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

LSchefman

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I use neoprene pads or folded over wraps, in between all my heads and cabs.

I think my mouse pads could be neoprene, but I have no experience to tell, of course.

I use Isoacoustics pucks underneath my studio monitors to kill vibrations and sympathetic resonances; they’re very effective. I was thinking of trying a few sets with my heads at some point, but I keep putting it off because the pucks are expensive, and I don’t have a problem with the PRS amps and tube rattle.

I have used isoacoustics risers with speaker cabs to isolate them and get them off the studio floor, but that’s a different product than the pucks used to isolate a speaker cabinet from a head. Here are the pucks I use with my monitors:

https://www.sweetwater.com/store/detail/IsoPuck--isoacoustics-iso-puck-isolation-puck-for-studio-monitors-and-amps-2-pack?mrkgcl=28&mrkgadid=3319245782&rkg_id=0&campaigntype=dsa&campaign=aaDSA&adgroup=1233692239:DSA - Studio & Recording&placement=google&adpos=1t2&creative=314973838970&device=t&matchtype=b&network=g&gclid=EAIaIQobChMIg-Cc6p-E3wIVUrnACh2FGwYnEAAYAiAAEgJcpPD_BwE
 
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Buck

It feels awesome to be metal in a plastic society
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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.
Thanks for all the info...interesting about the NOS tubes, I had never even thought of that before. Will consider that and definitely install the dampers on new power tubes before I install.
 
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LSchefman

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Thanks for all the info...interesting about the NOS tubes, I had never even thought of that before. Will consider that and definitely install the dampers on new power tubes before I install.

I’m kind of an NOS tube guy ever since my old Two-Rocks came with them and sounded so great. My PRS DG30 also came with NOS, it was one of the ‘first 30’ offered at the PRS Experience that year that came with a special tube complement.

I wound up putting NOS Mullard 12 AX7s and Siemens EL34s in my HXDA, and it sounds wonderful. The Mesa has NOS GE preamp tubes, but still has the Mesa-branded Chinese power tubes. I do plan to replace them, but to be honest, the amp sounds really good now.
 

DreamTheaterRules

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The Mesa has NOS GE preamp tubes, but still has the xyxy-branded Chinese power tubes. I do plan to replace them, but to be honest, the amp sounds really good now.
Remember not to say that out loud. Mesa won't warranty an amp if they find out it had non-Mesa tubes in it. See what I did there for your protection? ^ ;)
 

LSchefman

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Remember not to say that out loud. Mesa won't warranty an amp if they find out it had non-Mesa tubes in it. See what I did there for your protection? ^ ;)

Thanks for looking after me, my friend!

I’ve only got two years left on the warranty, anyway, and with tube amps, I’m good except for blown tubes (I already had to replace a pair of microphonic power tubes, and a rectifier tube that blew).
 

DreamTheaterRules

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Yeah, it’s funny. We know if you had an issue, you could just drop the stock Mesa tubes in it, right? One guy at the Boogie board was going on about his tube swaps and how he felt he’d improved the tone of the Mark V with his new tube cocktail. Then he had an issue. Amp was 2 1/2 years old. It blew a resister and they would not cover it under warranty.
 

Buck

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Remember not to say that out loud. Mesa won't warranty an amp if they find out it had non-Mesa tubes in it. See what I did there for your protection? ^ ;)
My Mesa Mark V:35 I bought used with no original receipt, so no warranty anyways...never experimented with tubes in that one but it's due for a retube in the next 6 months or so also. Gonna have to try out some NOS stuff, although it's my favorite #1 amp, so I'm not sure the tone can be improved upon! I tend to agree, most of the times, when a tube amp goes down, it's related to a fuse or tube, but then again, the Mesa circuit boards are pretty darn complicated looking to say the least! Had 7 or so Mesas over the years and never had a single issue with any of them other than normal maintenance. I'm of the opinion that once you get an amp, if something bad/wonky is going to happen, it usually happens in the first 6 months or so under normal use...especially if it stays in the studio. Time will tell with the MT15 as far as reliability...hopefully no further issues other than the ones I already have with it. Definitely a love/hate relationship with the MT15 for sure...had many a girlfriend like that in the past and ended up marrying one, so we'll see...LOL!
 

DreamTheaterRules

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I'm of the opinion that once you get an amp, if something bad/wonky is going to happen, it usually happens in the first 6 months or so under normal use..
Totally agree. Usually, parts (even good ones) fail quickly, or else they go years without failing.
 

Deli6505

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I finally got mine a couple weeks ago and right away I noticed a crazy hum on the lead channel (with or without the FX loop engaged). No matter what cables or power sources I've tried, the only thing that got rid of it was to place my Decimator II directly next to the MT15 on top of my cab using a very short connector cable and my Line 6 G10 Relay wireless on the opposite side. However, when I put the wireless back on to my pedal board [chain: wireless > tuner > mini wah > tremolo] and from there ran a long cable to the Decimator (still next to the MT15), that stupid hum came back. And even doing a process of elimination in the chain didn't help at all. I finally threw up my hands, said "F-it" and went back to my Kemper. My head is hung low in shame, disappointment and defeat. For now.
 

brokenromeo

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Does it do it with nothing plugged into the amp, only amp and cab? What is the gain set at?
 

shimmilou

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I finally got mine a couple weeks ago and right away I noticed a crazy hum on the lead channel (with or without the FX loop engaged). No matter what cables or power sources I've tried, the only thing that got rid of it was to place my Decimator II directly next to the MT15 on top of my cab using a very short connector cable and my Line 6 G10 Relay wireless on the opposite side. However, when I put the wireless back on to my pedal board [chain: wireless > tuner > mini wah > tremolo] and from there ran a long cable to the Decimator (still next to the MT15), that stupid hum came back. And even doing a process of elimination in the chain didn't help at all. I finally threw up my hands, said "F-it" and went back to my Kemper. My head is hung low in shame, disappointment and defeat. For now.

Are you saying that the hum was gone when you did this? Could be a ground loop somewhere in your chain. Try guitar directly into amp, nothing else plugged in, no effects, no wireless, and if you have no hum, this would indicate that it is not the amp.
 

Tremontinator

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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.

Do you own one yet?
I told my dealer to contact PRS, order me one, and to test it before they shipped it.

I showed him numerous posts in numerous places and made it very clear: This amp is known for problems, and I won't be paying for problems.


I think we played it through 4-5 cabs and then there was a bunch of other guys who tried it before I finally broke him on the price.

I don't like to brag but, I basically bought my MT15 at dealer cost :p
 

Deli6505

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Are you saying that the hum was gone when you did this? Could be a ground loop somewhere in your chain. Try guitar directly into amp, nothing else plugged in, no effects, no wireless, and if you have no hum, this would indicate that it is not the amp.
Well, hooking it up without a noise gate is not an option so the Decimator is a given. I found out that it was a few bad cables causing the issue.
 

Gustavo Posada

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Hi @Tremontinator ! Could you please share results with the following? Thanks!

I've tested on the following conditions: isolated power outlet (240V 50Hz 10A), prs hollowbody ii, gibson les paul custom, parker rf522, subzero 10" cabinet with shielded cable, no effects pedal, no effect loop, no footswitch, Presence Treble Middle Bass Gain at 12' and Master Volume at 9'.

1. When I turn the power on and standby off, I can listen to a hum buzzing to the speaker. Is this an expected behavior? None of my other tube amps reproduce any sound/noise while standby is off; actually, is like a mute switch.

2. When standby is switched there is a "bump" noise that goes to the speaker. I've heard this before on amps and pedals with true-bypass switches that are not working properly; usually a lack of resistance that takes care of the load while switching, like a relay. Is this an expected behavior? I understand the bump noise when the amp is on and the bypass off and change from 15 to 7 watt (or viceversa), but on the standby?!

3. Bias reading is different for both exits, 25.1mV and 27.2mV. If tubes are a match paired, shouldn't the reading be the same? Else, if this can be adjusted there is only one bias adjust knob.

4. Master and Volume pots work like an exponential curve that makes the volume control tricky to manage, shouldn't they be audio taper or linear? Else, this makes no sense on having a blast during the first 1/4 and then just audio compression.
 

Tremontinator

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Exceeding limitations of my knowledge

I'm gonna have to recommend you seek out somebody else, bro. Sorry, dude. I really want to help you but, you're getting way beyond me.


If I was in your shoes, I would most likely contact customer service.



I held off on buying my MT15 for quite some time due to the excessive number of complaints I saw regarding noises.


If you have Facebook, you might look for the MT15 group, and ask them. I was in there from week one, up until I abandoned and deleted my Facebook
 

Future Barbarian

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I just got my PRS MT 15 the other day and the lead channel has a buzz that sounds like an electric bug zapper. Is this a sign of a bad capacitor? From what I know, 60Hz buzz can be sign of a bad tube but this is considerably higher pitched and sounds a lot like a electric bug zapper. This is plugged into a Furman power conditioner or any other outlet in my house. Never heard this sound in previous amps. It definitely gets louder when the MV goes up.
 

Gustavo Posada

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Good morning!
No worries, I have contacted both the seller [Thomann] and PRS Support. I'll make sure to share the answer... if any. I have faith!
I don't have facebook or any other social network; the bits of time that I have available, I devote them to music.
 

Gustavo Posada

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Good morning!
No worries, I have contacted both the seller [Thomann] and PRS Support. I'll make sure to share the answer... if any. I have faith!
I don't have facebook or any other social network; the bits of time that I have available, I devote them to music.

Got back from Thomann

Here are the answers:

Hello Mr. Posada,


thank you very much for your patience.
In this amplifier the standby switch works differently than in other tube amplifiers. The power tubes are under high voltage even when the standby is in "off" position. That´s why small amount of noise is hearable.
The click during switching on or off is also completely normal, there are few amps which doesn’t make any noise by powering on or off.
Good to know: This has nothing to do with true bypass switching on guitar pedals. It is caused by transient voltage spikes in the power supply electrolytic capacitors and although it can be unpleasant, it is safe for speaker and will not cause any damage.
25mV and 27mV means that one tube runs slightly warmer than the other. Although this is still acceptable - there is always some small difference between power tubes. More than 3mV would already be too much.

Kind regards

Sebastian Held, Kundenservice
Tel: +49 9546 9223-68 | Fax: +49 9546 9223-8399 | E-Mail: [email protected]
 

Future Barbarian

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I just got my PRS MT 15 the other day and the lead channel has a buzz that sounds like an electric bug zapper. Is this a sign of a bad capacitor? From what I know, 60Hz buzz can be sign of a bad tube but this is considerably higher pitched and sounds a lot like a electric bug zapper. This is plugged into a Furman power conditioner or any other outlet in my house. Never heard this sound in previous amps. It definitely gets louder when the MV goes up.

I tried playing the amp for a bit and now the bug zapper buzz has infiltrated the clean channel. The amp is completely unusable. I have a replacement MT15 arriving tomorrow so I'll be able to tell if the problem is systemic or isolated to the one amp.
 
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