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** No-one here is ever gonna get this - it is just too darn simple.On both occasions, when the input TL072 failed, the owner was neither at home nor a gig. He was using an upper floor room of a neighbour's very run down 120 year old terrace house for band rehearsal.
His amp made an unusual buzzing all the time, put down to dodgy power wiring.
The amp failed to proceed from the get go, after switching on & connecting his wall wart powered wha-wha pedal with a lead already plugged at the amp end. The amp was not earthed, so floating about 150VAC above ground due to stray C inside the AC tranny. So that sort of voltage was transferred momentarily to pin 3 of the TL072 via 10kohms as the plug tip touched the pedal.
About 20 mA peak - just enough to be fatal.
Other models of MusicMan amps I checked have protection diodes fitted or much greater input resistances. The sod of an owner was aware the room and it's ancient wiring had a lot to do with the failures, but kept it secret until I really pushed him.
On the grounds that it was worth a try to get free repair and mod.
Wot an utter ass. Never saw him or his MM amp again, the mod worked.
.... Phil