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Old 3rd August 2012, 12:52 PM   #1
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Default ganged output transformers

I was thinking of a way to get cheaper output transformers for a project.
Since their job is to impedance match the speaker, what happens if we transform the impedance twice or even three times but putting transformers in series?
for example. a 12v transformer is a ratio of 10:1. so three of them in series would be 1000:1.
if we applied that to an 8ohm speaker it would give a plate resistance of 8000ohms.
Is there a flaw in my theory?
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Old 3rd August 2012, 01:24 PM   #2
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Hi!

Impedance is transformerd by the winding ration squared. So a 10:1 transformer gives a 100:1 impedance ratio. Power transformers are not necessarily useful for audio signals. Soe might work when used properly. But most will not. better get a suitable transformer for the job.

Thomas
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Old 3rd August 2012, 01:32 PM   #3
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Originally Posted by Vinylsavor View Post
Hi!

better get a suitable transformer for the job.

Thomas
of coarse I know this....I'm just pondering ideas over morning coffee sitting on the deck.

so to continue the thought...in theory, we could put two line transformers in series to give the proper impedance match of a speaker.
What two 120v transformers would match an 8ohm load?
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Old 3rd August 2012, 02:23 PM   #4
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Hi!

Putting two transformers in series would most likely give very unpredictable results. You should select a matching near the value that is required for the output stage.

Decent output transformers are not expensive. Or salvage some transformer from an old radio. That would give muc better results than arbitrarily ganging two power transformers together

Thomas
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Old 3rd August 2012, 02:31 PM   #5
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Yes yes i know, use the proper part for the job. I am.
I'm merely thinking out loud on a theory.
by the calculations a 120v primary and a 5-6v secondary would match a 8ohm load with roughly 3300-4600ohm impedance, with only one transformer. (obviously a power transformer is not designed properly for audio applications. again I know this.)
So two transformers in series to give 5-6v out would do the trick, technically speaking...
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Old 3rd August 2012, 02:56 PM   #6
Fenris is offline Fenris  United States
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Most (all?) power transformers aren't air gapped, so single ended is out. You would need a dual primary 240v (120-120v) transformer for push-pull. I prefer toroids since in general they have a wider usable bandwidth compared to EI transformers. I've used a single primary toroid in a parafeed arrangement:

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Old 3rd August 2012, 03:02 PM   #7
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I never understood air gapped. transformers are a mysterious beast.
so put primaries in series and secondary's in parallel and use push pull output.
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Old 3rd August 2012, 03:08 PM   #8
DF96 is offline DF96  England
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Sorry to be blunt, but if you don't understand transformers what facts do you have to base your thinking on?

Things you need to learn about include: magnetic saturation and air gaps, magnetic hysteresis, impedance transformation, primary inductance and LF response, leakage inductance and HF response, stray capacitance and HF resonances. Once you can begin to understand these issues then you can begin to think meaningfully about transformers.
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Old 3rd August 2012, 03:19 PM   #9
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Be blunt, I'm an ignorant hacker just wanting to learn.
My thinking is solely based on pure ratios.
I know this idea isn't viable, or it would have been done 1000 times before.
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Old 3rd August 2012, 03:37 PM   #10
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I never understood air gapped. transformers are a mysterious beast.
so put primaries in series and secondary's in parallel and use push pull output.
Your goal is to understand this plot: File:Permeability by Zureks.svg - Wikipedia, the free encyclopedia

Try to read and understand this:
Magnetic field - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Permeab...ctromagnetism)

You think you can achieve that ? It is not that hard when you get the deal with fluxes and flux densities.
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