Hi guys (and hopefully girls)

I tried to build an ultimate pedal board but ran into a problem when it was completed

I run delay & tremolo in effect loop (amp effect loop) and I wanted to add my RC300 loop station after all.

Because effects loop goes after pre-amp I would expect signal to be strong and amplified however it's absolutely weak. I put instrument volume to max (on RC 300) and still never haver a clip no matter what I do. The signal (volume) is still very low - which doesn't make any sense to me.

If I do it in series - everything's ok.

My Amp - Fender Twin (1996)

Not sure what to do about it at all I can't put loop station in series because I'll loose my delay & tremolo and I can't put delay before pre-amp because I do hear the difference

Any suggestions/ideas ?

Thank you.
Is it a parallel loop? Does it have an FX level switch? Can you get a completely wet signal if the loop is parallel? It may be that the FX send is strong and expects a strong signal back but the RC300 cannot output that high. You need to set the FX loop to ~-10dbm if it has a level switch.
Thanks Fly, keep forgetting about effects loop volume switch.

dry/wet is called mix on twin and it was set to 10 (out of 10) so that was ok.

I do have it with -13 -6.5 and +2 options. It was set to -6.5 when I changed it to +2 I finally got the right volume. So "problem" solved. Thank you.

However it's unclear to me why you say that it should be set to -10. Is it common practice ? am I missing something?
The reason I say that is because loopers are designed to go after the guitar and pedals, which are generally in the -10dbm range. My Jamman looper is overdriven in the loop of some amps that are line level. I looked at the specs for the RC300 and it says the output is nominal -10dbm.

However, nothing is carved in stone and it's a mystery to me what +2 works better. But sometimes things aren't what they seem and you found the solution.