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Old 10th April 2017, 12:11 PM   #1
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Question Suggestion for 12V stereo amp circuit with 30W+ RMS for 4 Ohm speakers

Hi everyone!
I'm new to DIY audio and only have basic electronics knowledge, but I know how to solder things together.
I would like to build an amplifier for a portable music system powered by a 12V lead battery. I already found a lot of circuits, keywords like "Gaincard" and "Symasym" and chips like LM3886 and TDA2030. But I don't really know which fits my needs:
  • Power supply: 12V DC (lead battery)
  • Stereo sound / 2 channels
  • A volume control (preferably only one for both channels)
  • For speakers with impedance of 4 Ohm
  • At least 30W RMS, preferably more
  • Input source would be the "amplifier output" of a car radio or simply a phone/MP3-player/...
Sound quality does not have to be extraordinary good as I won't be using high quality speakers. Volume/power is more important, as I plan outdoor usage. But then, if I can build something decent for the amplifier, I might change the speakers later.


Can anyone point me in the right direction?
Thanks!
Ray
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Old 10th April 2017, 04:19 PM   #2
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9 Vrms is 11.8 v peak. You'll never get 9 out of 12 v rail with class AB, more like 6. (6^2)/4=9 W That's V^2/R=P
Needs an inverter, a boost switcher supply, or more rail voltage.
class D is not for amateurs.
Buy a car amp or Class D amp maybe. One rated for 4 ohm speakers.
Or go to Power supplies and learn to make switcher boost supplies. I can't do it yet & I've got 58 years experience in the electronics hobby.
I'm dinking with making a blown CFL, less the shorted lamp tube, turn 12 vdc into 24 vdc. Cost of parts so far, zero.
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Old 10th April 2017, 04:37 PM   #3
rayma is offline rayma  United States
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Quote:
Originally Posted by xlray View Post
Power supply: 12V DC (lead battery)
You can double the output voltage swing, and quadruple the output power, by using a bridged amplifier circuit.
A Guide for Building TDA2003 Bridged and Stereo Amplifiers - Circuit Basics
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Old 11th April 2017, 04:55 AM   #4
PRR is offline PRR  United States
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12V DC is "car battery". Which implies car-sound amplifiers.

The basic is rayma's "bridge". These give 16W-22W into 4 Ohms.

The next step is Jo's DC-DC up-converter. Not an easy DIY proposition; you can buy it cheaper than you can build it. Go to the loud-car shop, they got from 2X45W up to 2X750W, different prices, size, and time-to-flat-battery.
Kicker 43DXA125.2 - 30 watts RMS x 2
JL Audio XD800/8v2 -75 watts RMS x 8
Kicker 44KXA2400.1 - 2,400 watts RMS x 1
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Old 12th April 2017, 09:19 AM   #5
AndrewT is offline AndrewT  Scotland
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the most one can get from a 12V single supply is ~4Vac.
If you bridge a pair of those amplifier you can get upto 8Vac from TWO amplifiers.

Bridging requires each amplifier to be capable of driving a load of half the impedance of the actual load attached to the bridged outputs.
If you want to use a 4ohms speaker to get maximum output power, then each amplifier has to be rated to drive a 2ohms reactive speaker load.

Thus to get 8Vac from a 12Vdc single supply you need TWO amplifiers rated at 8W into 2ohms and that will get you to 16W into 4ohms as your final output. (note this is double the 2ohms rated output power, NOT quadrupled).
But you will struggle to get that from a 12Vdc supply. Increasing the supply to 13Vdc, or maybe 13.5Vdc, may get to the 16W into 4ohms target.

Now lets look at the amplifier spec:
each amp has to meet an 8W into 2ohms and that requires 4Vac (=5.66Vpk) and 2Aac (=2.83Apk) into a 2r0 dummy load. A real speaker is more likely to demand at least 150% of that and a reactive 2way more like 300% of that, i.e. 8.5Apk.
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Last edited by AndrewT; 12th April 2017 at 09:23 AM.
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Old 12th April 2017, 09:44 AM   #6
JMFahey is offline JMFahey  Argentina
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Short answer: you can get good 16W RMS using 12V and car type bridged amps, from 2x TDA2003 to 1 x TDA2005 (same thing) to modern Class D amps.
The limiting factor is having meager 12V to work with.
Didn´t check Rayma´s link but that should be it.
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Old 12th April 2017, 04:52 PM   #7
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there was class H, but i bet you won't really find any class H chips .

TDA1562Q pdf, TDA1562Q description, TDA1562Q datasheets, TDA1562Q view ::: ALLDATASHEET :::

45-55 watt at 0,5 % THD from 14.4 volt supply into 4 ohm.
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Old 12th April 2017, 05:25 PM   #8
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take a look at the tpa3116 tpa3118 stereo and mono boards on ebay the mono boards parallel the stereo outputs so you can drive 2 ohm loads.


the chips can be used up to a maximum of 26 volt power supply. Later you can get a booster from 12 to 24 volt and get 50 watts into 4 ohm with the stereo board and 100 watts into 2ohm with the mono board.
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Old 17th April 2017, 06:15 AM   #9
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Quote:
Originally Posted by Arty View Post
there was class H, but i bet you won't really find any class H chips .

TDA1562Q pdf, TDA1562Q description, TDA1562Q datasheets, TDA1562Q view ::: ALLDATASHEET :::

45-55 watt at 0,5 % THD from 14.4 volt supply into 4 ohm.
Class H is a trademark of Hitachi, for a line of amplifiers using Class G topology. As such it isn't a "real" amplifier class, as recognized by the AES or IEEE, but a marketing tool. It is similar to Class T (trademark of Tripath's Class D topology) or Duo-Beta (trademark of Luxman's Class AB topology). They are attempts to imply an exclusive technology when actually employing a recognized one.
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Last edited by Johnny2Bad; 17th April 2017 at 06:22 AM.
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Old 17th April 2017, 12:39 PM   #10
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well sure its just a marketing thingy.
but anyways what it does that it has its own "methood" to boos supply voltage so you can get a load of OOOOMPHS from a low voltage single supply. witch was the request of the OP.
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