Υπάρχει μια περίπτωση, όπως λέει το παρακάτω link, να συμβαίνει (αν κατάλαβα καλά) όταν έχεις unbuffered fx loop...
"We’ll keep this one simple. Most modern amps come with a buffered effects loop to help compensate for the lower level output of most stompboxes. In a non-buffered effects loop this lower output can cause a somewhat anemic tone. A buffered effects loop makes up for this signal mismatch and cures the problem. If you’re suffering from the woes of a non-buffered effects loop, there are products that are designed to help such as the Ceriatone Klein-Ulator. Most mainstream amplifiers will have a buffered effects loop while boutique amplifier builders may only offer this as an additional option."
Link http://proguitarshop.com/andyscorner/fx-loops-explained