PRS MT15 and TC Electronics G System


New Member
Sep 21, 2023
Just got my PRS MT15 and I love it! Tone is to die for. However, when hooking up my TC Electronics G System with the 4 cable method I'm having no control over the clean channels volume. It's stuck at full open regardless of where the volume pot is set. G system changes amp channels just fine but when I go to a clean channel setting its always at max clean volume. Red/dirty channel is fine, volume control on amp works fine. If I unplug the G system from the foot control output on the amp and use the pedal that came with the amp, volume works correctly.

I saw the post on the Helix and MT15 but this seems to be a different beast here. Anyone have similar problem or an idea how to fix?
How Does It Respond If You Don't Use 4 Cable Method? Have You Gone Through All Levels/Outputs To Make Sure There Isn't something Odd Going On There In the G System?
The amp works fine just the way it should if I just plug guitar into it with nothing in FX loop and the PRS footswitch. If I plug in my G system to FX loop, because it uses relays to control channels, it's starts doing weird stuff. Using the G System to control channels it works, but like I said, the volume control stops working and is set at max no matter what I do with the volume knob. With G System in the FX loop and the PRS controler, channel switching kind of works. The clean channel will play clean but it will light up red. It's so odd.
The G System shouldn’t have any effect on the channel switching, LED color or otherwise, if the signal is just being run through the G System from the fx loop. Either I’m misunderstanding your problem or there is indeed something very strange going on. How does it behave using the G system in the loop and no foot controller, just the switch on the front of the amp?

I don’t have a bulletproof answer, but maybe this will send you in the right direction - for one, PRS amps run a hot signal in the effects loop, which I think equates to line level, result of the amplification factor of the gain stages in the preamp, so many times more than an “instrument level” signal. As you turn the amp up, the signal sent from the loop gets very high in gain factor - not talking distortion, just straight up amplitude.

Second, the fact that the lead channel has a MV, and where it’s located, is probably why the combination is behaving the way it does. Now, I don’t know where the lead MV is located relative to the loop, but my guess would be after, based on what you’re seeing. Kicks in and reduces volume when the lead channel is engaged, would make sense to me.

Ultimately I suspect maybe your G System is expecting to see an instrument level signal, but I could be wrong. If there are settings for that, maybe try adjusting them. Seems from what I see online that the G System loops are mostly intended for gain pedals to be in them, which would be instrument level signal.

The first line of PRS import amps, the “SE” 20/30/50, had switchable line/instrument level loops, and they were a heck of a lot more user friendly. Not sure why they stopped that feature, it was awesome.
Most digital effects systems will allow you to set the volume level going into the effect box and coming out of the effect box.

You probably already thought of this, but just in case, it might be worth verifying your level settings. I mention it because I couldn't figure out why my H9s were hissing loudly with a new pedalboard, and then I remembered to check the levels. Sure enough, I had forgotten to do it correctly.
I recently purchased the Voodoo Labs PX-8 Loop Switcher and Control Switcher to use with my MT15 and I have to say that these two pieces of gear have really brought out the best of an already awesome amp! I was reading about your dilemma with the clean volume not working correctly and while I am not familiar with the G-System or its capabilities (I wasn't aware that it could also switch channels, too), I had one heck of a time trying to wire this rig up and I had to call Ben over at Voodoo Lab to get it routed the way I wanted. I never had much luck with the 4-cable method and even after Ben explained it to me at great length, it still went way over my 51-year old head so I went and took pictures and re-labeled my main guitar leads so I can recall the correct flow. Now it works like a dream and I cannot imagine the MT15 (or any of my other amps) without these two pieces of essential gear. I wish I had some suggestions for you concerning the G-System. Good luck!
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