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Old 4th November 2014, 02:29 PM   #1
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Default Designing an audio transformer for an underwater acoustic power amplifier for the pur

Hi friends,
I am new on the forum and hope to learn a lot here. I want to design an audio transformer for an underwater acoustic power amplifier for the purpose of Impedance matching. I want to know how to calculate turns, impedance, watts, etc. Unfortunately there are few literature surveys on this issue. I have glanced at Wolpert’s audio transformer design manual. But there are still some vague points, e.g. I have not found an equivalent circuit for the audio transformer to know exactly know what elements it is made up of and how they are joined to each other. I have also found a software named OPT Design Assistant. I have a lot of doubts about the correct way to use it. Even if I knew how to use it, I would not be able to design the audio transformer. Because, as mentioned before, I have not found an equivalent circuit for the audio transformer. Now I am seeking your help; any info about the problem will be very useful to me. Any help is also appreciated.
Thanks a lot, farshid.
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Old 4th November 2014, 06:18 PM   #2
TheGimp is offline TheGimp  United States
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Location: Johnson City, TN
RDH4, Radiotron Designer's Handbook volume 4 is available on the web and chapter 5 extensively covers transformers.

Search RDH4 PDF.
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Old 4th November 2014, 07:09 PM   #3
dmills is offline dmills  United Kingdom
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Note that most underwater transducers are piezo ceramics and appear as a fairly high Q series tuned circuit with a largeish capacitor across it (Sort of like the classic model of a crystal, no surprise).

That fixed capacitance when reflected through the impedance ratio of the transform can appear as a HUGE capacitive load on the amplifier which can cause stability issues.

The classic answer is to make the secondary of the transformer resonate with the transducers fixed capacitance, and use some series resistance to kill the Q at transducer resonance (Usually in a 5th order network or so).
The objective is usually to end up with a couple of more or less equal sized peaks in the admittance curve so that in total you get a reasonably flat response over maybe a decade (About as good as it gets in sonar TX transducers).

This is more of a matching problem then a transformer problem (And the voltages can get totally scary), spice is your friend.

Regards, Dan (Who used to do that **** for a living).
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