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Old 20th February 2004, 09:00 PM   #1
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Default 400W in a chip

... supposedly, according to the simulation. But I haven't been able to get even 1W out of it I'm trying to use a TDA7454.

May be it's because I screwed up when I was first powering it up: Forgot to connect Power Ground (some noise came out of the speakers).

Or may be it's because y connected only two speakers (one gets both Right outputs (rear and front), the other one gets both Left outputs). Can that be done?

I'm using a computer PSU to get +12VDC, which should be enough. I'm getting Vcc out of the Left speaker terminals and +3V out of the Right speaker terminals.

Now I rewired everything just the way the datasheet says, and nothing comes out. Is it too late now?

Please help!!!
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Old 22nd February 2004, 06:24 PM   #2
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In short - no, it can't be done. Either connect 4 speakers, or use the front connection only.

Every output is a bridge pair. Have you parallelled the rear and front amps for left and right, respectively? If so, you're effectively shorting them, because the front and rear amps are connected at low power levels, but in opposite phase, in order to reduce dissipation at low levels. Just follow the app note, OK?

Edit: How do you arrive at the figure 400W? I can't get it to more than 4x60W at 14.4V @ 2ohms.
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Old 23rd February 2004, 12:30 AM   #3
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Default Thanx, and another question.

Thank you very much for replying.

I got the 400W figure by running the simulation at http://www.st.com/stonline/products/...in/audpowl.htm and by clicking on TDA7454.

I used 17V for the supply, 2 Ohm impedance, full distortion (I'm intending to use this as a guitar amp), my heatsink is rated at 0.65, ambient temp is 40șC. Using music as the sample gives me a peak power of 4X99.5W.

Just one more question: Can I connect both Front outputs to one speaker, and both Rear outputs to another speaker?

Meanwhile ... back to the drawing board.

Yours,
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Old 23rd February 2004, 05:20 AM   #4
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No, as I read it, you have to keep the outputs apart. It seems like it might be possible to connect a speaker between front and rear outputs since the rear amp is inverting, but that would still behave like a standard bridge, so it makes more sense to just connect the speakers as drawn in the appnote.

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Old 23rd February 2004, 05:25 AM   #5
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Default Thanks, again

Thank you!

I'll try that.
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