PRS MT 15: FX Loop Hum Solutions

[Motegi]

It’s been a bad year financially. Been through a couple jobs and sold most of my gear. I’ve had a bunch of amps over the years and the MT-15 was def one of my favorites, not even considering the price. I’m really hoping the MT-100 is import and under 2k, because I really want one. I just hope they work out the loop noise a bit better.

Sorry to hear that man. Hope things start looking up for you!

 

[Bandersnatch]

It's so interesting that people are having the fx loop be the cause of the noise. When I took mine back to the dealer over how loud the noise on mine is, after they talked with the PRS rep, I was told it's basically because they have the 50w archon preamp circuit design and didn't space the components out enough to prevent them from spilling a bunch of electromagnetic noise into each other.

Now mind you, I'm running mine through a Fender Bassbreaker 112 which is a cheap and noisy can for such a high gain head. When I tried mine through the matching PRS cabinet, it was way less noisy so cab components definitely have an effect. I should really try mine in my Orange 212 to see how noisy that one is.

 

[rbdoggface]

I did the 12AU7 swap yesterday and it helped a little. Went from a VERY annoying hum to a mildly annoying hum. Then I tried some other tips PRS support told me to try- use shorter cables with no right angles and secure them together (ziptie, velcro) to limit interference. The cable change made a big difference. I am going to get cables as short as possible and better quality than the Amazon specials I have now. With these changes, it is no worse than the hum you get out of many high gain amps turned up.

 

[Emperoff]

I did the 12AU7 swap yesterday and it helped a little. Went from a VERY annoying hum to a mildly annoying hum. Then I tried some other tips PRS support told me to try- use shorter cables with no right angles and secure them together (ziptie, velcro) to limit interference. The cable change made a big difference. I am going to get cables as short as possible and better quality than the Amazon specials I have now. With these changes, it is no worse than the hum you get out of many high gain amps turned up.

Ok, so the solution is not being able to use long cables? Excuse me but that is lame as fuck. Why not fix the issue everyone has been complaining about since the amp was released instead?

There are a fuckton of lunchbox-style amps and this is the only one with this issue.

 

[rbdoggface]

Ok, so the solution is not being able to use long cables? Excuse me but that is lame as fuck. Why not fix the issue everyone has been complaining about since the amp was released instead?

There are a fuckton of lunchbox-style amps and this is the only one with this issue.

I don't disagree. Unfortunately there are too many products these days with the same types of "workarounds" straight out of the box. I am sure there is a factory level solution to the problem.

 

[MatrixClaw]

Granted, I don't use the FX loop much, but I plugged a delay into mine this afternoon and it's dead silent with the stock tubes

 

[rbdoggface]

Granted, I don't use the FX loop much, but I plugged a delay into mine this afternoon and it's dead silent with the stock tubes

I know. I hate being one of the people that has the bad luck. I’m tired of dealing with it with so many electronics. Guitar amps, computers, TVs. Why are so many manufacturers oblivious to problems so many users of their products have? PRS do say that I could send it in because it is under warranty. But I have read of other people who got replacements that had same issue. Been there done that with other products.
The thing with this amp is- I really like it and the loop is the only issue. Honestly, I have never had an ear good enough to notice the difference in pedals in the loop versus all through the front, anyway.

 

[Motegi]

I know. I hate being one of the people that has the bad luck. I’m tired of dealing with it with so many electronics. Guitar amps, computers, TVs. Why are so many manufacturers oblivious to problems so many users of their products have? PRS do say that I could send it in because it is under warranty. But I have read of other people who got replacements that had same issue. Been there done that with other products.
The thing with this amp is- I really like it and the loop is the only issue. Honestly, I have never had an ear good enough to notice the difference in pedals in the loop versus all through the front, anyway.

I can tell a big difference with just a delay before the loop vs in the loop on the dirty channel. It’s almost unusable in front as it seems to create this washy echo effect. Before the clean channel everything is good.

 

[rbdoggface]

So I tried a different tube swap that was recommended in another group. Put the 12AU7 in the phase inverter slot. Problem is pretty much gone now.

 

[profwoot]

Can confirm that the fx loop hum is reduced quite a bit more by changing out the phase inverter tube (V6) than the fx loop tube (V5). I don't know enough to speculate why that would be.