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I just got off the phone with James and Tom at Booker Labs. They heard about my post through the grapevine and have offered to look the switch over while they’re modding my LBB.?

To satisfy your curiosity, though, it’s just an spdt footswitch and a TRS jack in a tiny enclosure. The tip and ring are connected to the outer lugs of the switch and the ground is connected to the center lug. Thinking about it, what should really surprise me is that it doesn’t always shock you, since it’s sending 12V to ground either way. I’m clearly missing something.?

Thanks for offering to help, regardless!?

Andrew

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Well, to start with, 12 volts isn't enough to give you a shock. You could for example grab one terminal of a car battery with each hand and not feel a thing, even with wet hands. Secondly, you're not switching a high current 12 volt source to ground, you're connecting 12 volts through a resistor to ground. When the switch is open, this 12 volts is used to switch the internal logic of the LBB to one state, when the switch closes the 12 volt input to the logic becomes 0 volts and the logic changes state and operates the internal switching? to change the Leslie speed.

If you're sometimes getting a small shock from the switch this suggests that some AC mains current is getting to the chassis ground of the Leslie or the LBB. This shouldn't be able to happen if everything is properly grounded to a three pin power outlet. If there was anything more than the slightest leakage, the safety breaker on current house wiring systems would trip and cut the power off. If you're using a two pin power oulet, it's not uncommon for mains transformers in vintage equipment (such as a 122 Leslie) to have enough leakage (strictly speaking the charging current of inter winding capacitance rather than an actual connection) to cause sufficient AC voltage to appear on the chassis of the Leslie, and thus the chassis of any connected equipment, to cause a "tingling" sensation when the chassis is touched.? If the two pin mains plug isn't polarised, you may well find that you get a tingle with the plug in one way round but not the other.

I just got off the phone with James and Tom at Booker Labs. They heard about my post through the grapevine and have offered to look the switch over while they’re modding my LBB.?

To satisfy your curiosity, though, it’s just an spdt footswitch and a TRS jack in a tiny enclosure. The tip and ring are connected to the outer lugs of the switch and the ground is connected to the center lug. Thinking about it, what should really surprise me is that it doesn’t always shock you, since it’s sending 12V to ground either way. I’m clearly missing something.?

Thanks for offering to help, regardless!?

Andrew

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After my last post, I googled the LBB and looked at it on their website. As you say it does have a two pole mains connector. As the Leslie is powered through the LBB, it effectively also has a two pole connector. I would say that the small shock you are getting is almost certainly coming from the Leslie, due to the charging current of the interwinding capacitance, rather than any breakdown of insulation. The best work around, without going to the trouble of providing a mains ground to the Leslie chassis, is to find which way round the mains input plugs are fitted when you don't get a shock, both the inlet to the LBB, and the wall plug. Then mark the plugs so that you always fit them this way around. Maybe Booker Labs will be happy to fit a three prong, grounded mains inlet for you when they do the other mods. The only possible downside of grounding old equipment with this problem is that enough current may flow to ground to trip modern safety breakers. You may remember the recent discussion about replacing the mains wiring on a B-3. Some people said they always update to three prong grounded mains connectors when rewiring, others said no because of problems with safety circuit breakers tripping. There's no easy answer to this, one of the joys of using vintage electrical equipment! I well remember 40+ years ago when clubs started fitting saftey circuit breakers to their stage power supply to protect artistes, even brand new Hammonds and Leslies in perfect working order could sometimes cause these circuit breakers to trip out.

It's certainly not much of a shock. A little more so than licking a 9V battery.

I'm glad, going by your explanation, that I'm having the pros look it over. The LBB does, in fact, have a two-prong outlet. Next time it happens, I'll have to test the Leslie itself with my multimeter.

Many thanks!

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