Ok... it seems a speaker is a reactive load as well as a resistive load....

So I have to use trig to calculate this? Is this correct?

 

Hmm...

Kchriste, shouldn't the calucluation be done with 50V peak and not 100V peak...
The amp is being supplied with +/- 50 volts dc....
It's output is gnd & signal ... which is good as it allows me to ground the transducer...
Since the peak voltage is half of the peak to peak?

So... RMS voltage would be 35.35Vrms and then curent would be 1.17A rms..
which makes the RMS power 41.4 watts...

Am I right, wrong or totally confused?

 

Allrighty...

If my corection above is right... And I want to calculate what voltage I should be driving the transducer at, for maximum power of 200 watts.... then....

Using V = SQRT(P * R) = SQRT(200 * 30.33) = 77.9 V RMS
Which is 110.1 Volts peak .... So I should be running +/- 110 Volts into the transducer...

Is this correct?

 

Yes, you'd need apx 110Vpk (77.9 RMS) into a 30hm: load to get 200 watts.

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woot!!

I finally got something right! maybe I'm learning someting....

Thanks!

 

Allrighty...

I put the scope on the transducer ... and its actually seeing about 40v pk...

Each amp is supposed to be able to handle 100 watts...

I could invert the input to one of the amps and then bridge them... but then I would lose my ground.... this would give me 80v pk...
Since the trnasducer body is one of the conenctions... I really don't want to sacrifice my ground...

So... wouild it be possible to use a transformer with one side grounded and run the amps in parallel? Here is a schematic...

The transformer ratio would be 2.75... Would a common/standard transformer work at 28kHz??

Thanks,
Michael

Attached Images

xfmr conctns.jpg (41.0 KB, 3 views)

 

Hey~~

Seems like I would need a autotransformer with a powered iron core for high frequency...

Perhaps it would be more efficient to toss the amps and just switch the rectifed mains voltage ... We get 220ac here in South Korea..
But since I already have the amps I think I wil lgo looking for an autotransformer with a powdered iron core...

Could someone confirm that this would be a possible solution??

Thanks,
Michael

 

No, a mains transformer would not work.
Use a powered iron core transformer with isolated windings. Drive the primary with the bridged amplifiers and the isolated secondary can connect to the transducer and ground. You'll probably have to wind your own transformer. This is assuming that the amplifiers can put out 200W in bridged mode.

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Allright....

So I should invert the signal to one of the amps and tie their grounds together.... and drive the primary of the transformer with the signal form amp 1 and the inverted signal form amp 2...

Here is a pic...

Thanks,
Michael

Attached Images

xfmr copy.jpg (45.4 KB, 2 views)

 

Yup, that should work.

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Hi agian....

Since I'm having a hard time finding a suitable transformer....

I think I will start from scratch and build an amp that will deliver the 77 VRMS without using a transformer on the output...

For comparitive purposes... A 1.5 kW amp driving a 4ohm load would output 77 VRMS I need...

Into a 30 ohm load... there would a considerable surplus of current ...
So I should be able to hack away some of the output transistors...

I should prolly start a new thread for this since its a bit off topic of the original...

Thanks for everyone who helped...
Michael

 

Just Make a transformer. Its not that difficult and definately cheaper than what your proposing below.

A Ferrite "E/I" core would be best considering the frequency involved. And it should be a Power ferrite Material, such as made by "Fair Rite" and there material "77".

Total transformer cost probably under $5.00

And Why would you need a 1.5 Kw Amp to drive this?
Piezos are usually more of a Voltage operated device, rather than high current or power.

Good Luck....Gary

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Hi~

The comment I make about the 1.5kw amp ...was, as I said, for comparative purposes...

As, it would require the same voltage (77 VRMS) to drive 1.5kw into a 4 ohm load...
As 200 watts would be into a 30 ohm load... (77 VRMS)

On the line under that, I mentioned "there would a considerable surplus of current ..."
And I could remove some of the output transistors as to remove the current surplus...

As for using a transformer... thanks for the tip about making one...
However.... I have been advised that the kit amps I already have (based on 2sc5200 and 2sa1943) will prolly not handle 200 watts at 28 khz...

So I might as well start from the beginning.... and just build an amp that doesnt need an output trasformer...

Which is what Im currently doing... found a schematic online for an amp that will take +/- 125 VDC... (not the 117 from esp)...
Monday I will prolly pick up the parts for it...

Thanks,
Michael