I need to ramble on a bit. A long time ago, oooh….about mid-’70’s, I was working in the service department of Hudsons Music in Chesterfield. There were three of us; Dave, Danny and me. And the very excellent guitar teacher, Fred Baker, used to wander through the workshop from time to time.
You might think that luck has nothing to do with electronics, but you would be badly misguided in that opinion. Of the three of us, Dave had the most ridiculous degree of good luck. He could fall into a barrowful of horse shit and jump out smelling of Chanel. Danny would fall in and come out smelling of horse shit, and I would fall in and never get out again.
What, you might wonder, has this got to do with anything? Well, it eventually might (with a bit of luck) get to a Marshall preamp/ recording/ headphone drive/ pedal. But to resume. On this occasion, Dave had checked through an early ’60’s Selmer Treble and Bass amp head, and it had gravitated to my bench with the advice that,
“It just wants a couple of preamp valves”. Dave had switched it on earlier, and apart from not making any noise at all, had sat on his bench, quietly, for the best part of an hour.
I took the back off, and the amp, performing to an audience of three (Dave Danny and Fred) blew the main reservior capacitor to bits, decorating my jumper with its insides, and filling the room with smoke. This was thought to be a hilariously funny Christmas tree impression. My point is that, had I been the one to donate the amp to Dave’s bench, it would have behaved with perfectly good manners.
Onwards and upwards, to the Marshall preamp pedal. Belonging to Paul, he freely admitted plugging in a dc supply of the wrong polarity. Inside most pedals, there is a diode which protects the internal chips. The idea is that if you apply the wrong polarity supply, the forward-biased diode shorts the dc input and blows the fuse in the power supply. Unless you are unlucky. In which case, the diode blows open, the protection doesn’t protect and the internal electronics are fried.
In other words your nice pedal is converted to a pile of junk. Why they don’t use a series diode to protect the protection diode I don’t know.
Suffice it to say that my decorated jumper was well worth the three cups of tea and a macaroon.