need help with 5150 fx loop

[Fragle]

hey there,

right now i'm building a rack setup around my 5150, mainly consisting of a morley aby signal splitter and a behringer vamp pro for clean sounds. the idea is to split the signal, one going into the 5150 with both channels set dirty for rhythm/lead sounds, and the other signal going into the vamp set clean and then into the fx return of the 5150, using the fx loop switch of the 5150 footswitch to switch between clean (fx loop engaged) and dirty (fx loop disengaged).
basically, it's working.
however, i'm getting some signal bleedthrough from the 5150 preamp when using the behringer signal. i tried switching the A/B jacks on the morley splitter as i thought it was broken, but it didn't solve the issue.
changing either the behringer volume or the 5150 master volumes didn't change the level of the dirty signal bleeding into the clean sound. it's fairly quiet, but enough to make it sound bad and unusable for clean passages.
switching from lead to rhythm on the 5150 didn't change anything either, although i didn't disengage the crunch switch on the rhythm channel....just had that idea. wondering if i'll get a clean bleedthrough from the 5150 rhythm preamp then?
however, even when unplugging everything and going straight into the 5150 the signal gets slightly weaker/more quiet with the fx loop engaged. this already happened a few times in the past, but didn't bother me as i wasn't using the fx loop anyways. sometimes it works like a charm, though.

IIRC there's some internet talk about broken 5150 fx loops due to dirty jacks. could this be the culprit in my case? i tried (un)plugging the fx send and return several times to "clean" the jacks, but it didn't help.
could it also be a tube issue? if so, which preamp tube is dedicated to the fx loop?

thanks in advance

[DumpyWumpy]

I think it's the nature of your setup...

When you turn on the FX loop with the footswitch, your guitar signal is still giong straight into the 5150 input and running through the preamp section, but with your rig I guess it is supposed to get "lost" when it exits out of the FX send and never comes back since the sound feeding the FX return is from a different source. I have a feeling it's just a matter of not the ENTIRE preamp signal being fed to the FX loop, it seems like there's a tiny piece of the signal from the preamp section that stays in the amp, which would explain why it comes through along with your clean channel. If you didn't have your guitar plugged into the 5150 input obviously this problem would disappear...

What you need to do is figure out a way to isolate the 5150s preamp section, the same way people do using the 4 cable method with the Boss units.

I think I've experienced this same thing before though even using my Boss GT5 using the 4CM. When I put the GT5 into tuner mode, there was still a dirty signal coming out of my cab that was unaffected by the master volume control on the amp. I never experienced it when I set my GT5 up for my clean sounds though, because my guitar signal was going into the GT5 and then into the FX return of the amp, bypassing the preamp section completely.

There's still a way to do it with your setup but it involves more tap dancing than you'd probably like... If you had the splitter set up for A/B switching, you could switch it to feed the V-Amp only when you were playing clean and feed only the 5150 for distortion sounds, but every time you switched you'd also have to hit the FX Loop switch on the 5150 footswitch...

Have you looked at the Boss LS-2 Line Selector? It's only $80 brand new and I'm positive that it will work for this application.

Guitar > LS-2 Input
LS-2 Send 1 > 5150 input
5150 FX Send > LS-2 Return 1
LS-2 Send 2 > V-Amp input
V-Amp output > LS-2 Return 2
LS-2 output > 5150 FX Return

Then you make sure the FX loop is turned on on the 5150 at all times, and you just A/B between your clean and dirty sounds with the Boss pedal.