Use AC speakers in Car

[Nauman Muhammad]

That is what small cheap speakers do. No bass, probably no highs and not much loudness.
If your car battery is fully charged at 13.8V then the rectifiers will reduce it and feed about 12VDC to the circuit. But the 11.9VAC has a peak voltage of 1.414 times higher than 11.9V at 16.8V and the rectifiers reduce it to 15V which is 25% more than the 12V.

Powered from only 12VDC the very cheap and small amplifier IC probably produces a max output of 8VAC which produces only 2W into the tiny 4 ohm speaker. Ordinary car radios produce 14W in each speaker.

I agree that the Kenwood disk changer will blow up the cheap tiny speakers.

Thank you, will step up work? i.e if I use 12v to 19v dc step for car?

 

[Audioguru]

The little speakers were designed to be powered from 11.9VAC which produces 15VDC. Why do you want to maybe blow them up with 19V?

 

[FuZZ1L0G1C]

Regarding rectified AC.. above thread...
Would the AC, which if 11.9V pk-pk, not be +5.85V - 0V - -5.85V?
Then, after smoothing pos half-cycles & ripple, no-load V is +5.85V?
Then with load, depending on transformer power and load, about 5>4.5V DC ?
Or even at 18V p-p this still rectifies to 9V...
Or am I missing something?

 

[Audioguru]

Regarding rectified AC.. above thread...
Would the AC, which if 11.9V pk-pk, not be +5.85V - 0V - -5.85V?

No because the transformer produces 11.9V RMS (peaks of 16.8V) , not 11.9V p-p. Also the transformer has only 2 wires without a center-tap.

Then, after smoothing pos half-cycles & ripple, no-load V is +5.85V?

No because your half-wave rectifier produces a 0.9V voltage drop down to +4.95V. The actual 16.8V is reduced to 15V.

Then with load, depending on transformer power and load, about 5>4.5V DC?
Or even at 18V p-p this still rectifies to 9V...
Or am I missing something?

You are talking about using a different transformer that is 4.2V RMS center-tapped. Each half of the secondary produces peaks of 5.95V and a rectifier diode rectifies one half to make +5.04V and the other half is rectified with a second diode to make -5.04V. Then the total DC is 10.1V.

 

[FuZZ1L0G1C]

You are talking about using a different transformer that is 4.2V RMS center-tapped. Each half of the secondary produces peaks of 5.95V and a rectifier diode rectifies one half to make +5.04V and the other half is rectified with a second diode to make -5.04V. Then the total DC is 10.1V.

AHA! Thank you. Did basics in the mid 70's and had forgotten the theory.

 

[Audioguru]

I looked at your photos in your post #2 and see that the amplifier IC is an obsolete TDA2822M. Your volume control is a dual so the amplifier is stereo. The maximum allowed supply voltage is 9VDC when the speakers are 8 ohms (with a higher voltage the IC will overheat) and the power before severe clipping distortion is only 0.7W per channel with a 9V supply and is only 0.13W with a 4.5V supply. If the speakers are 4 ohms then the output power is about 1.8 times the above but the maximum allowed supply will be 6V.

 

[Ngauri]

how does the audio amplifier converts the DC supply to AC. I want to know this in detail for my project work. please help

 

[kellys_eye]

Amplifiers that use a split rail supply (i.e. +ve, 0V, -ve) simply replicate an AC signal which is, after all, a signal that swings +ve and -ve about a zero point.

Amplifiers that work on a single supply rail use a large capacitor to achieve the same effect.

 

[BobK]

Amplifiers that work on a single supply rail use a large capacitor to achieve the same effect.

I never thought about this before, but, the capacitor in the output of a single supply AC amp is basically the same thing as a switched capacitor negative voltage generator.

One end of it is tied to ground (through the speaker), while the other end alternates between V+ and ground with the audio waveform. When connected to V+, the capacitor charges through the speaker. When connected to ground, the other end now has a negative voltage and discharges through the speaker.

Bob

 

[Audioguru]

To produce 2W RMS into an 8 ohm speaker the voltage must be 4V RMS which is 11.3V peak-to-peak and the peak current must be 707mA. An amplifier with a single output can use a single 14.3V positive voltage and use power transistors to swing the output voltage up to +12.8V then swing it down to +1.5V then feed this 11.3V peak-to-peak voltage swing into an 8 ohm speaker through a coupling capacitor to block the DC.

Or two amplifiers can drive a speaker with one of them driving one of the speaker wires and the other amplifier driving the other speaker wire in a bridge. Then the amplifier is said to be "bridged". The voltage swing at the speaker is nearly doubled and the current in the speaker is also nearly doubled so the output power is about 3.5 times it was before at 2W x 3.5= 7W into 8 ohms or 14W into 4 ohms per channel (4 channels) like in car radios.

How? You need to learn about transistors to understand how.