Marshall sqeal at high gains...wtf?

[hareek]

Hey all. I tried to search for an answer to my question but I couldn't find one so here I am seeking knowledge from you great ones!. I have a marshall tsl 100. When I play on my lead channel, I get a high pitched feedback when I crank the amp to about 4 and the gain at 9, even if the volume on my guitar is turned all the way down. It doesn't do it on my clean channel. I can't remember if it does this all the time or just when I'm miced and coming back through a monitor at a show. I would test it but my cab isn't with me right now so I thought I'd ask you guys first. So is this normal? Does this have anything to do with being miced? Is it my guitar? Do I need to take my head in to get repaired again?!?!? Thanks in advance!

 

[The Golden Boy]

Re: Marshall sqeal at high gains...wtf?

Does it do this with the lead unplugged?

 

[Farkus]

Re: Marshall sqeal at high gains...wtf?

Could be microphonic squeal. Used to happen to me all the time when I used a 5150 and HS DiMarzio pups. Are you using humbuckers? If so, are they potted? This happened to me alot when trying to use high gain with traditional single coils, as well.

If the amp is NOT doing that when unplugged, try your amp with a guitar equipped with humbuckers and see if it continues.

Hope that helps,
Mark

 

[some_dude]

Re: Marshall sqeal at high gains...wtf?

Turn it up and tap the preamp tubes.....if you hear one that sounds different from the others (it tends to ring afterwards), replace it.

 

[J Moose]

Re: Marshall sqeal at high gains...wtf?

Turn it up and tap the preamp tubes.....if you hear one that sounds different from the others (it tends to ring afterwards), replace it.

Yup.

Tap each tube gently with a screwdriver, pencil...even a pick.

All the tubes are going to make some noise.

A microphonic tube will make LOTS of noise!

 

[kmcguitars]

Re: Marshall sqeal at high gains...wtf?

Most Likely a tube. What kind of repair/mod has the amp had in the past? If you had it modded or the tech who repaired it did something odd? You could have a parasitic oscillation bug lurking around.

 

[34029324079]

Re: Marshall sqeal at high gains...wtf?

I HATE that squeel! Makes me want to say go with EMGs-active.

TSL? When I run through a rig that is not geared up for metal and I have a pedal or I turn up the gain,I run a noisegate in the mix. Might be the pickup not installed correctly also.

 

[Gearjoneser]

Re: Marshall sqeal at high gains...wtf?

If you don't have the spare pre tubes to change them all out, try switching their position in the sockets, and see if the squeal stops. Marshalls are practically indestructible, so problems can usually be traced to a bad tube, bias that has drifted way off, or broken jack.

 

[hareek]

Re: Marshall sqeal at high gains...wtf?

I have 2 lil' 59's in my bridge and neck position and a duckbucker in the middle. When I get my cab tomorrow, I'm going to try to unplug my guitar from the amp and see if that kills it or not. I can't think back far enough to tell if it was doing it before I replaced my single coils or after so I'm just going to have to check it out tomorrow. I'm also going to try to plug in my friend's stock PRS to see what that does.

The head has been taken in to get work done 3 times already. first time was because the reverb wasn't working and they had to resolder a resistor on the circuit board. The second time was just the footswitch. The third time was because of a real nasty hum that the amp was making and it had something to do with the input. Before they diagnosed the input, tech support said it was the preamp tubes but sent me EL 84's(or 34's-whichever the small ones are) by accident. I had my dad try those for me over the phone not realizing we had been sent power tubes instead of pre-amp tubes. The amp did nothing (obviously) with power tubes in the pre-amp spots but went back to normal when the 12AX7's were put back in. No harm seemed to have been done after this huge error! The repair shop did whatever with the input and the hum is gone and the amp sounds fine. The amp is only two years old so the tubes should be fine but I will try tapping them like you said. I'll also try my other pickups because I installed the bridge p'up myself but had a tech do the other two. I'm pretty sure the squeal was there with all the pickups but I will check again.

 

[some_dude]

Re: Marshall sqeal at high gains...wtf?

The amp is only two years old so the tubes should be fine but I will try tapping them like you said.

Age really doesn't have anything to do with microphonics.....I had a microphonic tube in an amp that I bought new.

 

[hareek]

Re: Marshall sqeal at high gains...wtf?

Age really doesn't have anything to do with microphonics.....I had a microphonic tube in an amp that I bought new.

what does microphonic mean?

also someone had mentioned if my pickups were "potted." I'm not sure what the guitar tech did with my middle and neck pickups but I wired my bridge pickup according to the diagram from the SD website. What does "potted" mean?

Also, I dunno if this makes a difference or not but I practice on a solid state Fender Deluxe 112 plus and I can crank that thing and not get the squeal that I get on my marshall which leads me to believe that its not my guitar but I'm still going to try a different guitar on my marshall just to see.

Also when I check my preamp tubes by doing the tapping method, how loud should I crank the amp and should my guitar be plugged in or not?

 

[some_dude]

Re: Marshall sqeal at high gains...wtf?

what does microphonic mean?

Basically there's two types of feedback.....microphonic and harmonic.

Harmonic feedback is the sound you get when the soundwaves off the speakers vibrate the strings on your guitar in a (debatably) musical way.

Microphonic is when the soundwaves do the same thing in a screachy, unmusical way......such as the ear peircing screach you get when a microphone feeds back.

also someone had mentioned if my pickups were "potted." I'm not sure what the guitar tech did with my middle and neck pickups but I wired my bridge pickup according to the diagram from the SD website. What does "potted" mean?

Potted is the process of dunking a pickup in a pot of hot wax. An unpotted pickup has loose coil windings that can vibrate when hit by the soundwaves of the speaker....if there's enough gain going on this'll turn into screachy microphonic feedback.

Also, I dunno if this makes a difference or not but I practice on a solid state Fender Deluxe 112 plus and I can crank that thing and not get the squeal that I get on my marshall which leads me to believe that its not my guitar but I'm still going to try a different guitar on my marshall just to see.

It's probably not your guitar. If those are aftermarket pickups it's more than likely they've been factory potted.

Also when I check my preamp tubes by doing the tapping method, how loud should I crank the amp and should my guitar be plugged in or not?

I'd either leave it unplugged or with the guitar's volume on zero.

Turn it up to your normal playing volume with your normal amount of gain.

 

[AdmiralB]

Re: Marshall sqeal at high gains...wtf?

If it squeals with the guitar volume off, it isn't the guitar or the pickups. It might be the cable but that would be very unlikely. It is most probably a microphonic tube.

 

[hareek]

Re: Marshall sqeal at high gains...wtf?

It's probably not your guitar. If those are aftermarket pickups it's more than likely they've been factory potted.



I'd either leave it unplugged or with the guitar's volume on zero.

Turn it up to your normal playing volume with your normal amount of gain.

They are all aftermarket Seymour Duncan pickups that I bought and installed around last christmas so I guess they are potted. Like I said, the guitar sounds great on any other amp so I think the problem is definitely my marshall because I've also tried different cables.

If it squeals with the guitar volume off, it isn't the guitar or the pickups. It might be the cable but that would be very unlikely. It is most probably a microphonic tube.

I'm really hoping its just a tube because I have a lot of shows with my band coming up and I can't afford to have this thing in the shop again. A bad pre-amp tube is an easy fix and I don't mind spending whatever on a tube if it will fix the problem and keep me from taking it in to the repair place. Thanks everyone for your input. I'll check the tubes tomorrow night and let you know what I find.

 

[Mephis]

Re: Marshall sqeal at high gains...wtf?

Have you checked around the amp to make sure there's no power outlets/electronic equipment near by?

If so try shifting stuff around. I was getting nearly the exact same problem but come to find out it was just my line conditioner. Moving it a foot away fixed it.

 

[hareek]

Re: Marshall sqeal at high gains...wtf?

Have you checked around the amp to make sure there's no power outlets/electronic equipment near by?

If so try shifting stuff around. I was getting nearly the exact same problem but come to find out it was just my line conditioner. Moving it a foot away fixed it.

yeah I've checked all of that already. Its not any type of interference. I wanted to check the tubes tonight but that's not gonna happen cause the guitarist in my band has my cab and he's not answering his phone for some reason so hopefully I can get it tomorrow and post back here what I find.

 

[brit84]

Re: Marshall sqeal at high gains...wtf?

Does it squeal between palm-mutes and such?

if so it sounds like feedback from high gain and volume, i got a boss ns-2 noisegate cause i play with ridiculous amounts of gain and volume. You set it up to cut out the screech and hiss without killing your tone or sustain. best effect pedal (if you call it that) i have ever had. You can also mute everything to switch guitars silently.

 

[That90'sGuy]

Re: Marshall sqeal at high gains...wtf?

Due to the symptoms you're describing, it definitely sounds like a bad tube (probably a bad preamp tube if you're only having an issue with one channel)

 

[hareek]

Re: Marshall sqeal at high gains...wtf?

Ok I have my back plate on my head off and before I tap my preamp tubes, upon first glance the right most tube is leaning to the right and doesn't have a marshall logo on it like the others. also before i start messing around, I pulled a tube out and it looks like they can rotate, lets say 90 degrees and still be able to be pressed back in to place. Is there a certain orientation within the socket these tubes need to sit or does it matter?

 

[Rich_S]

Re: Marshall sqeal at high gains...wtf?

9-pin tubes can't be rotated wrong in their sockets unless you REALLY force something. Look at them closely - the pins are spaced for 10 pins, but there are only 9, plus a blank spot. The blank spot on the tube must line up with the blank spot on the socket.

The first tube falling halfway out might be your problem. Re-seat it, and try to make the squeal.

Then, look for a microphonic tube. Make sure all the tubes are firmly seated in their sockets. Turn the amp up until it squeals. Does it do it with the guitar turned all the way down? If no, then it might be the guitar.

If yes, look to a microphonic tube. Just tap each preamp tube lightly with a pencil or something else non-metallic. The microphonic tube will make a ringing noise, noticeably louder than the others.