterns you will have to turn the sensitivity knob all the way down or nearly all the way down so the pedal does not CUT OFF/GATE your notes. Soft/light players will notice that this pedal will attempt to gate frequently when they are playing softly or playing with a very soft vibrato. This is of course a big draw back to the "gate" solution to feed back for many of us and the only problem at that with the Lone Wolf option. The higher you turn this pedal up the louder you can make your amp but the less lightly you can play your harmonica. The plus side/benefit to choosing the Lone Wolf "Harp Shield" pedal is that the Harp Shield does NOTHING to your existing tone, repeat NOTHING and is a PURE feed back eliminating device that is a serious candidate for a type of "solution". Again there is no "Solution" that doesn't eventually create a new issue thats why I'm putting that word in quotes. This pedal retails for 140.00 from some pretty great people in small town Hammond Louisiana. Often you can find all these devices used and now cheaper, from players that didn't take the time to understand what and how the device really works or din't bother doing so basic EQ'ing prior to using plugging in or insist on using a tiny 3-20 watt amp and complaining rather than getting a real rig. Also you may have found one used for cheap from someone who has found another "Solution"...Personally I now have been using the "Harp Shield" for nearly 6 years and is the current and most effective "solution" (that I prefer) that I have found to date. People disagree with me and unless they site the soft volume/gating reason as a disagreement I tend to think they really haven't tried this thing long enough as it's works quite well.
B.) The Kinder "AFB" = anti. feed. back. (GATE/FREQUENCY GATE/DISTORTION): This device is made by mad scientist John Kinder in California and the circuitry can actually be found built in to the chassy/head of the "Harp King" Amplifiers that this supplier also produces which are used by Rod Piazza and Dennis Gruenling, so now you know those guys are using at least A "pedal". The Kinder "AFB" gives you the control to find the particular, offending/feeding back frequencies your self and dial them back sort of like a "soft" EQ pedal thus reducing feedback. The knobs on the far left and right control and I suspect GATE high and low frequencies and are pretty damn effective at giving you a good solid notch of extra volume before feedback, again, especially if you did my EQ trick I listed as the first "Solution" to your battle. Like the Lone Wolf "Harp Shield" if this pedal is turned up too much and you play softly you will hear the gate and it will annoy you but it is not as bad as the L.W. option for that particular draw back. The knob in the middle adds break up/distortion and a little compression as well rounding out your tone and giving you "that sound you were looking for" with volume. Unfortunately for many this is ALSO another problem! While MANY people will ENJOY the way the Kinder "AFB" changes their tone, many people will DISLIKE it as well. This pedal DOES change your tone dramatically and if you do not like the sound of solid state amplifiers you may not like this pedal at all because it uses solid state circuity and that can make your amp sound a little "false" especially if you crank that middle knob. Again a ton of people love and even depend on the way this pedal changes their tone. Another draw back of this pedal is it cannot be plugged in to the wall or a power supply without modification. The modification is simple to do by anyone. Simply obtain male connectors that will attach two female 9 volt receptor thingies (you know where the batteries go) and run them to a Wall worts or two isolated power jacks on a power supply. A "1 spot" is not isolated and will not work. After you have done that you can file or cut a hole for which they can easily exit the device by hand with a file or with a dremmel. Be sure your cut is sanded or buffered with tape so that you don't eventually cut the wires. Another draw back of the Kinder "AFB" is that it can be hard to obtain! There is a waiting list. John doesn't always answer his phone or emails. Sometimes these boxes are built and ready to ship but I personally had to send the money (pedal retails at 359.00) and wait in silence (which I did) up to four months or maybe more for the "AFB to arrive. I have not yet heard of one scenario in which someone did not get their order. John is a good guy I have been to his house and bought a few of these devices over the years but this one will take some trust on your part. Personally I used this pedal for 9 years straight and at one time owned three. It is a very great pedal however I feel I "grew" out of it's distinct and quite fixed sound. I now combine use of the following Lone Wolf products: 1.) "Harp Shield" and the 2.) "Harp Break" and 3.) my signature "Flat Cat" compressor to fight feed back, tone shape and compress in a manner that can change, be tweaked and adjusted drastically or in microbes and as my tastes tend to change from room to room, band to band, song to song, session to session and year to year.
C. The "Squeal Killer" (PAD): Jason Lockwood, the man who makes this is a super nice guy and I hate to write anything negative about this product but I simply still, despite a personal visit to my home do not understand why a simple tube swap on the amp itself wouldn't do the same thing without cluttering up the stage or top of your amp. The Box uses a lower gain power tube (12 at7) to give your amp (with 12 ax7's) more headroom allowing you to turn the amp up louder. The issues with this OR tube swapping in general is that like I said earlier "good tone" comes at the edge of feed back. So you may now have more volume/headroom but now your wanting more "tone" so your amp will still feed back just before it's where you want it to be but you'll be heard louder... so up to you...This could be a good option for the traveling player if you have to use someone else's amp/backline and obviously you don't wan't to swap tubes at a festival, club date etc....which would be rude and time consuming. The Box requires a battery or external power (one OR the other) and retails around 250.00+. Please remember these are my opinions only and allegedly Rick Estrin and Aki Kumar both sometimes use this pedal.
D.) The Lone Wolf "Mojo Pad" (PAD) : Essentially this cute, simple, unpretentious little box is the same thing as the Squeal Killer as I understand it. "The Mojo Pad" uses a simple pad treatment to your signal with a resistor instead of a tube. The Mojo Pad like the Squeal Killer is designed to be used at the end of your chain or before the amp for Pedal/box and cannot be used before a pedal effectively and retails humbly at 49.00 and requires NO power. Personally I don't Pad my amps. I use 5751 preamp tubes.
Here are a few other important helpful tips for fighting feed back to try and think about.
1.) Again get a louder amp that moves more wind with more watts.
2.) Try a newer microphone like a Shure 57, some amazing technology has happened since the 40's and part of that technology was developing mics that feed back less. With todays out board pedals, tube choices etc you can replace that "Bullet" distortion/hotness and get any amount of compression distortion etc that you want out of your rig and/or with a pedal. It's really that simple. You don't see many guitar players searching for old antiquated pick ups to get distortion and compression, they use a pedal with a big amp or a smaller amp mic'ed up. Pat Ramsey used smaller amps but always complained about the soundmen not getting his monitor right or re EQ'ing his tone.
3.) Use a volume control and learn to use it as part of your playing. I don't set and forget these things. I ride these knobs, almost compulsively when I play and this can be seen in 1000's of videos on youtube. You can also watch guitar players do the same thing.
4.) Experiment with raising your amp up on a milk crate or even just off the stage a few inches with something .I use to leave my amp in it's road case wheels. I no longer have a road case. Certain stages act like amps themselves! Many Stages, and rooms will boost and surprise certain frequencies and cause your tone to be completely different room to room! Raising the amp off the stage not only helps you hear better, so you don't have to turn up but also reduces extra bass frequencies (and other undesirable effects) that can be caused by hollow stages.
5.) Move your amp far away from you. This can be bad and good. The good part is it's way harder to feed back, the bad part is you may have to make it louder to hear. However having your amp right under your legs behind you IS NOT a good way to judge volume at all! The amp will be way louder than you THINK it is and you may end up yelling at people to turn down who are less loud than you. This is another reason you would want to raise your amp up or tilt it back and you will see me, Kim Wilson and a lot of other pros also raising the amp up near us when were close to it.
Hope that helped.
Jason Ricci mooncat.org