I’ve been trying to locate the cause of blocking distortion on a friend’s Line 6 Flextone 3 XL combo. Characteristics of the problem are: on low signal levels, the sound decays and gets “chopped off”, similar but not as neatly as a noise gate would work, whilst high signal levels (for example, hard strumming on the guitar) would sound fine.
On the Line 6 Flextone 3, the input jack socket is mounted on the chassis and has a preamp circuit on a PCB. Firstly, the jack socket itself should be checked for good conduction – if it appears excessively tarnished or oxidised, it’s worth replacing it.
Secondly, the input socket PCB assembly is connected to the main board via a cable with Molex style push connectors. A bad connection in the connector can cause the blocking distortion problem.
Clean both connector parts, with something like an interdental toothbrush and some metal polish – not forgetting to clear out the residue with either rubbing alcohol or contact cleaner – and then secure the connector either with hot melt glue or silicone. This has worked for me, resulting in a crystal clear input signal once more.
Of Sound Mind 