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Old 20th November 2004, 10:29 AM   #1
icebear is offline icebear  Norway
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Default Placing the powertransformer

I have a question regarding how to place the trannys on the amp to minimize the hum. Look at the picture. Is this the rigth way to do it, or should I turn the the powertranny 90 deg. ?


Bjørn
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Old 20th November 2004, 11:20 AM   #2
mcs is offline mcs  Denmark
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It looks fine to me.

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Mikkel C. Simonsen
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Old 20th November 2004, 11:21 AM   #3
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The laminations of the power transformer should be at right angles to the laminations of the OPTs. If the power transformer is the one on the left, it is correct. Don't forget, if you use a filter choke, it may be a good idea to mount it at right angles to both the power transformer and the OPTs.

EDIT: looks like mcs beat me to it 25 seconds....
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Old 20th November 2004, 11:34 AM   #4
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Is this where I add one of them annoying "Me three" posts?

Another option, if your filter choke is a small one (like the Hammond 158-series) instead of the X-mounts, is you can put it underneathe the chassis at a right angle to the power and due to the top/bottom offset to the OPT's, there will be minimal pickup....especially if you use a non-magnetic chassis, like aluminum, copper or *real* brass.
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Old 20th November 2004, 12:34 PM   #5
icebear is offline icebear  Norway
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It's a Decware SE84SC. There is no choke.

Bjørn :-)
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Old 20th November 2004, 12:56 PM   #6
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It looks OK.
But you can do an experiment!
Connect a loudspeaker at the OPT outputs and connect at the primary of the power transformer the 110 or 220V.
Place the power transformer or the OPTs at different positions to see what happens with hum.It's a nice experiment!
You don't need to connect anything else!You can do the experiment without the transformers on the chassis.Do it very carefully on your bench.

Be carefull not to touch anything on the secondary of the power tranny
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Old 20th November 2004, 01:16 PM   #7
GeirW is offline GeirW  Norway
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Gday.

Am not sure there is a downside to this approach,
but why not shield them with copper cans.
It deffinetly will not harm the look either.
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Old 20th November 2004, 01:40 PM   #8
mcs is offline mcs  Denmark
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Copper doesn't shield magnetically, as far as I remember. Power transformers are also generally not designed for encapsulation - it will get too hot.

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Old 20th November 2004, 01:50 PM   #9
GeirW is offline GeirW  Norway
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Gday.

F.ex: K.E moded marantz products uses copper to shield trans.
but with seperation walls.
Quote:
Power transformers are also generally not designed for encapsulation - it will get too hot.
I was thinking along those lines, so a separation plate
would maybe be the thing.
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Old 20th November 2004, 01:56 PM   #10
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Some manufacturers use a thin copper layer around the transformer to shield them.It's not a can!A lot guitar amps have this kind of shielding on the transformers.
But even with this you can have hum with wrong positioning!The tranny doesn't look nice,too.
With my experiment you can kick hum at 100%.
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