Marshall tsl fx loop bleed - help needed!

[maejima]

Hi there. I 'm new to this forum and i have a problem that many people seem to have.
I've searched everything on the net and could not find the right thing to do.
I Have a Marshall TSL60 Head made in 2006, the amp plays really well and i had no problems with it at all. The only problem is that now i bought a delay pedal to use in the loop and it just seems useless.

There is as i found out a signal bleed from my main channels to the fx loop and from my FX loop to the output. When i use the delay with the clean channel and i turn the loop off with the footswitch and turn the fx mix knob all the way back the is a slight echo heard through the amp , the problem gets bigger with the crunch and unbearable in the Lead channel. The only fix for the echo to stop is to turn off the delay pedal. The other bigger problem is that when i tried to use the delay and a boost pedal after that in the loop to create a solo sound in the lead channel it immediately starts to feedback like crazy (because i supect of the signal bleed crating a feedback loop) making it unusable.

Some guy suggested the whole fx loop circuit to be moved to a less "noisy" enviroment in the amp chassis , another one suggested that the loop so be made Serial instead of parallel but i haven't found out how to do either of these mods.
Does anyone know of a solution to this problem? Is this a crosstalk problem because the cables run together? What should i do?

[maejima]

So nobody has the same problem? Nobody knows about a solution?
anyone?

[Jazz P Bass]

From the TSL60 Manual:
"USING EFFECTS SYSTEMS
Your TSL combo amp is fitted with a parallel FX
Loop, this is placed after the gain and distortion
parts of the preamp and is the ideal place for
inserting time varying effects, such as delay,
digital reverb, chorus, pitch shifting, etc. By being
a parallel loop, this means that the direct signal is
kept within the TSL’s circuit and therefore your
tone is not degraded by sending it outside the amp.
To use the loop connect your effects processor
(rack type units are better at this job) as described
earlier, turn the effects units direct signal path off
(the FX units manual will tell you how to do this),
set up the unit to give you the effect you require
and then balance your direct sound and effected
sound using the FX MIX control on the front of
your amp. Easy!
Floor type effects stomp boxes are designed to
work in between a guitar and the input of an amp
and should not be used in a parallel loop,
otherwise some very weird and undesired effects
could occur. For their best use, use them where
they are designed to go."
So I think the boost pedal in the loop is not a good idea, which you have found out.
I do not understand the statement about " turn the effects units direct signal path off
(the FX units manual will tell you how to do this)"
There are pad switches for the loop.
Do they help at all?

[maejima]

I 've allready read the manual and i know how a parallel loop should work (my delay's blend knob is maxed giving only the wet signal out). But the problem is that there seems to be a serious amount of crosstalk (signal bleed) between the channels and the fx loop. So the loop signal bleeds to the lead channel and then goes back into the fx loop creating a feedback loop each time i boost the fx loop signal.
All i want to know is how to get rid of this crosstalk. Better Shielded cables ? moving the FX Loop circuit ? converting the Loop to serial ? and how is it done on my amp.
If anybody knows a way i would be grateful to hear it (read it).

[Jazz P Bass]

These TSL amps are a snake nest!
I do not see that any modifying is going to be easy.
If at all possible.
I do seem to recall that the TSL 100 had both serial & parallel loops.
That is why I reprinted the manual.
They new it was a compromised loop.
So forget the boost pedal. That is for parallel.
As to the delay, can't you turn off the delay box?

[maejima]

So there is no way to mod the loop for serial rather than parallel operation?
My goal is to use the footswitch to engage the loop for an instant solo sound with more volume, a little bit of delay and chorus (maybe an EQ to boost the highs a bit). If i can't do that , then the loop is of no use to me.
I've read post here that explain mods done to TSL for more stable Bias and better switching and a lot of other stuff that seem too complicated. I think that converting the Loop to a serial one should be possible.

[Darkhorse]

I have a Carvin V3 head which has both a series and a parallel loop. You might reference their specs (call them and ask about the issue) to see if you can figure out how they run them.

Obviously your amp has a parallel loop which combines the signal 50/50 from the loop. I have never had a use for my parallel loop, effects wise, although they recommend some delays or reverbs on full effect mix can work as the signal will be mixed with the straight signal.

I put a patch cable on mine and with the lopp level all the way up it gives me a nice clean boost effect. (The amp has a front panel clean boost so this mod gives me 2 which are foot switched and channel memory capable, really cool amp, all tube circuit).

I have done a lot of reading on some loop issues and you can out some booster pedals in the loop, many do. The problem is a booster in front will not give you and vol increase just a gain increase no doubt you noticed this. So to get a vol boost for leads or dynamics they put the booster in the loop.
Most amps these days have gotten away from having loops set to only line level. Many are set to instrument (pedal) level or have level or pad controls to match. Obviously if you get a vol drop when having a box in the loop it is line level. Some boxes, mainly delays have a seclect option to raise the output to line level (+3db).
I personally have to have any delay or chorus in the loop. Try running in the loop your Chorus into Delay and then your booster, this will give you the options of a vol boost w or without the delay or chorus on. This is not what most do typically but it is workable subject to individual effects. One reason why there are few set rules because all pedals act differently. I have even run entire chains and my guitar synth right into the effect return bypassing the amps preamp entirely. You having a parallel loop complicates issues. If you have mix controls on your chorus and delay try panning all the way to wet no dry and see what that does.

[pdf64]

Re-arranging the TSL fx loop to a footswitchable series type would not be simple /trivial, but rather would take quite a few hours of an EE's time in order to develop a solution.
Maybe Jerry at FJA Mods could help you out? Pete.

[maejima]

Thanks for all the replies. I figure there's no much hope for the loop problem , although when i tried a Digitech Digidelay in the loop i did n't have the signal drop and there was more settings for me to go to that could withstand the feedback loop problem. Maybe i will get a delay like that for mild use in the loop and that's that. I don't think i can send the amp all the way to America to FJA mods to make the loop work. That's why i tried to find a DIY solution but it seems that there is nobody else with that same problem on a TSL60. Anyway many thanks guys.