This model has an envelope filter "Q-TRON" with an effect loop and a switch that adjusts the response to picking.
The inner part is arranged in the order of instrument → filter → effect loop, so the effect connected to the loop is used to add flavor to the sound after passing through the filter.
I bought it secondhand about 15 years ago and have kept it since then.
There is a sense of use overall. Please confirm with the picture.