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Old 16th May 2005, 07:15 AM   #1
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Default will laziness burn my amp down?!

I'm used to building battery powered guitar pedals, and I've dicided to build a tube amp.
specifically, thefirefly tube amp .
where i live i have 220vac from the wall outlet, and the amp itself needs 207vac, and it seems a little silly to me to add a transformer: 220 to 207...
can i just connect the amp to the power grid with no transformer?
is there another way to "get rid" of 13 volts? a risistor perhaps?
will it burn if i dont get rid of 13 volts?

all help is apriciated.
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Old 16th May 2005, 07:18 AM   #2
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For safety sake all equipment should contain a mains transformer even if it is only 1:1. It could very well save your life or the life of someone near and dear to you one day.
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Old 16th May 2005, 08:32 AM   #3
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Unless you are on a mission to become a 'rock and roll suicide' you will definitely need a transformer. Transformerless ht was often used in old valve radios but this meant that every part of the circuit including the chassis had to be insulated and not 'touchable' by a user. The reason: If the mains polarity gets reversed, the chassis becomes live - in your case, your guitar would become live
You will need a transformer to supply the heaters anyway so why not find one which does both
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Old 16th May 2005, 09:28 AM   #4
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Quote:
Originally posted by AudioFreak
It could very well save your life or the life of someone near and dear to you one day.
Thanks, that was important ...and you definatly spooked the [not so nice word] out of me...
to the 2nd question: if i add a 1:1 transformer, will i still be endangering me or my closest?
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Old 16th May 2005, 10:31 AM   #5
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I have an idea. What if I connect one wire to mains live and orher to ground? Also, i use only one diode to rectify AC, so chassis is grounded.
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Old 16th May 2005, 11:01 AM   #6
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Guys,

How much is your life worth to you and your family/friends?

More than the 30-40$ it would cost for a mains transformer?
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Old 16th May 2005, 12:07 PM   #7
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Old 16th May 2005, 12:50 PM   #8
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Quote:
Originally posted by pinkmouse
Guys,

How much is your life worth to you and your family/friends?

More than the 30-40$ it would cost for a mains transformer?
I would use the transformer if I were able to get it. Using two transformers (one to lower the voltage second to raise it again) is OK for small power, but for higher power it costs and weights too much.

Could anyone explain why my idea is wrong? Chassis is grounded, so noone would get hurt if touch the chassis. If I touch chassis and B+ at the same time I would get almost the same shock even if I would use a transformer.
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Old 16th May 2005, 01:02 PM   #9
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If your amp were plugged into a socket, or had a cable with live and neutral/earth reversed, the whole thing would be at mains, including any instruments plugged into it.

Once again, is your life really worth less than 30-40$? Really?
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Old 16th May 2005, 01:36 PM   #10
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"Could anyone explain why my idea is wrong? Chassis is grounded, so noone would get hurt if touch the chassis. If I touch chassis and B+ at the same time I would get almost the same shock even if I would use a transformer."

Your idea is wrong because it's deadly.
A transformer will give you isolation and, most importantly, will limit the amount of current that will surge through your body when you touch the B+ line. Without a transformer, the current is limited only by the rating of your circuit breaker (or fuse).
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