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Reducing the voltage on an unregulated PSU
Reducing the voltage on an unregulated PSU
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Old 7th December 2018, 02:28 AM   #11
rayma is offline rayma  United States
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Quote:
Originally Posted by nigelwright7557 View Post
Yes me too, the mains can sometimes fluctuate a bit.
Certainly, and allow +/- 10% additional for that.

Any kind of capacitor derating helps with reliability and lifetime,
including temperature, voltage, ripple current.

Last edited by rayma; 7th December 2018 at 02:30 AM.
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Old 7th December 2018, 03:48 AM   #12
hirscwi is offline hirscwi  United States
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Reducing the voltage on an unregulated PSU
Quote:
Originally Posted by nigelwright7557 View Post
As I use unregulated supplies I usually limit my TDA7294 to +/- 35 VDC.
That makes sense to me. I hay have a transformer that will work.
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Old 7th December 2018, 10:49 AM   #13
Kay Pirinha is offline Kay Pirinha  Germany
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In my opinion, the best solution would be #3. As new transformers usually aren't that cheap, the 2nd best solution form #3 comes into mind. I'd modify it, though: Arrange the supplementary transformer as a real autoformer, i.e. connect the 120V primary in series with the 12V secondary, observing the right phase. Then connect the amplifier's tranny to the 120V and mains power to the ends (132V).
The supplementary xformer's wattage may be much smaller than the amp's maximum power consumption - only one tenth of it in this case.
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Last edited by Kay Pirinha; 7th December 2018 at 10:51 AM.
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Old 8th December 2018, 01:44 AM   #14
MAAC0 is offline MAAC0  Portugal
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Look at the middle column TYP. With 40V you are at max spec, any line fluctuations can lead to over-voltage. I would go for 35V max for 8 Ohm and 27V for 4Ohm.
As 40V/8Ohm=5A & 5A*40V=200W. Can the chip handle it at long term ?
Perhaps with forced cooling and more than 10% distortion.
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Old 8th December 2018, 04:03 AM   #15
hirscwi is offline hirscwi  United States
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Reducing the voltage on an unregulated PSU
Quote:
Originally Posted by MAAC0 View Post
Look at the middle column TYP. With 40V you are at max spec, any line fluctuations can lead to over-voltage. I would go for 35V max for 8 Ohm and 27V for 4Ohm.
As 40V/8Ohm=5A & 5A*40V=200W. Can the chip handle it at long term ?
Perhaps with forced cooling and more than 10% distortion.
Thank you for the explanation.
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Old 8th December 2018, 04:09 AM   #16
hirscwi is offline hirscwi  United States
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Reducing the voltage on an unregulated PSU
Quote:
Originally Posted by MAAC0 View Post
Look at the middle column TYP. With 40V you are at max spec, any line fluctuations can lead to over-voltage. I would go for 35V max for 8 Ohm and 27V for 4Ohm.
As 40V/8Ohm=5A & 5A*40V=200W. Can the chip handle it at long term ?
Perhaps with forced cooling and more than 10% distortion.
Thank you for the explanation.
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Old 8th December 2018, 04:35 AM   #17
asuslover is offline asuslover  Romania
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Reducing the voltage on an unregulated PSU
+/-40v would be maximum for that chip, your psu is not usable for your amp, dropping 10VOLTS x 3-5Amps(assuming a stereo amp) would be to much heat dissipated in that amp case. Just buy a 22-25 volts dual secondaries 200va transformer.
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