Muddy sounding effects device in serial FX loop
If the AMP1's FX loop is set to serial, the mud is probably due to the fact that the effects device cannot handle the input level of the FX loop. This can happen with devices that are primarily designed for use in front of the amp (e.g. Nux Time Core, BOSS DD2 or general vintage pre-effects). For this case, the AMP1 has the FX level switch in the recess on the underside of the device. If this is set to -10dB, the problem is usually resolved.
Attention: If the FX loop of the AMP1 is set to parallel , there may be other reasons for poor sound results from effects devices in the FX loop: Thin sounding effects device in parallel FX loop