Holy Feedback Batman!!! Need some help/advice/etc

[Josh O]

I've been getting my new guitar room setup and I finally had a chance to jack in and play a bit. First I plugged into my Fender Brownie with it's new Groove Tubes 1x12 cab. What an awesome sound cranked up. I then moved on to my Koch Twintone. I dialed up the gain to about 3/4, had the volume at let's say 3 and holy freakin' howling feedback. I used to play this in my spare bedroom upstairs but never really got past 1 or 2 on the volume knob. I've never heard this amp squeel like that at all until now. I then switched over to my 5150 combo which is a noisy pig all the way and as expected, on the lead channel with gain at 6, the volume at 2, it was howling like a banshee.

So, my Fender had no feedback even when I had the volume at 8. Granted it's only 12 watts and isn't a high gain amp. The 5150 I'm not surprised, it's a noisy pig through and through. I am shocked that the Koch is that uncontrollable with the volume only at 3. I tried two different TCM Taurus guitars, each with different pickups and no change.

Here's the room particulars: 11.5'x10.5', 8' ceilings, sheetrocked and insulated walls and ceiling, three walls are foundation walls (this room is in my basement), one is an internal, tile floor glued right to the concrete pad, majority of the floor is covered with a berber carpet (no carpet pad) to cut down echo and save my bare feet. There is nothing out of the ordinary in this room (standard light bulb type ceiling light, no flourescent, no TV, no cordless phone). My previous room was the same size although on an upstairs floor with all carpet and I had a TV and computer with it and never noticed that howl but like I said, had never really pushed past 2 on the volume knob. I have all three amps and my pedalboard plugged into a Furman power strip.

So, it's not a very big room and I would expect some feedback if I had the gain cranked and started pushing the volume but not as much as I was getting, as soon as I took my hands aways from the strings and or pickups, it was just screaming. It's not like I'm standing 6 inches from my amps, I'm a good three feet away.

What could be causing this? Was I just oblivious to this fact with my Koch? My failing memory wants me to believe that when I tried it in the store a couple of years ago, I pushed the volume on the OD channel but didn't get that horrific feedback. Is is the room construction? Specifically the floor? I've been considering the Auralex GRAMMA, would this help? Or is it just the way it is with the amps?

Almost forgot, my pedalboard wasn't even in the chain, it was guitar right to amp. I'm using a Quantum Oxygen Free 20' cable.

[Josh O]

Here's an update since I had a chance to play a bit more, the Koch is feeding back with the volume at 1 and the gain cracked at 3/4. I even left the room and it still was doing it. I tried to put it atop my Groove Tubes cab to get it off the floor and it didn't help at all, probably proving that the GRAMMA won't fix this problem. Ahhh, help!!!

Do I need some sort of feedback buster? The construction of the room is what it is and can't be changed. Do I have a problem with these amps? Please help, little frustrated here.

I like feedback ala Jimi and EVH when I put my guitar up to the cabinet but this is ridiculous.

[Baba]

Josh, sounds like you're experiencing exactly what a guitar and amp are supposed to do!

There are alot of varying values to the equation, but pretty much, the more gain you use + the closer you are to your amp + the higher the volume will result in feedback, sometimes even if you are holding the strings.

A few things, first off,

1. You can see by your different amps, the numbers on the knobs don't mean squat, there is no set value as far as how loud one amp should be compared to another, they are built differently, so don't look at the numbers so much.

2. Plug your guitar(s) in and keep the amps exactly how they are, then roll the guitar volume knob down, or even off. That should take care of it.

3. If you notice the feedback stops, (on your amp) your volume is up too high or the gain is too high, or both.

4. If you like high gain and high volume, in a relatively small room like that, there's not much you can do, a guitar plugged into an amp will react that way. One option would be to plug a noise gate into the FX loop of the amp, and set it high so it cuts your guitar off quickly if you're not playing it.

The only other alternative you have is to just keep your pinky on the guitar volume to bring it down when you're not playing.

Keep in mind, alot of amps are designed to reach close to full output at lower volume knob settings, so use your ears and don't worry about the volume knob number so much. For example, most Fenders are designed so that you can achieve band level with the volume knob on 2-3, you don't have to turn it up to 6 or 7, etc.
Was that a detailed enough answer? :D

[Josh O]

Rolling the volume off on of the guitar makes it go away. It is rather odd to me anyways that even 20' away, which moved me out of that room, the squeel was there although not as pronounced as one would expect.

Baba, as I feared, that was going to be the answer. I took the amp out of my room to prove to myself it's not the room setup/construction. Even in a large room, it still does it. I'm just a little baffled by the fact the Koch was at 1 and it did it. I know you said not to pay so much attention to the actual number but I can't!;0 Like I said, the gain was only at 3/4! The 5150 forget it, that's a lost cause I just have to deal with. I tried the power soak feature on the Koch (cuts output to 25W) but for some reason, I just don't dig the tone. I like it better at full power. The thoughts of adding a Rocktron Hush or something has crossed my mind but I've been such a picky bastard when it comes to the tone I expect from my amps that I'm afraid to introduce something like this in.

Ahhhhhhhh!!!! What did I expect from a 50W and 65W all tube amp in an 11.5'x10.5'x8' room? I have no feedback problems at all with my little 12W Fender Brown Princeton!:) All the power tube distortion it can give me with no wail, of course, it's not enough distortion!;) Guess I can't have my cake and eat it too ehh? The thought of an attenuator like the Dr. Z Airbrake also has crossed my mind on more than one occasion so I can jack the amps up and keep it at non ear-piericing levels but I've seen pros and cons on every unit about wether it maintained the integrity of the tone or not and don't know what to go with Z, THD, Weber? I'm judging by the fact that I didn't like the Koch Powesoak feature, maybe I won't like any of them!

[Josh O]

One other thing to throw out there. I used the Koch for direct record a few weeks back. It has a direct record out jack which has a speaker simulator and you can silent record with the amp. I had the OD channel cranked to like 5 or 6 with the gain at 3/4 and I was about 2 feet away from the amp and it didn't feedback hardly at all. What gives there?

[Josh O]

Further testing was done with a clearer head today. I relocated the Koch to my original room which was a spare bedroom in the upstairs. Same settings, same feedback. I left the room, the feedback died down some, closed the door, feedback was gone. So at least it proved to me that my new room is not causing the problem and that the feedback does dissipate when moving away from the amp. I guess I'm stuck with the possibilty of an attenuator for the Koch because I really wanted to jack it up and feel the power tube distortion. I can't even get past 1 on the volume knob without it feeding back so it's either attenuate or just live with it quiet. My 5150 forget it, I'll deal with the feedback with that, part of the fun with that amp I guess!:D

[Stratmeister]

I tried my Twintone in a small room with multiple guitars and did not have this problem. Don't overlook the suggestion made earlier, a borderline preamp tube (12AX7) can cause this problem. If it is even slightly microphonic it will make the squealling much worse. Just try some new preamp tubes, 1 at a time, and see what happens...

[Josh O]

I appreciate everyone's suggestions. I think I might have found out some things. One, I hit my owners manual today and low and behold, in the function description section on the gain knob, it states the following: "High GAIN settings may cause squealing and/or excessive hum and noise, due to microphonic guitar pickups and insufficient screening of guitar-circuitry". According to Koch, settings between 10-20 are considered high settings and I had the gain at like 15. This could be a possible "DOH"!!! I also played today and with the gain at 12 and the volume on between 1 and 2, it wasn't too bad. If I left off of the strings, the feedback would eventually build up but it wasn't instant. With the amp set to the clean channel, I had the volume at 4 and 5 and it didn't feedback a bit, it was just too loud for that size room. Since I'm not getting any noise there coupled with what the owner's manual said about high gain, am I pretty much safe on the preamp tube front? I really don't want to spend the money on new tubes for no reason. I think that this further cements Baba's post that it's just the way the amp is.

[Josh O]

Okay, here's the latest:

My Koch has four preamp tubes, one E/H 12AX7EH and three Ruby ECC83/12AX7A. There is no schematic for this amp anywhere so yur guess is as good as mine as to which is the PI tube, etc. The preamp tubes are buried almost out of sight but there is a line of three together, the one E/H and two of the Ruby's and then one Ruby all by itself behind this row. The E/H is the first so I assume this is the V1 position. With the amp on the lead channel, nothing plugged in, the gain at say 15 (out of 20) and the master volume at 4, I tapped each preamp tube with a wood dowel and heard the following through the amp:

The E/H tube (again, most likely V1 from what I can gather) was very loud and almost bell like when I hit it, the other three were rather muffled when I hit them in the same spot with the same amount of force (I wasn't cracking them or anything). I turned the volume up to six and the E/H tube rang even more, it definetely sounded like I was hitting a bell almost. So, is this a sign of a bad tube? I really couldn't get a good look at all of the preamp tubes up close and personal but I could've sworn I didn't see any glow from this tube although the filament wasn't at my best point of view. Did I find my smoking gun? Should all of the tubes sounded exactly the same if all were good? One other thing, the Koch tube layout called for a 7025/12AX7WA in the position where the E/H 12AX7EH tube is. Not sure if the E/H is the stock tube or not. What difference is there between the 12AX7WA and 12AX7EH?

I then moved onto my 5150 combo for the heck of it. I used the same levels and hit each preamp tube and the tube to the very right in the line (looking from the back, again I assume V1) was alot louder than the others when I tapped it. It didn't have that bell like tone but it definetely was louder. This was a Sovtek 12AX7WR.

So, do I have ailing V1 preamp tubes in both amps, the one in the Koch being worse off than the one in the 5150? Do V1 tubes sound louder than rest for a reason other than a possible sign of them being bad?

[Stratmeister]

If the problem goes away when the guitar volume is rolled off, it's a problem with the guitar, not the amp. It's that simple.

This is most likely the cause of the squeal that you're hearing. Certainly a 12AX7 going bad will cause noise, but a high gain amp will exacerbate it. I'm not saying that V1 is necessarily bad so let me explain a few things just for your general knowledge.

First, if they are the original tubes and you don't have any spares you're playing with fire. Break down, spend a few bucks, get a few spares. Newer production tubes are simply not as reliable or long-lived as the older tubes were, and they will fail eventually, hopefully not during a gig. You can get nice 12AX7's from Bob at EUROTUBES.COM or Mike at KCANOSTUBES.COM for like $9-10 each. Also, personally, I wouldn't even go to practice sessions without a spare set of power tubes and a couple of preamp tubes. Once you have a new 12AX7 try it in each position and see if you hear any differences in tone or squealing. Just that simple diagnostic goes a long way to determining where your problem is with any amp with any noise problem.

Next, basically a 12AX7 is a 12AX7. The other letters describe the "version" of the tube and reflect different construction, materials, etc... which could change the tone, but not the operability. In other words, you won't hurt anything by using a 12AX7 with a different suffix.

The phase inverter is typically the 12AX7 closest to the power tubes.

The first gain stage 12AX7 is typically the farthest away from the power tubes so it will be farthest from sources of noise... power tubes, power transformer, etc... that is V1.

Tapping a 12AX7 (I use the eraser end of a pencil) will help you find a noisey tube. Since V1 is the first gain stage, the signal from it passes though additional gain stages (probably). It will almost always be louder than the other 12AX7's when tapped. You'll know if it's bad.

If you tap a 12AX7 and you get squealing, static, or some funky noise that just doesn't sound like a loud tap, it's probably starting to go microphonic. Replace it with a known good tube and tap on that.

A microphonic 12AX7 isn't always trash. You can often get away with moving a microphonic tube to a different socket farther down the signal path and it will still be usable since the signal won't go though as many gain stages. In older Fenders etc... with tube reverb drivers/recovery you can often move it to the recovery socket and have no ill effects.

Suitable substitutions for 12AX7's are 12AT7, 12AU7, and 5751 types. These are lower gain and can be used to tame an amp with too much gain in a stage. You won't hurt anything by replacing a 12AX7 with one of these tubes, they simply have a lower Mu or gain factor. We do this often to get bluesy tones where you don't want preamp distortion from gain, but power tube saturation tone.

I agree, I don't think this is really a bad tube if the squealing goes away when backing off the guitar's volume control. But if your tubes are more than say 2 years old, I would replace them anyway. But that's just me. You can spend a boatload of money on an amp. The signal goes through those tubes, and if they're even questionable will degrad that expensive amp signal. Don't scrimp on tubes, they are THE most critical signal processor in your amp.

[JGraham]

If I left off of the strings, the feedback would eventually build up but it wasn't instant. With the amp set to the clean channel, I had the volume at 4 and 5 and it didn't feedback a bit...
Josh, just to clarify, when you're talking about all this feedback, you are muting all the strings, right?

[Josh O]

JGraham,

No, it's when I was immediately letting off of them. If I muted all of the strings, it would go away as one would expect it to, but what I was experiencing is as soon as I even began to move my hand away, the squeal would build up quickly or already be there with no buildup. I realize that any tube amp will give feedback at high gain if you just walk away from the guitar with the volume wide open and let it build up but what I've been getting is what I felt to be an out of control, runaway type squeal/feedback. Again at a high gain AND high volume, I suppose that's expected. Example: in the recording studio a couple of years back, I had my 5150 combo. It was in another room, I was on a total of 50 feet of guitar cable and I had the gain at 6 and the master volume at 6. As soon as I let my hands away from the strings, the harsh squealing feedback was there immediately, no slow buildup. My situation at home with the Koch is a high gain and what I consider a low volume, between 1 and 2 out of 10 on a 50W amp. At 1, it builds up, at 2 it's there almost immediately (the squeal) I've been playing this amp at home for almost two years at home with the volume barely cracked so I feel like I'm in new territory.

John,

I'm going to show my ignorance on this one so please bear with me, aren't microphonic pickups a sign of a poorly manufactured pickup? Like what you'd find in a cheap import guitar or something? I used to have an Epi LP Standard a few years ago and the biggest complaint I read about it was the stock cheapo pickups were microphonic, causing the guitar to sound crummy. If I'm right on this one, I'm going to say it's not a problem with my guitars. I tried it with all four of my Terry McInturff guitars, each having a variety of different pickups. Two of them have Terry's Zodiac humbucking pickups, one has a combination of Terry's noiseless single coils and a DiMarzio Tone Zone humbucker and the other has Peter Florance Voodoo PAF style humbucking pickups. I guess I'll say that my pickups aren't anymore microphonic than a PRS pickup. Also, Terry puts extra care into properly shielding the control cavity. So I have a problem saying it's a problem with my guitars. Knowing that, would you stil say it's a guitar problem? I also switched between three different cables (Quantum oxygen free, Spectraflex, Horizon) with no change for the better or worse.

I think I'm back to one of the following two options: (1) V1 tube is beginning to go bad and it's not showing it's true colors until the gain is cranked up pretty high or (2) it's the nature of the amp. I'm assuming the same scenario for the 5150 as well.

I did switch the E/H tube out of the V1 position in the Koch with the Sovtek 12AX7WA from the V1 position in my 5150 and the feedback buildup was alot slower on the on volume 1 but was pretty much there at volume 2. The tubes in the Koch are originals, amp is over two years old. Tubes in the 5150 are probably four years old. The 5150 sat dormant off and on for two years, the Koch was used maybe once a week at low volumes. Neither have been gigged, would help if I gigged!! Maybe I should bite the bullet, spend the $100 to replace all of the preamp tubes in both amps.

One other intersting thing of note, I was talking about this problem to a buddy of mine at work who plays out quite often in small clubs. He said how could you ever use that amp if you gigged if it feeds back that quick at volume 1? Interesting question I thought, don't have an answer for him!

p.s., John, I listened to your band's mp3's, you guys sound awesome, although I don't think you use enough effects ;)

[Sherpa]

Hi Josh. I play through a Multitone 50w combo, which has the same hi-gain channel as your Twintone AFAIK. I've never had any squealing, feedback or noise at that below a volume setting of 5 and gain at 12, whether playing through a CU22, Strat or Tele, though I can get it to squeal like a pig at higher volumes ;)

I've been running the same preamp tube configuration as you describe, and retubed the power amp with Koch-branded Ruby Tube El-34B-STRs. Very little noise even on the post-eq/hi-gain channel regardless of venue type and size.
You're in far better hands with John and other more technically-minded forumites here than in mine, so I'll let you all sort it out and just lurk instead of muddying up the waters.. But something seems to be off in your current rig based on what you're experiencing - the Koch amp shouldn't act up like that. I hope you get it sorted out quickly and painlessly.

[Stratmeister]

Sherpa, my experience is basically the same as yours. I have the Twintone and have tried a CU-22, a Strat, and my new McNaught Phoenix Rising. I even sit on top of the amp, beside it, out in the hall (the amp in a small 10x12 bedroom), gain 1/2 to 3/4 up, and volume too loud to stand. No squealing, no feedback, no real noise to speak of. I'm not a high gain player, so I don't care for the tone at all, but no uncontrollable feedback whatsoever.

I'm back to lurking since I can't add anything else to help.:confused: