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Class D Switching Power Amplifiers and Power D/A conversion

The best Class D amp for 30w 4,6 Ohm speakers
The best Class D amp for 30w 4,6 Ohm speakers
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Old 13th September 2017, 09:34 AM   #11
Khron is offline Khron  Finland
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How much power do you need / want to get out of it?

No matter what chip you go with, you're limited by your power supply, and virtually all of them will distort at the same level if you power them with only 12v.

Can't get away from good ol' Ohm's law (the one i used earlier, P = U^2 / R; P is power, U is the RMS voltage across the load, so 0.7 times the supply voltage; R is the nominal impedance of the load or speaker).

To get even close to the advertised power specs, you'd need to power them with close to their maximum nominal supply voltage (24-26v or so).
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Old 13th September 2017, 10:28 AM   #12
SGr33n is offline SGr33n
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I'd like to power the loudspeakers at their maximum power, how much can I squeeze them? so I will also try powering the 7492 with 24v (8v-24v). It also have 2 dip switches for 21.6dB, 27dB, 31.1dB, 33.6dB. The distortion is less on 21.6dB, setting it at 33.6dB looses bass power and produces more distortion. Increasing the voltage will also make it possible to set 33.6dB?

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Old 13th September 2017, 10:35 AM   #13
Khron is offline Khron  Finland
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Do you NEED that much gain from the amp itself? Or rather, what's the signal source for it?
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Old 13th September 2017, 11:22 AM   #14
JMFahey is offline JMFahey  Argentina
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As famous Audio veteran Enzo says: "the amplifier is that thingie between the Power Supply and the Speaker" meaning: you can only get so much peak voltage at the speaker terminals as you have available at the power supply (minus a couple Volts losses) which of course determines available power, headroom, etc.

No matter what amp you connect between that supply and speaker, even if 100% efficient, you won´t get more out than you put in.

So in a nutshell: if current amp is not enough, build a larger one, with the corresponding higher voltage (and current) power supply.

Any other amp you hook up to the original one won´t change much, if t all.

From what you say, a 30 to 60W per channel amp will be fine to improve headroom and usable level.
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Old 13th September 2017, 12:14 PM   #15
SGr33n is offline SGr33n
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Quote:
Originally Posted by Khron View Post
Do you NEED that much gain from the amp itself? Or rather, what's the signal source for it?
I don't know if I really understood your question, the signal is bluetooth audio. Those speakers came from an old, broken Bose SoundDock, so I replaced the electronics with the 7492 and it didn't sound loud and clear as the original. So do I have to leave dBs to the lowest value? The quoted by Enzo is an interesting and real point of view.
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Old 13th September 2017, 01:46 PM   #16
Khron is offline Khron  Finland
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It has been often observed that the higher the gain on these class-D chip-amps, the more noise you get on the output, so it's generally agreed you'll want to set that to the lowest selectable value.
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Old 13th September 2017, 04:05 PM   #17
SGr33n is offline SGr33n
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Perfect! I will update this thread as soon as I will do these changes. Thank you all!
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Old 14th September 2017, 03:14 AM   #18
Peterm100 is offline Peterm100  Chile
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I'm using a 15V Mean Well power supply which works well. I was using a 12V wall wart at first and heard distortion on peaks, but after beefing up the power supply and adding the big cap i haven't been able to produce any distortion. I believe this is simply because the new power supply provides more available current and isn't depleted like it was with the wall wart. I also noticed a distinct improvement in transient impact and dynamics with the new power supply and cap.

Another note, I'm using this on a small fairly high efficiency desktop system, biamped and actively crossed over at about 300Hz so the amps aren't very stressed.
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Old 15th September 2017, 10:36 AM   #19
ICG is offline ICG  Germany
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Aside from the voltage, the wall warts usually don't have enough power.

If you want more power and the (low voltage) power supply can deliver it, you could still go for a buck converter (dc/dc converter). They aren't expensive anymore and a real solution, or, if you want to look at it from another side, it gives you a much better, greater choice of amplifiers.
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Old 15th September 2017, 10:45 AM   #20
Khron is offline Khron  Finland
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A pretty usual (and often dirt cheap) way to power these smaller class-D amps is old laptop power bricks.

I'd rather go for used brand-name ones, than new crap chinese ones, but they're 19v and anything between 3A and 6-8A, so plenty of juice available.

Stick with HP / IBM / Lenovo / Dell ones, and if you can see the label, Delta / LiteOn / HiPro / AcBel are the usual (and pretty good quality) suspects
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