Can I parallel transformers for a LM3886? - diyAudio
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Old 25th October 2003, 02:49 AM   #1
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Default Can I parallel transformers for a LM3886?

I have an LM3886 amplifier driving a 4-ohm subwoofer speaker, and think that high distortion at low volume levels is caused by my low power transformer. I know it puts out 25-0-25, at I think a little below 1 amp. Can I connect two of the same transformers in parralel, anotherwords connect the three outputs of each together to double the power into the rectifier?

Or would this not be a cause of the distortion?

Thanks, Mike
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Old 25th October 2003, 10:54 PM   #2
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the problem with this is that it is akin to putting 2 voltage sourece in parallel, only with a small resistance in between. If you can determine the difference in actual output voltages, you can begin to analyze the feasibility of this endevor. either the resistance between transformers must be increased, or a resitor must be added in series with 1 primary (to lower voltage at the econdary. make sure phase isn't affect though!

i would just get a larger transformer though.
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Old 26th October 2003, 06:47 AM   #3
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The very best thing you can do is to use two recifier bridges. Then you totally safe but if the transformers are identical it's usually no so bad connect the windings directly in parallel. You should bebeware of potential risk of having currents flowing from the one transformer to the other. The only side effect you will get is warmer transformers.
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Old 26th October 2003, 11:49 AM   #4
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I heard a funny story once about someone bringing a small power plant online in Idaho. It seems that he connected the leads together while his station was still 30 degrees out of phase with the rest of the world.

20 miles down the road, a transformer the size of my house, picked itself up off the ground and rotated 30 degrees before setting itself back down.

Your phase has GOT to be exactly right.
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Old 26th October 2003, 12:18 PM   #5
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Could somebody tell me exactly what phase is? I know that you can invert phase using opamps, but this sounds different. And, how do I make sure that the phase is the same on both transformers?

And, does the "warmer transformers" mean hot, or warm, and can it mess them up?

Thanks, Mike
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Old 26th October 2003, 01:12 PM   #6
paulb is offline paulb  Canada
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Phase is like polarity for AC. Pretend there's a + and a -. If you connected two batteries in parallel, but had + to - and - to +, that would be bad. It's the same with transformers.
If the transformers are identical, you should be able to find and connect the exact same wires together. As an experiment, maybe put a 1K resistor or something between each connection the first time you hook them up - there should be very little voltage across each resistor.
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Old 26th October 2003, 01:18 PM   #7
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Quote:
Originally posted by Nappylady
I heard a funny story once about someone bringing a small power plant online in Idaho. It seems that he connected the leads together while his station was still 30 degrees out of phase with the rest of the world.

20 miles down the road, a transformer the size of my house, picked itself up off the ground and rotated 30 degrees before setting itself back down.

Your phase has GOT to be exactly right.
Happened at one of big hydropower plants in the north of
Sweden once. They accidentally connected it out of phase.
The shaft between the generator and the turbine got
very twisted. I suppose it ruined the whole turbine, at least.
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Old 26th October 2003, 01:47 PM   #8
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I suggest that SOUNDnerd starts with my suggestions and forget about nuclear power plants for a moment.
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Old 28th October 2003, 01:19 AM   #9
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Yes, peranders is right. I am just building a simple power supply, not some power plant. I am not skilled enough to know how to use 2 rectifiers, and since the wires connect into the transformer inside and they come out a hole in the bottom, there is a 50% chance of the phase not being right. I dont really like the idea of a subwoofer picking itself off of the ground and doing somersaults across the room.

I think that I will just take the easy and expensive way out by buying a larger transformer.
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Old 28th October 2003, 02:51 AM   #10
MWP is offline MWP  Australia
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I directly paralleled two 500VA torid transoformers in an amp i built.... works no problems.
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