Is there a fix yet for the MT15 noise/hum?

LSchefman

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100% agree!! Physics favors entropy.

I’m all about the Second Law of Thermodynamics! :)


“Really, Les? You were so freaked out by physics in high school that you decided to go to law school instead of medical school simply to avoid having to take physics in college.” :rolleyes:

“It’s because I discovered that the antidote to insomnia was a physics book. I couldn’t stay awake for even one chapter. They might as well have given me sedatives. Looking back on it, the discovery of physics books being a safe alternative to sedatives was a brilliant discovery!”

“Did you make use of your ‘brilliant discovery’ later in life?”

“Not really. But later on, I discovered the sleep-inducing qualities of Anton Bruckner’s music. I’ve made good use of that.”

“You listen to Bruckner to fall asleep? Even the 4th?”

“Seriously? Have you listened to the 4th all the way through? Wake me when it’s over.”
 
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kbprs

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FWIW, the Archon FX loop issue regarding radio frequency interference can be fixed with a grid-blocking resistor added to the grid of the FX loop return triode. It's a super-cheap, trivial fix (see pic). This resistor is actually missing from other PRS amps as well, though most likely more noticeable on the Archon due to higher gain levels, etc. I'd be surprised if the MT15 lacked a grid-blocker—just mentioning this because the Archon was discussed.

I've also seen a PRS Custom 50 with a low-level hum issue. My best guess is the proximity of the FX loop tube to the power transformer, varying levels of leakage from power transformers (especially for this CN-made amp, I would presume), and the general design/sensitivity of the loop itself. As people have mentioned, the MT15 will likely be more sensitive than the larger amps with more space between components.

In the end, I'm not sure there's a solution other than tighter controls over the PT specs or a different loop design. I spent many many hours trying to debug a C50 with the low-level hum issue and gave up. Pulling the FX loop tube makes the hum go away, whereas pulling all of the other (non-power and non-PI) tubes had no effect.

PRS-C50-grid-blocker.jpeg
 

JCefalu

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I'm reading more and more about the MT15 hum with nothing plugged in. I returned my first one to the dealer because of this issue and now my second arrived two days ago. It also has the noise although not as bad as my first one. While the amp's tones are amazing, it's not really useable for recording on the clean channel. On the Facebook MT15 group, post after post references the same issue with several others also returning their amps either to dealers or to PRS directly to get fixed. I'm just wondering if there's a known fix at this point before I decide what do next. Thanks.

The MT-15 I have is extremely noisy with or without a guitar “plugged in” and even with the LEAD gain on zero it’s a LOUD hum/buzz. Clean channel is pretty noisy, too. Definitely not a normal level of noise and definitely an issue.
 

Joern Venaas

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I ordered mine in July, still waiting for it. The moment my music store receive it, I`ll test it there and then for noise issues. If I hear the problems, the amp will be returned and look for something else.
 

HANGAR18

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From a MT15 Facebook group posting

Sam Sturgeon

Hey everyone! Had the privilege of doing the factory tour last Thursday for the first time. It’s amazing! So here’s the mt 15 connection: Met Doug Sewell, the mastermind behind the mt 15. He’s an amazing guy and really knowledgeable. He basically told us that he put the contents of the archon (and it’s 5 stages of gain) into a lunch box size amp. The details Tremonti added to the table were aesthetics and the fine tuning of the dials and obviously the fact he wanted an affordable lunch box sized amp. With that said, if you have all those components so close together it MAY create a hum ...not always, though...as they were designed to be further appart so that there was no overlap of interaction between all it’s components. He had a few MT15’s on the bench he was looking at right then - not in a back room forgotten about as some had suggested. They are actively trying to figure out a solution. It was cool to see the guts of that monster amp. He also suggested to reduce noise if it is really bothersome, you can swap the tubes out for 6v6’s (I think is the one he suggested) and this will most likely fix the issue - a hack if you will.
Also it was neat to see the prototype of the MT112 cab. They tried with a red piping just between the cab and the mesh. Tremonti apparently said it looked too much like the bat mobile. Haha. Looks like the shipment of those cabs will be coming in end of August.

So does that mean that PRS put these amps out knowing that the laws of physics were going to play havoc with the design being too small and compact which would result in unwanted hum?
 

elvis

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So does that mean that PRS put these amps out knowing that the laws of physics were going to play havoc with the design being too small and compact which would result in unwanted hum?

I believe it means that they put out their best shot at an amp that we were all screaming for and that was already quite late to market.

Incidentally, the archon also had a noisy loop in the beginning.
 

Buck

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Months later, I still love the sounds out of my MT15, but I'm afraid it's getting used less and less for a couple reasons. First off, I have that hum/hiss issue which is really annoying at lower volumes (and it's getting worse). Makes sense when you think of all that's shoved in that tiny head. Second, the volume jump at low volumes...great for live, but bad for bedroom volume. Last, that rattle/vibration I noted on top of some cabs has gotten worse over the last 7 weeks or so...really becoming an issue and quite noticeable on all of my cabs. Took it apart again and tightened everything down again, reseated tubes and still the vibration/rattle noise persists and keeps getting worse. Too bad cuz I love the sounds out of this little juggernaut...just becoming too many little issues and I find myself playing my Mark V:35 head more and more as a result. I still say that this little beast is still the best bang for the buck on the market for the price...just needs a few tweaks in revision 2.0.
 

Buck

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Can you use a mouse pad type thing between the amp and cab?
I've actually been using a couple hand towels folded up underneath the feet of the amp for a "buffer" to lessen the vibration noise...works somewhat, but doesn't help a lot. Have tried gel type pads too, but still makes noise. I got one of the very first ones, so maybe this issue has been somewhat addressed on the new batches?!?!

Bottom line is if you can handle all the unwanted noises, the actual amp sounds fantastic!
 

brokenromeo

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I've actually been using a couple hand towels folded up underneath the feet of the amp for a "buffer" to lessen the vibration noise...works somewhat, but doesn't help a lot. Have tried gel type pads too, but still makes noise. I got one of the very first ones, so maybe this issue has been somewhat addressed on the new batches?!?!

Bottom line is if you can handle all the unwanted noises, the actual amp sounds fantastic!

Have you tried getting a hold of PRS and giving them a shot at fixing/replacing your amp. Another plus to a small and light amp is it’s easier to ship.
 

Buck

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Have you tried getting a hold of PRS and giving them a shot at fixing/replacing your amp. Another plus to a small and light amp is it’s easier to ship.
I haven't contacted PRS yet, not sure if it's worth it to ship there and back, plus potential parts and labor for a $650 amp. I still use this head quite often as I love the sounds it produces, but went back to my Mesa for main practice and live rig. I've got over 180 hours on this set of tubes, going to swap them out and really go through every nut/bolt/screw that can be tightened and see where that gets me...fingers crossed!
 

Buck

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If there are issues with your amp, I'm sure they will cover it under warranty (other than tube issues)...
All of these issues have been reported by others (or so I've read), so I'm sure there will be a fix to address them eventually. For now, going to swap tubes and do my own maintenance. Truth be told, even with these few small issues, I still love this head to death. Great little firebreather to say the least!
 

Van Noord

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If there are issues with your amp, I'm sure they will cover it under warranty (other than tube issues)...
It's not worth sending the amp back for such a small issue. Other users have done this and been without a replacement for months and months, only to finally receive a new amp and have the same issue.
Just turn the amp up and you won't even notice the slight hum.
 

Boogie

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I read PRS say swapping the 6L6s for 6v6s will help reduce/eliminate the hum.
Solely as a noise reduction method, that doesn’t hold water. The FX loop makes sense since they employ contact switches in the jacks that are notorious for poor connections. Even M/B has had this problem. I’d give PRS a chance to figure it out and correct the problem. And wait for an official response.
 

LSchefman

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Last, that rattle/vibration I noted on top of some cabs has gotten worse over the last 7 weeks or so...really becoming an issue and quite noticeable on all of my cabs. Took it apart again and tightened everything down again, reseated tubes and still the vibration/rattle noise persists and keeps getting worse.

Sounds a lot like power tube rattle, which is caused by the parts inside the tubes rattling against the glass, and is far more prevalent with new-manufacture tubes than NOS. Also, the more the tubes get used, the more they can rattle from vibrations. This can happen with any amp. If you’ve ever heard an incandescent light bulb rattle, it’s the same type of thing.

I had a maddening problem with my Mesa Lone Star 100’s four 6L6 power tubes rattling (it’s a combo), and did everything, including replace the tubes. It was only usable if I disconnected the internal speakers and used an extension cab.

So I finally called Mesa, and was told that’s how it is with new tubes, they can’t source better ones, they’ve tried, there’s no fix, next time buy a head version, tough luck, we feel your pain.

I figured WTF, so I decided to try Eurotubes damping rings to be able to use the Mesa combo with its own speakers. The problem was 100% solved immediately. It was magic. That was at least a year ago, the rattle hasn’t reappeared, and no issues at all with them.

Highly recommended, A pair is ten bucks. Cheap thrills.

https://www.eurotubes.com/store/pc/eurotubes tube damper rings.htm

My PRS amps are heads, I use NOS glass with them, and no issues. I do sit them on foam rubber mouse pads to reduce vibration from the cabs, but that’s just a precaution, since they don’t rattle without the pads. As an aside, the rubber mouse pads are probably a more stable and vibration-absorbing platform than a folded towel, less likely to slide off the cab, etc.
 
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Buck

It feels awesome to be metal in a plastic society
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Sounds a lot like power tube rattle, which is caused by the parts inside the tubes rattling against the glass, and is far more prevalent with new-manufacture tubes than NOS. Also, the more the tubes get used, the more they can rattle from vibrations. This can happen with any amp. If you’ve ever heard an incandescent light bulb rattle, it’s the same type of thing.

I had a maddening problem with my Mesa Lone Star 100’s four 6L6 power tubes rattling (it’s a combo), and did everything, including replace the tubes. It was only usable if I disconnected the internal speakers and used an extension cab.

So I finally called Mesa, and was told that’s how it is with new tubes, they can’t source better ones, they’ve tried, there’s no fix, next time buy a head version, tough luck, we feel your pain.

I figured WTF, so I decided to try Eurotubes damping rings to be able to use the Mesa combo with its own speakers. The problem was 100% solved immediately. It was magic. That was at least a year ago, the rattle hasn’t reappeared, and no issues at all with them.

Highly recommended, A pair is ten bucks. Cheap thrills.

https://www.eurotubes.com/store/pc/eurotubes tube damper rings.htm

My PRS amps are heads, I use NOS glass with them, and no issues. I do sit them on foam rubber mouse pads to reduce vibration from the cabs, but that’s just a precaution, since they don’t rattle without the pads. As an aside, the rubber mouse pads are probably a more stable and vibration-absorbing platform than a folded towel, less likely to slide off the cab, etc.
I have a couple Mesa heads and neither of them has any noise issues whatsoever, so maybe I just got lucky!

I appreciate the hookup for the Eurotubes damper rings...just looked them up and will be ordering some later today!!! May as well put those on the new tubes once I swap them all out...been wanting to try some different tubes anyways to get a little less "sizzle" in the saturation.
 

LSchefman

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I have a couple Mesa heads and neither of them has any noise issues whatsoever, so maybe I just got lucky!

I appreciate the hookup for the Eurotubes damper rings...just looked them up and will be ordering some later today!!! May as well put those on the new tubes once I swap them all out...been wanting to try some different tubes anyways to get a little less "sizzle" in the saturation.

The heads have far fewer noise issues than combos, because in a combo the tubes are right next to the speakers; I usually have bought heads, and of course my PRS amps are heads.

However, I had a few older Mesa high power combos 20-25 years ago and didn’t have problems, but tubes were better then. There are several very informative articles about how tube manufacturers have cut corners on the little parts inside the tubes since the US and Western Europe got out of the tube business.

And of course the machinery that makes them is getting old - most of today’s tube makers bought the machines the old European companies had been using.

This is why all I buy now are NOS tubes made before the 80s. They do sound better, for whatever reason. However, the Mesa has the China-made output tube brand that Mesa offers; I’ve replaced the preamp tubes with NOS, but since I put the damping rings on the Mesa tubes, and they work, I’m waiting til they wear out to replace them with NOS.

A tip with the tube damping rings: Because they have to fit tightly, it’s easier to get them on if you take the tube out of the amp, and then stretch the ring to fit over the tube. I put the damping rings in th middle of my 6L6s; I’m not sure that where you put them makes a difference, since I only tried one spot, but since they work I decided to leave well enough alone and not experiment.
 
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