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Old 12th February 2013, 10:33 PM   #1
Sh00pus is offline Sh00pus  United States
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Default TDA7265 Over 18V at 4 ohms

I decided to build an amplifier with the TDA7265 with a 12.6-0-12.6V transformer which will give me roughly +/- 17.8V. But i know that transformer are not made perfectly and there will be some range, so my question is, what if my transformer ends up outputting more than 18V on each side. I looked the the output power vs. supply voltage for 4 ohm load and I see it ends beyond 18V. Will something bad happen or will it just have a higher output wattage?
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Old 13th February 2013, 03:00 PM   #2
johnr66 is offline johnr66  United States
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I think you are safe. The ~18v you measure should be for no load or very light idle load. The supply voltage will fold back under load. What is the transformer's current rating?
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Old 13th February 2013, 06:34 PM   #3
Sh00pus is offline Sh00pus  United States
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The transformer I'm using can supply 2.5A. I hope that's enough to run it.
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Old 13th February 2013, 07:10 PM   #4
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by Sh00pus View Post
what if my transformer ends up outputting more than 18V on each side. I looked the the output power vs. supply voltage for 4 ohm load and I see it ends beyond 18V. Will something bad happen or will it just have a higher output wattage?
Higher output power comes with bigger volume. The rated (max) output power brings very high distortion. You don't want to hear that. You may be disturbed cranking the volume, so expect only volume opening to give less than 10W.

But if you're crazy enough trying to hear the loudest sound, then before reaching max output power, the chip total dissipation will climb much faster and may break the chip. The lower the load (worst case is output short) the faster this to happen. So, monitor the chip temperature to find out the likely maximum volume for a known speaker.
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Old 13th February 2013, 07:53 PM   #5
johnr66 is offline johnr66  United States
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With a 12.6-0-12.6 2.5a 63va transformer, you will get around 11 - 12 watts per channel with 8 ohms or 15 - 16w @ 4 ohms. This is continuous sine wave, both channels driven, no clipping. No problem at all as you are running the IC with a low supply voltage.

I'd rather run them a bit low rather than push them with near the limit supply voltages. If I need more power, I move on to a higher power IC.
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Old 13th February 2013, 10:24 PM   #6
Sh00pus is offline Sh00pus  United States
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Thanks, I think I will look for a more powerful chip. since i'm running 4 ohm speakers i'm really near the limit.
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Old 14th February 2013, 03:11 AM   #7
Jay is offline Jay  Indonesia
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BTW, what is your maximum power expectation (some of us are happy with 3W). I'm trying various chip amps to find the best one. My current amp (have been 2 days) is a TA... eww I forget. It is rated for 6W/8R/1%. But with carefully selected good parts, it is very good and you will agree that THD number is not as bad as it looks.

I will temporarily finalise it today and move to TDA2030V (previously I tried TDA2030A), or may be TDA7265, I'm not sure.
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Old 14th February 2013, 03:15 AM   #8
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My current best chip amp family is also relatively low power - TDA856xQ. I started out with TDA8561 and TDA8566 sounds just as good, maybe even better. I've given up with the usual fare - TDA7265 sounds OK on bass/mid duty but way too dull at the top. I haven't tried these chips into 4R, into my 8R speakers they're good for about 13W.
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Old 14th February 2013, 03:42 AM   #9
Jay is offline Jay  Indonesia
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Originally Posted by abraxalito View Post
TDA7265 sounds OK on bass/mid duty but way too dull at the top.
If I'm not mistaken, that was the reason I didn't go with TDA7265 for my "extreme" project.

TA82XX is a better candidate. But I want to try TDA2030V first because I know how good it is.

New lessons learned from the latest/current project:
1) Sanyo Oscon is not good in signal path compared to regular BP/NP. But it is good as FB cap, as long as it is given a few hours to break in
2) Holco resistor is not good only in series FB resistor, but also in shunt FB resistor. "Better" than the gray Caddock resistor.
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Old 14th February 2013, 03:47 AM   #10
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Isn't TDA2030V just a particular form of lead bend on what's the same die as TDA2030A? Or am I missing something? Seems to me that amps with LTP in the input stage are always hamstrung by that. Degeneration helps though - many of the LM3xxx have resistors in the LTP.
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