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Old 9th March 2009, 09:47 PM   #1
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Default Bridged LM4766 resistor wattages

Hello

Are there any resistors in this circuit that need to be more than 1/2 W?
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Old 10th March 2009, 12:49 AM   #2
CJ900RR is offline CJ900RR  Sweden
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Yes the Rsn-resistors (zobel network) should at least be 2W. But my opinion is that you dont need zobel in most cases, so you can leave them and the cap's behind out of the circut if you dont have them...
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Old 10th March 2009, 11:07 AM   #3
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Sorry, I actually posted the wrong circuit.

I meant to post a Bridged LM4780:
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Old 10th March 2009, 12:41 PM   #4
Dxvideo is offline Dxvideo  Turkey
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I like LM4780s sound without the snubbers (Rsn+Csn) too. But you must try both with snubber and not.. If you decide to use them then they should be 2W or more..
Once, I fried a couple of 1W resistors in that position..
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Old 10th March 2009, 07:44 PM   #5
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Quote:
Originally posted by CJ900RR
Yes the Rsn-resistors (zobel network) should at least be 2W. But my opinion is that you dont need zobel in most cases, so you can leave them and the cap's behind out of the circut if you dont have them...
Max supply voltage is 32 V, which leads to a maximum output voltage of ~19V AC.
According to the datasheet 1/4 W is enough. Rule of thumb is to use resistors with 100 % safety margin, so we can only load it with 1/8 W. 4,7 Ohm needs 0,5875 V for that. The impedance of the 100 nF capacitor would have to be lower than 147,3 Ohm to achieve that voltage drop across Rsn. That is the case above ~10800 Hz. Is the supply voltage 32 V? And if so, what could lead to continuous nominal output at 10800 Hz or above?

Quote:
Originally posted by Dxvideo
I like LM4780s sound without the snubbers (Rsn+Csn) too. But you must try both with snubber and not.. If you decide to use them then they should be 2W or more..
Once, I fried a couple of 1W resistors in that position..
With 2,7 Ohm it takes 1,64 V to reach 1 W. With max supply voltage of 38 V you get ~24 V AC out. The impedance of the 100 nF capacitor needs to fall below 36,8 Ohm for 1,64 V across the resistor. That is the case above ~43200 Hz. Sound like serious oscillation.

Rsn should be 1/4 W as per datasheet. If it burns, find out why and fix the fault.
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Old 11th March 2009, 04:20 AM   #6
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Sorry to keep jumping around here..I was reading false information about the supply voltage requirements.

Totally sure about this one, and the supply will be 12V. I know it's kind of ridiculous, but it's just an experiment with a car battery.
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Old 11th March 2009, 08:11 AM   #7
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Quote:
Originally posted by ballsingtripp
Totally sure about this one, and the supply will be 12V. I know it's kind of ridiculous, but it's just an experiment with a car battery.
The TDA7294 works from supply voltages betwen 10 V and 40 V. It will not work from 12 V.
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Old 11th March 2009, 08:18 AM   #8
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Quote:
Originally posted by pacificblue

The TDA7294 works from supply voltages betwen 10 V and 40 V. It will not work from 12 V.
Am I missing something?
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Old 11th March 2009, 08:22 AM   #9
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10 V = 20 V.
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Old 11th March 2009, 08:29 AM   #10
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Oh..seems strange. Does that have something to do with the battery or is that just how they're usually referred to?

Could you recommend any amps that would work?
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