PRS MT 15: FX Loop Hum Solutions

[Bassman1]

ANOTHER UPDATE:

OK, so I tried the noise gate again in the loop, but this time as the X formation. That didn't solve it either. But, when I ran my attenuator in the loop with short patch cables, that solved it! Sure, if you put your ear right next to the speaker, you can hear maybe a little noise. However, it's faint at best. So, short cables and the 12AU7/ECC82 tube seemed to do the trick.

For playing live, I will run 20 foot instrument cables from my board into the FX loop. That'll probably cause some noise, but nothing I would be concerned about on stage. So, that realm is solved too.

For studio recording, this would really be the last issue to resolve. Namely, how to still use a pedalboard in the loop because one would probably need at least a 10 foot cables each for the send and return. Maybe a buffer pedal could resolve this or perhaps other studio tricks. That is something I am sure can be resolved by the recording engineer or some more head scratching.

 

[silbbu]

You bet! Here's the video.

Thank you for this! It really helped and I don't know if I'm imagining it but it seemed to smooth out that master volume on lower levels. There seems to be more choice between silent and too loud now.

 

[viifox]

Thank you for this! It really helped and I don't know if I'm imagining it but it seemed to smooth out that master volume on lower levels. There seems to be more choice between silent and too loud now.

For sure! I also seemed to notice better volume taper as well.

 

[Arthur Saladino]

I replaced the Fx loop pre amp tube with a 12au7 and dramatically decreased the hum in the loop.. (still a little noise about 2/3rds less)... Im happy I found this forum .. thank you all for your advice

 

[Bassman1]

I replaced the Fx loop pre amp tube with a 12au7 and dramatically decreased the hum in the loop.. (still a little noise about 2/3rds less)... Im happy I found this forum .. thank you all for your advice

1000% agree with this. I use an ISP G string Decimator II run in an X pattern so that the front of the amp and the effects loop run through the noise gate. That kills any other noise. It's dead silent now with a ton of gain, pedals, and volume.

 

[Emperoff]

Most of these issues:
- "my fx loop is noisy"
- "my clean channel sucks"
- "my dirt channel has too much gain/compression"

Can be easily solved with a tube swap.

 

[guitar_player4_2_0]

So glad this thread is here, I just picked up a 12au7 from Sweetwater. I was thinking the noise was coming from the power supply to my EQ pedal in the loop, but I guess this is a common problem. I ordered a jhs little black box also, I’m hoping these two things will help tame the volume a bit for bedroom jamming and lower the noise from the loop a bit. Can’t wait to try it out. Thanks!

 

[Bassman1]

I had the JHS a little while ago for the MT15. It certainly helps use the amp at bedroom levels. Though, it also picked up a lot of noise/interference in certain places in the apartment. It kinda worked like an antenna haha.

I ended up getting a Two Notes captor load box. The attenuator in it worked far better, preserved tone, and also provided the option to go direct into the laptop for recording or jamming with a cab simulator. Not bad!

 

[guitar_player4_2_0]

I had a Bugera PS1 reserved but I got the JHS instead. What I don’t like about the two notes stuff is it appears to not have adjustable attenuation levels. Reading the PS1 manual apparently that only cuts the output in half anyways though. I’ll probably get a Captor X eventually, but for now I’m hoping this does the trick. This amp is crazy loud, had a JCA 50 and a 1st gen 5150 III 50 watt and this seems about as loud as those, and harder to get a quiet volume out of strangely.

 

[Bassman1]

Getting a quieter volume out of it is definitely tough. But, damn is it nice when playing with a drummer !

While you cannot adjust the attenuation on the captor, the -20dB on the amp really works well. I found it far easier to find a usable volume once attenuated on the amp itself.

As for the JHS, or certainly is a good band-aid fix. I noticed some tone suck, but it wasn't terrible. If you're looking for an immediate solution that might not be ideal but gets the job done... The JHS will do that.

 

[Gtan7]

The 12au7 info is gold (or maybe prozac). I returned a MT 15 with deep regrets because of the noise, after many hours googling noise gates, etc. One of the official PRS forum "fixes" was to swap out power tubes and rebias. I think i will buy another one, both channels sounded great and of course there's the blue and red lights

mandatory safety link for 1st time tube rollers: if they're exposed DON'T TOUCH the CAPS

https://robrobinette.com/Tube_Amp_Safety.htm

 

[Emperoff]

You can also swap V1, V2 or V3 for lower gain tubes if you want to make the gain range on the lead channel more useable.

V1 affects the whole amp, V2 and V3 only the lead channel.

 

[50W]

I was expecting the loop issue to be a grounding problem.
Maybe the issue is in that area still, but you can be reduce the effect by putting a low gain tube in for the loop? Am I totally wrong?
Still good that there is a work around!

 

[50W]

So glad this thread is here, I just picked up a 12au7 from Sweetwater. I was thinking the noise was coming from the power supply to my EQ pedal in the loop, but I guess this is a common problem. I ordered a jhs little black box also, I’m hoping these two things will help tame the volume a bit for bedroom jamming and lower the noise from the loop a bit. Can’t wait to try it out. Thanks!

Have you tried changing the tube yet?
With a good result?
Cheers!

 

[50W]

Anyway, I tried this today and it really worked!
I had an old 12AX7 with very low output (probably worn down - don't understand - it makes no noises) put it in and it made all the change I needed.
I have noticed that there can still be a hum but that is if I:
- use a pedal which I know have produced hum in other amps.
- put the pedal in the loop too close to the amp and use poor cables.

So I am really happy that I kept this amp. It has a very special voice, actually something I have been looking for all along I think. And you can play every thing from shiny cleans to honky blues tones and all the way to what I guess it was built for - raw metal. Very cool!

 

[Bassman1]

That real seems to be the big workout around for a lot of folks. The other issue that comes up commonly is the volume pot. If that doesn't bother you, then the amp really is just a gem. I still love mine!

 

[50W]

That real seems to be the big workout around for a lot of folks. The other issue that comes up commonly is the volume pot. If that doesn't bother you, then the amp really is just a gem. I still love mine!

What about the volume pot?
I am not sure I follow. Do you mean it should have been a gain control for clean channel or what? Yes, that would have been great!
But I haven't found any other faults or errors on any volume pots so far. (bought it yesterday)

 

[Emperoff]

What about the volume pot?
I am not sure I follow. Do you mean it should have been a gain control for clean channel or what? Yes, that would have been great!
But I haven't found any other faults or errors on any volume pots so far. (bought it yesterday)

He means the amp is stupidly loud since the master volume pot taper is very abrupt (specially for an amp of this wattage).

 

[50W]

OK, thanks for clarification!
Yes, but I think I can handle it.
Maybe the volume dropped slightly when I changed that tube?

 

[Emperoff]

OK, thanks for clarification!
Yes, but I think I can handle it.
Maybe the volume dropped slightly when I changed that tube?

Maybe, but replace that 12AX7. Completely worn tubes can short and damage components inside the amp. Get a proper low gain replacement that is not worn out. A brand new production preamp tube costs 15$. Don't be cheapo.