Goran Lorencin
New Member
Hi there everybody, well after almost a year of owning the small beast and trying to solve the FX loop (which I still did not fix) this happened ... any ideas as to what is happening here?
I have, swapped, turned and so on ... but the "proof" of normal operation with the bridged FX loop tells me that it must have something to do with the FX loop not being grounded properly or maybe that it has a bad jack plug or that ground somewhere else needs to be redone, all basically minor things, just have to get them fixed. Also measured the buzz freq and it is 50Hz, EU mains freq. It is strange that the buzz started to appear sporadicly, also with the use of the 1/2 power switch, so it just did not dawn on me to check the FX loop loop.Have you checked the tubes?
I have, swapped, turned and so on ... but the "proof" of normal operation with the bridged FX loop tells me that it must have something to do with the FX loop not being grounded properly or maybe that it has a bad jack plug or that ground somewhere else needs to be redone, all basically minor things, just have to get them fixed. Also measured the buzz freq and it is 50Hz, EU mains freq. It is strange that the buzz started to appear sporadicly, also with the use of the 1/2 power switch, so it just did not dawn on me to check the FX loop loop.
I hear you Les, and right you are. But you probably did not read my post about me finding out that when bridging the FX loop all is back to normal and the one where I talked about the PRS Europe being so kind and offering to send the MT15 schematic to a service shop of my choice (in my country, as the one in Germany is still quite far from my place). So I'm getting closer and closer to getting it fixed and maybe even a bit better hopefully, as it would also be great to get rid of the switch pops when turning it on and when using the 1/2 power switch. Looks like I'm learning about tube amps and electronics along the way, which is also a good thing,Often that means a ground loop somewhere in your signal chain. Or...maybe the amp needs to be looked at by PRS. What do I know? Not much.
Hi there Weirdoku,
congrats on your purchase hope it'll give you much pleasure.
........
Take care
Great info, mine had the hum whrn nothing was plugged in the FX loop and was ok when FX loop bridged.Apologies for the double post lol.
Over the weekend I did a bunch of stuff. I pulled all the tubes and put them in one by one and came to the conclusion that the hum appears when the FX loop tube is installed. I put a 5751 tube in the FX loop position and I do notice a drop in hum, it's almost bearable. The 5751 in other positions made no difference to the hum.
I've also opened up the amp and had a look inside. Nothing really stands out for things like bad solder joints or bad caps. All connections and ground points appear solid.
I came across a facebook post in the PRS MT15 group where someone took theirs to an amp guy to fix a FX loop noise issue (images below). The ribbon cable was replaced with a shielded cable and they bridged 2 points on the FX loop board. I've got some shielded cable but I'm not sure if this would solve my hum issue since the hum issue isn't caused by something plugged into the FX loop. I can't imagine the non-shielded ribbon cable from the FX loop board picking up noise causing the hum?