The sunn Forum
Sunn Musical Equipment => Q & A => Topic started by: Ben Dead on January 05, 2010, 01:23:06 pm
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Can someone explain to me the purpose of the 'Polarity' switch on the older Sunns? I have an early 70's Studio P.A.
Thanks.
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i could be wrong and i'll eat a bug-but i think the polarity switch was put on there when there were ground problems before the three prong plug came along. outlets in homes and well, anywhere were only two slots for two prongs-sometimes that brought buzz-supposedly the polarity switch would eliminate that buzz.
they dont do anything these days.
http://stanosaur.com/
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Most of the places that we played in the late 60's and 70's had 2 prong electrical outlets on the stage, if they had any power at all. To avoid a bad ground "hum", you flip the switch to reverse the polarity and it reduced the "hum". That is also why a lot of the heads you see from that era have power supply cords with cut off ground prongs (mine too).
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Thanks. Have a good one.
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It should also be noted that the polarity switch is exceptionally dangerous despite having a purpose in the original design. Look at how AC works if you're unfamiliar. This system is way before I was born but I have no idea how AC was even considered safe without a ground.
Anyway, what you need to do is take the polarity switch out of the circuit all together. The reason you can do this is because all modern outlets have 3 prongs (hot, cold, ground). You hook ground to the chassis and the other two don't matter...because they're contantly changing.
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i actually plan on taking it out. i have the amp taken apart right now because it stopped working. i found a resistor that was burnt to a crisp. i'm no electrician or amp tech, so it's going to be a big project getting this thing working again. i tried to post pictures on one of my other posts, but it was asking me to import the pics from a website. so, once i have time to do this i'll have pics up.
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Good luck. Just remember to be careful and ask questions if you have them. These things look complicated at first but they're dead simple. You just have to get comfortable with electronics. But you're in good hands because this is exactly how I started years ago.