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Old 22nd February 2008, 10:37 AM   #1
cs is offline cs  United Kingdom
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Default TDA7294 clipping

This is really a follow-up to my earlier post on LM3886 clipping.

Datasheet wise, the TDA7294 looks roughly comparable to the LM3886 (but can be bought very cheaply), so I wondered if anyone has done any measurements regarding clipping behaviour ? Googling didn't come up with anything.
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Old 22nd February 2008, 10:53 AM   #2
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You mean a scope shot of a clipped sine wave ? What frequency 1 or 10 Khz , what load ----- 8 or 4 ohms ? Have you some prior knowledge if this is a problematic area ?
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Old 22nd February 2008, 11:00 AM   #3
cs is offline cs  United Kingdom
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Quote:
Originally posted by ashok
You mean a scope shot of a clipped sine wave ? What frequency 1 or 10 Khz , what load ----- 8 or 4 ohms ? Have you some prior knowledge if this is a problematic area ?
Yes, a scope shot would be ideal.

I guess 10kHz and 4 ohms would be best to highlight any adverse behaviour. I'm not aware of any specific problem, but I would just like to find out before starting on my project. The amps (either LM3886 or TDA7294) will be used in some active speakers.
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Old 22nd February 2008, 02:47 PM   #4
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OK. I was going to do this anyway , I'll just hurry it up.
You are lucky . I have both LM3886 and TDA7294 boards .. still populated with parts !
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Old 22nd February 2008, 05:41 PM   #5
cs is offline cs  United Kingdom
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Quote:
Originally posted by ashok
OK. I was going to do this anyway , I'll just hurry it up.
You are lucky . I have both LM3886 and TDA7294 boards .. still populated with parts !
Great, thanks Ashok.
Look forward to seeing your results.

Chris.
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Old 23rd February 2008, 05:00 PM   #6
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Quote:
Originally posted by ashok
OK. I was going to do this anyway , I'll just hurry it up.
You are lucky . I have both LM3886 and TDA7294 boards .. still populated with parts !
I wonder what happens if you arrange (adjust voltage) a test where the output powers match (nearly) between the two amplifiers? Otherwise the test couldn't be a head-to-head comparison, while the application for one differs from the other.

If that's not possible, please include LM3875 in the testing as a reference point for triangulation.

So, let's see what the measurements show.

I'm so curious. But, since the application differs, then I'm not sure how to apply the measurements. How to?
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Old 23rd February 2008, 05:19 PM   #7
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I can only test the TDA2050/7294 and LM3886/1875

Don't know what you are expecting but all boards are working ( at the moment!) and psu's are rigged up and so I can do it without much effort. A couple of weeks down the line the situation might change ( usually does !).
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Old 23rd February 2008, 09:20 PM   #8
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Maybe try a comparison when TDA7294 is operating on a slightly higher voltage than LM3886?

I just think its very interesting to "rig" both amps for same output power, same gain (as in signal + power = output), and then compare them.

Another comparison point, application wise, is their performance per same thermal disappation. Actually, that's almost the same comparison point that I'm talking about anyway--just a different way to see it.

Its no secret that the less powerful TDA7294 is going to wipe the floor with LM3886, IF used on the same power supply. This means nothing whatsoever, because of, signal + less power = cleaner, lesser, output. That's not an even comparison. If you try this, notice how much cooler is the TDA7294, and how much less output there is. So, there's no baseline reference for comparison, and, these useless figures are already documented. Instead. . .

What is a secret. . . What happens with a truly even head-to-head comparison between the two?

I'm so curious.
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Old 24th February 2008, 05:48 AM   #9
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Quote:
Originally posted by danielwritesbac
Its no secret that the less powerful TDA7294 is going to wipe the floor with LM3886, IF used on the same power supply. This means nothing whatsoever, because of, signal + less power = cleaner, lesser, output. That's not an even comparison. If you try this, notice how much cooler is the TDA7294, and how much less output there is. So, there's no baseline reference for comparison, and, these useless figures are already documented. Instead. . .
No, that's not even remotely true. Look at the six graphs on page 12 of the LM3886 datasheet. The lowest THD+N for steady state signals is acheived at the point just before clipping. I don't know if this is the case with TDA7294, but considering it's true of nearly all SS amps, it probably is.

What this means is that less output has more THD+N. For LM3886 at 1kHz into 4ohms with 28V rails, THD+N is about 0.03% at 20mW output and 0.004% at 20W.
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Old 24th February 2008, 05:53 AM   #10
soongsc is offline soongsc  Taiwan
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I do recall the LM3886 can take higher voltages, and thus probably will clip at a higher voltage. The LM3886 runs quite cool driving an 8 ohm load whereas the TDA7294 runs warmer just sitting there. I tried palying both, but using different power supplies. Liked the LM3886 better.
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