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Author Topic: 70v and conventional speaker system voltages...  (Read 9138 times)

ryancousins

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70v and conventional speaker system voltages...
« Reply #10 on: April 21, 2014, 02:13:17 pm »

That helps clear things up. I just assumed the step up transformer after the amp and the step down transformer before the speaker were the same ratio, just in reverse.

When I learned about transformers in my electrical theory class, I was taught that the coupling between the two coils is nearly 100% efficient, regardless of the turns ratio, so I never thought about a transformer presenting or changing an impedance.


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John Roberts {JR}

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Re: 70v and conventional speaker system voltages...
« Reply #11 on: April 21, 2014, 02:19:11 pm »

That helps clear things up. I just assumed the step up transformer after the amp and the step down transformer before the speaker were the same ratio, just in reverse.

When I learned about transformers in my electrical theory class, I was taught that the coupling between the two coils is nearly 100% efficient, regardless of the turns ratio, so I never thought about a transformer presenting or changing an impedance.


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In fact the impedance transform is the transformer turns ratio squared. So if the voltage is altered by a factor of 2x the impedance shifts 2^2 or 4x. While there are resistive losses in windings, yes generally power transfer is 1x. So the impedance transform can be derived from Ohms law. As the voltage goes up the current must fall for the power to still equal unity.   

JR
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Steve M Smith

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Re: 70v and conventional speaker system voltages...
« Reply #12 on: April 21, 2014, 02:24:37 pm »

The turns ratio of a transformer is equal to the square root of the source impedance divided by the load impedance,

So a transformer to match an 8 ohm speaker to a 500 ohm amplifier output stage would be the square root of 500/8 or about 7.9:1

Transformers are most useful in valve (tube) amplifiers to convert their high voltage, low current (high impedance) output stage to a low voltage, high current (low impedance) to drive a speaker.


Steve.
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Richard Turner

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Re: 70v and conventional speaker system voltages...
« Reply #13 on: April 22, 2014, 12:03:10 pm »

old thread here , some of the links still work

http://forums.prosoundweb.com/index.php?topic=566.0

home page article here

http://www.prosoundweb.com/article/understanding/

Some amplifiers output at 70v or there abouts when loaded with transfortmer speakers, yorkville AP4040 is somewhere about 75v QSC pl340 was about 85 volt, theres an equation somewhere to do the math.

The key is to use good quality transormers or fidelity will suffer, that isnt really an issue if its just a paging system, human voice only but for a background music system it will.
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Re: 70v and conventional speaker system voltages...
« Reply #13 on: April 22, 2014, 12:03:10 pm »


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