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Bargain amplifer S350HS TPA3251, If i use it on a car. Do i need a 12v step up 30v dc to dc ? or will the board support the 12v from the car.
- Thread starter wric01
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staticV3
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Car battery voltage is usually well above 12V while the alternator is running, so the board should power up just fine.
Output power will be limited though.
Roland68
Master Contributor
I would advise against something like that. In a car, you'll have fluctuating voltages, voltage spikes, and interference. A device like that isn't designed for that. It's also not designed for vibrations and shocks.
You can get enough amplifiers in that price range, like a Pyle with 4 x 100 watts. That makes much more sense.
- Thread Starter
- #4
Got a plug in hybrid, and got a led cigarette monitor is constantly 12.4-14 v never dip. Should be stable enough. it's 45$ . Only reason i drool about this : is because it's a TI
TPA3251 purepath tech aka that same rave reviewed Fosi v3 higher watt brother tpa3255. I like the option of the subwoofer amp within which why i don't really care about 4 ch amp.
DVDdoug
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High power car stereos have internal voltage-boosting power supplies.
12V peak-to-peak is 4.2V RMS and that's 2.2W into 8-Ohms or 4.4W into 4 Ohms.
With a bridge amplifier you can get 24V peak-to-peak for 4 times the power.
...Power is inversely proportional to impedance and proportional to the square of the voltage.
...This is the reason you sometimes see 2-Ohm or even 1-Ohm woofers for cars. The amp doesn't have to boost the voltage as much if they can make it put-out the current required for the lower impedance load.
12V peak-to-peak is 4.2V RMS and that's 2.2W into 8-Ohms or 4.4W into 4 Ohms.
With a bridge amplifier you can get 24V peak-to-peak for 4 times the power.
...Power is inversely proportional to impedance and proportional to the square of the voltage.
...This is the reason you sometimes see 2-Ohm or even 1-Ohm woofers for cars. The amp doesn't have to boost the voltage as much if they can make it put-out the current required for the lower impedance load.
The bold print in your post says it works from 12V.
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- Thread Starter
- #6
Maximum Supply Voltage 30v, reason i asked is because i want the amp to reach it's potential 220W as i am unsure what the car 12v amperage it'll push as it's powering 2 ch and a sub ch vs a step up to30 v might increase it's chances of more watt.
Roland68
Master Contributor
The 220 watts is a fantasy figure from the chip manufacturer's datasheets.
Really well-designed TPA325x amplifiers with good components have achieved 62 watts of maximum power into 4 ohms at 32 volts in tests, for example, the Fosi V3 stereo. That's the actual measured power.
I just saw that the amplifier has two TPA3251, one in stereo BTL mode and one in mono PBTL mode. This would allow 2 x 50 + 1 x 60 watts at 30 volts under optimal conditions, but probably still illusory.
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I'm not sure you have the expertise for this project based on your questions. There will be ground loop noise, guaranteed in a car environment and difficult to fix. 30 volts will give you max power. You won't get it from 12 volts. You will need fairly thick power cables from the battery to the amp to get any decent power out of it. Many people overlook this and end up with hot cables and limited power. Also you need to optimize the load for what the amp is capable of for max output - 2 ohms? 4 ohms?
I once helped a friend hook up a 100x100 watt amp in his car. Initially he used wiring that was already present in the trunk. He complained that it wasn't very loud - I measured the power at the speakers and it was pushing about 5 watts per channel. I had him run some really thick power cables back there, maybe 4-6 gauge, can't recall, and then it pushed the full 100 watts a side into 4 ohms.
I once helped a friend hook up a 100x100 watt amp in his car. Initially he used wiring that was already present in the trunk. He complained that it wasn't very loud - I measured the power at the speakers and it was pushing about 5 watts per channel. I had him run some really thick power cables back there, maybe 4-6 gauge, can't recall, and then it pushed the full 100 watts a side into 4 ohms.
DVDdoug
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Here are some formulas -
Power = Voltage squared / Impedance. (For audio, which is AC, this is RMS voltage.)
The theoretical maximum peak-to-peak voltage you can get out of a regular amplifier stage is the same as the DC supply voltage. Or a with bridge amplifier which puts-out two opposite-phase voltages (two "hot" outputs with no ground to the speaker) you can get double. That's the theoretical maximum. There is some voltage-loss in through the amplifier and the current may be limited and that creates more voltage loss.
For a sine wave the peak-to-peak is 2.8 times RMS. If you are in the U.S., the wall voltage is 120 RMS = 339V peak-to peak, or 170V peak (rounded numbers).
Or, the RMS voltage is .353 times the peak-to-peak.
I believe the TPA3251 is normally used in a bridge configuration so the theoretical maximum RMS output voltage would be 0.707 x the power supply voltage.
The datasheet says:
3 Description
...The device can drive up to 2 x 175 W into 4-Ω load and 2 x 220 W into 3-Ω load...
If you read the details that's at 36V with 10% distortion.
It's not unusual for amplifier manufacturers to fudge their specs.
I tend to trust the chip manufacturer more but they are testing/specifying under best-case conditions and it may not end-up as good in the final product.
Power = Voltage squared / Impedance. (For audio, which is AC, this is RMS voltage.)
The theoretical maximum peak-to-peak voltage you can get out of a regular amplifier stage is the same as the DC supply voltage. Or a with bridge amplifier which puts-out two opposite-phase voltages (two "hot" outputs with no ground to the speaker) you can get double. That's the theoretical maximum. There is some voltage-loss in through the amplifier and the current may be limited and that creates more voltage loss.
For a sine wave the peak-to-peak is 2.8 times RMS. If you are in the U.S., the wall voltage is 120 RMS = 339V peak-to peak, or 170V peak (rounded numbers).
Or, the RMS voltage is .353 times the peak-to-peak.
I believe the TPA3251 is normally used in a bridge configuration so the theoretical maximum RMS output voltage would be 0.707 x the power supply voltage.
The datasheet says:
3 Description
...The device can drive up to 2 x 175 W into 4-Ω load and 2 x 220 W into 3-Ω load...
If you read the details that's at 36V with 10% distortion.
It's not unusual for amplifier manufacturers to fudge their specs.
I tend to trust the chip manufacturer more but they are testing/specifying under best-case conditions and it may not end-up as good in the final product.