MT15 Hiss Issue

[21Hemispheres12]

I’ve had my MT15 since 2019 when I bought it new and haven’t had any issues until now. Over the last week or so I noticed that the drive channel sounds like a waterfall of hiss as soon as the volume is turned up to 8 o’clock and gets more intense the higher it goes. If I plug a guitar into it I just get instant feedback unless the volume is almost off. The clean channel is completely fine so definitely just an issue with the drive side.

I’m going to try swapping around pre amp tubes tonight but wanted to see if anyone had any other ideas.

 

[Bogner]

Most tube amp issues are fuses and tubes. Clearly your fuses are fine so I would begin with tubes. My money says that will solve the problem.

 

[21Hemispheres12]

Most tube amp issues are fuses and tubes. Clearly your fuses are fine so I would begin with tubes. My money says that will solve the problem.

Well I swapped out each pre amp tube one at a time and no change. I reached out to PRS support so l’ll wait and see what they say.

 

[Bogner]

Well I swapped out each pre amp tube one at a time and no change. I reached out to PRS support so l’ll wait and see what they say.

Has anything else changed in your rig recently or been added to it, etc? Cables, pedals, anything electrical/electronics? Do you have any other spare tubes you could throw in the pre amp section? I trust your power tubes are fine and all working as they should be?

 

[21Hemispheres12]

Has anything else changed in your rig recently or been added to it, etc? Cables, pedals, anything electrical/electronics? Do you have any other spare tubes you could throw in the pre amp section? I trust your power tubes are fine and all working as they should be?

No nothings changed cable wise. I have two speaker cables so I tried both of those and got the same thing. I have a spare pre amp tube so I tried that in each position and nothing changed there either. Here’s a video of what it’s doing.

 

[Bogner]

No nothings changed cable wise. I have two speaker cables so I tried both of those and got the same thing. I have a spare pre amp tube so I tried that in each position and nothing changed there either. Here’s a video of what it’s doing.

When you have tried different Pre tubes are you only pulling one tube or are you pulling all of them and mixing them up? I would need to see what tube positions do what aside from V1 and I don't have the tube layout diagram. I will search for it and see the layout. I would check and see if rotating around all pre tubes does anything different at all. Do you have a noise gate and have you played through the amp as it is now? How well doe the noise gate work in this instance if you have one? Does the amp sound or feel/respond any different aside from the noise in any way? Does the noise increase as the amp heats up?

 

[21Hemispheres12]

When you have tried different Pre tubes are you only pulling one tube or are you pulling all of them and mixing them up? I would need to see what tube positions do what aside from V1 and I don't have the tube layout diagram. I will search for it and see the layout. I would check and see if rotating around all pre tubes does anything different at all. Do you have a noise gate and have you played through the amp as it is now? How well doe the noise gate work in this instance if you have one? Does the amp sound or feel/respond any different aside from the noise in any way? Does the noise increase as the amp heats up?

I took my spare pre amp tube and replaced it in each position one at a time. I haven’t tried mixing them up so I’ll give that a shot tonight. No noise gate as I’ve never needed one before and the amp still sounds fine to me. The only difference is I can’t turn the volume up very much without getting a lot of feedback. I don’t think the noise is getting any worse as it heats up either.

I took off the bottom panel last night and I didn’t notice anything burnt or lose so I’m pretty stumped as to what happened. I really appreciate all your help!

 

[Bogner]

I took my spare pre amp tube and replaced it in each position one at a time. I have tried mixing them up so I’ll give that a shot tonight. No noise gate as I’ve never needed one before and the amp still sounds fine to me. The only difference is I can’t turn the volume up very much without getting a lot of feedback. I don’t think the noise is getting any worse as it heats up either.

I took off the bottom panel last night and I didn’t notice anything burnt or lose so I’m pretty stumped as to what happened. I really appreciate all your help!

Please let me know what you find, I will do my best to help you!

 

[Bogner]

I am guessing the OP either found the solution and is playing and making up for lost time or he electrocuted himself.

 

[21Hemispheres12]

I am guessing the OP either found the solution and is playing and making up for lost time or he electrocuted himself.

Good guesses but unfortunately no and also luckily no. I’ve been going back and forth with PTC and am shipping it back for them to take a look at today. They suspect there’s an issue with the pre amp somewhere so I’ll report back with what they find.

 

[Bogner]

Sorry we couldn't sort it. Hope fully it gets sorted in a short amount of time so you can get back to playing it.

 

[21Hemispheres12]

Sorry we couldn't sort it. Hope fully it gets sorted in a short amount of time so you can get back to playing it.

I really appreciate all of your trouble shooting tips! Luckily I have my Helix to hold me over until it gets back.

 

[Bogner]

I really appreciate all of your trouble shooting tips! Luckily I have my Helix to hold me over until it gets back.

Ahh sweet! Glad you aren't without amp of some kind. Sorry we couldn't get you sorted but hopefully it comes back in full force and sounds and feels excellent. Let me know please!

 

[Goran Lorencin]

No nothings changed cable wise. I have two speaker cables so I tried both of those and got the same thing. I have a spare pre amp tube so I tried that in each position and nothing changed there either. Here’s a video of what it’s doing.

Well ... to me it almost sounds normal - looking at the knob settings you got there. It is a power amp. The master position at 9 o'clock is plenty loud, I never play that loud when practising with the band as they can not hear themselves.
You must know that the master volume knob is the biggest issue here hahaha we all wish it would be more gradual, instead it goes from 0 to 50% it the first few degrees of turning it, later, after 12 o'clock it does not ad more volume but rather more "spread", kinda like the gain knob, after 12 o'clock it ads more graininess than real distortion.
What you proved in your video is that this is a very good amp, the clean channel is also very good. Remember that this is MT15 - Mark Tremonti ... he goes chuggah, chuggah a lot. But you can dial in just a tiny bit of gain and it will sound very different.
Another thing, I use a noise gate if I go for the hard stuff. Love the little beast, even though it might not be the best out there it has much to offer for the price. Hope you get it back how you wished it would be, but I think there is not much that can be done here. Will try to replicate your setting next time I play it.

-------------------

Addendum: my 9 o'clock is much louder than usual as I replaced the knobs and my 0/silent is at 6 o'clock. So regarding my statement above ... it's cow dung, I have a hunch of how loud the master volume was set but I can not really compare it to my amp.

 

[21Hemispheres12]

Well ... to me it almost sounds normal - looking at the knob settings you got there. It is a power amp. The master position at 9 o'clock is plenty loud, I never play that loud when practising with the band as they can not hear themselves.
You must know that the master volume knob is the biggest issue here hahaha we all wish it would be more gradual, instead it goes from 0 to 50% it the first few degrees of turning it, later, after 12 o'clock it does not ad more volume but rather more "spread", kinda like the gain knob, after 12 o'clock it ads more graininess than real distortion.
What you proved in your video is that this is a very good amp, the clean channel is also very good. Remember that this is MT15 - Mark Tremonti ... he goes chuggah, chuggah a lot. But you can dial in just a tiny bit of gain and it will sound very different.
Another thing, I use a noise gate if I go for the hard stuff. Love the little beast, even though it is not the best out there it has so much to offer. Hope you get it back how you wished it would be, but I think there is not much that can be done here. Will try to replicate your setting next time I play it.

I got the amp back but have had a chance to fire it up yet. PTC said they replaced some noisy tubes and a few other components and the noise was within their tolerance now. I know something happened because I was using the same settings that worked fine one day and then the next I would get uncontrollable feedback on the gain channel with the gain at noon at any volume.

I’m hoping to try it out tonight so we’ll see how much quieter they were able to make it.

 

[Goran Lorencin]

I got the amp back but have had a chance to fire it up yet. PTC said they replaced some noisy tubes and a few other components and the noise was within their tolerance now. I know something happened because I was using the same settings that worked fine one day and then the next I would get uncontrollable feedback on the gain channel with the gain at noon at any volume.

I’m hoping to try it out tonight so we’ll see how much quieter they were able to make it.

True, could be a bad tube or some small internal solder glitch etc., but from what I've heard I think it is not so bad. Have you tried the 1/2 power switch to see if anything changes? Have you tried bridging the fx loop? Also do you use the right impedance output and cab input? Just wondering.

 

[21Hemispheres12]

1/2 power switch didn’t make a difference and PTC had me try going directly in to the send return and that also didn’t make a difference. I’m using the 8 ohm tap into an 8 ohm Celestion lead 80 so all good there too. I’ve had the amp since 2019 so I was pretty used to it’s sound levels and this definitely seemed excessive from what I was used to.

 

[Goran Lorencin]

1/2 power switch didn’t make a difference and PTC had me try going directly in to the send return and that also didn’t make a difference. I’m using the 8 ohm tap into an 8 ohm Celestion lead 80 so all good there too. I’ve had the amp since 2019 so I was pretty used to it’s sound levels and this definitely seemed excessive from what I was used to.

Well in that case let's hope it comes back sounding the way it did in the good old days ... fingers crossed. Let us know what was the issue.

 

[21Hemispheres12]

Well in that case let's hope it comes back sounding the way it did in the good old days ... fingers crossed. Let us know what was the issue.

Amp is definitely more quiet now. I couldn’t turn it up too much but it didn’t give me any uncontrollable feedback so I’d say it’s fixed!

 

[Bogner]

Amp is definitely more quiet now. I couldn’t turn it up too much but it didn’t give me any uncontrollable feedback so I’d say it’s fixed!

What did they specifically replace or did they not tell you? What tubes are in it now? 5881's or 6L6?