Marshall MG100HCFX Preset Fix: Stop Random Changes
The Client’s Challenge
A client, a gigging guitarist, reported an intermittent but recurring issue with a Marshall MG100HCFX amplifier head during live performances. The presets would appear to change spontaneously, indicated by the preset number display beginning to flash or ‘swirl’. This behaviour occurred without any manual adjustment of the amplifier’s controls, causing unpredictable changes to the guitar tone mid-performance.
System & Environment
- Hardware: Marshall MG100HCFX Guitar Amplifier Head
- Environment: Live stage environment with high Sound Pressure Levels (SPL)
- Symptom: Stored presets become unstable, indicated by a flashing parameter light, without user input.
Diagnosis
The diagnostic logic centred on the function of the flashing parameter light. In most digital or digitally-controlled analog equipment, a flashing light on a preset indicates that the current physical state of one or more controls does not match the stored values for that preset.
Root Cause Analysis
The root cause was identified not as an electronic fault, but as a mechanical sensitivity inherent to the amplifier’s design. The physical potentiometers (knobs) for parameters like Gain, Volume, and EQ are sensitive enough that sustained acoustic vibration from the speaker cabinet in a live setting can cause them to physically move by a minuscule amount. This ‘parameter drift’ is sufficient for the amplifier’s firmware to detect a mismatch between the knob’s new physical position and the saved preset value, triggering the flashing indicator and potentially altering the sound. This is a known behavioural characteristic of this amplifier series.
The Fix
The solution is a procedural workaround that mitigates the hardware’s sensitivity to vibration. By zeroing the physical controls after storing a preset, the potential for vibration-induced parameter drift is eliminated. The stored digital values are recalled correctly, independent of the physical knob positions.
-
1
Create & Store Preset
Dial in your desired tone using the amplifier’s physical knobs (Gain, Bass, Mid, Treble, etc.). Once satisfied, save this configuration to a preset channel according to the manufacturer’s manual.
-
2
Zero All Parameters
Immediately after the preset is confirmed as stored, physically turn all parameter knobs to their ‘0’ (zero) or fully counter-clockwise position. This includes channel volume and master volume if applicable.
-
3
Recall Preset
When you need to use the sound, recall the preset using the digital channel selector or footswitch. The amplifier will activate the stored digital values, not the physical knob positions. The sound will be correct and stable, as the zeroed knobs cannot drift.
Additional Reflections
Hardware Design vs. Fault
This case is a notable example of a hardware characteristic that behaves like a fault under specific conditions. The issue is not a component failure but a consequence of design choices regarding potentiometer sensitivity. While frustrating for the user, it is technically ‘as designed’. This highlights the importance of understanding the physical limitations and behaviours of equipment, especially in high-vibration environments like live stages. The workaround, while procedural, is effective and provides the required stability for professional use.
If you are seeking professional help with unstable presets on a Marshall MG100HCFX amplifier due to parameter drift from stage vibration, one-on-one remote support services are available from Audio Support.