Power supply for sound system

[unclejed613]

that's assuming the outputs in those chips are EF.... they could very likely be CFP, in which case they swing to within 0.7V of each rail.

 

[deviator]

would car battery be enough?

 

[unclejed613]

from the looks of it, you would need two 12V batteries. a car battery isn't exactly portable.... maybe 2 small gel-cell packs..... if you want to see how it's done, look at the early Pignose portable guitar amps. they were the first to make portable guitar amps using chip amps and battery packs. i know you may not be using it for guitar, but the idea is similar.

 

[audioguru]

The original speaker system produced 30W into the sub-woofer. My calculation showed that an amplifier with a 32V supply will have an output of 30W into 3 ohms. how will you get 32V from a 24V battery?

 

[unclejed613]

he won't...

 

[vlad777]

Do you see the two yellow and a black wire in Photo0063.jpg .
Cut them on half or neerer to transformer
(the big metal cube thing). Take the transformer out (since you dont need it anymore).
You can use two 12V batteryes (which wont give full poWer)
or maybe use power(hand)tools battery packs which are 14.4V or more.
Connect plus of one bat to minus of the other and connect this to black wire.
Now you have free unconected two yellow wires and UNCONNECTED plus of
one bat and UNCONNECTED minus of the other. Connect yellow#1 to unconnected plus and the
yellow#2 to unconnected minus.If it dont work exchange #1 and #2
(yellow#1 to minus and yellow#2 to plus).

Your amp is linear which means it will waste energy.
Most battery hand tools have PWM (Pulse Width Modulation)
which makes bat last longer.

Edit:
But if the transformer has more than 5 wires coming out of it don't do this.

 

[bountyhunter]

The battery can supply 10.8V at 4.4A for one hour which is 48Whr, not 90Whr.
I have never seen an amplifier that has an output power as high as 30W with a supply voltage as low as 10.8V. A bridged car radio amplifier will have an output power of only 8.6W into a 4 ohm speaker at clipping when its supply voltage is only 10.8V.

That's true which is why car audio makers used to design systems running a pair of 3.2 Ohm speakers in parallel to get 1.6 Ohm effective impedance. We made power IC's that could source peak currents up to a about 6A to be able to drive signals into those loads.

 

[unclejed613]

Do you see the two yellow and a black wire in Photo0063.jpg .
Cut them on half or neerer to transformer
(the big metal cube thing). Take the transformer out (since you dont need it anymore).
You can use two 12V batteryes (which wont give full poWer)
or maybe use power(hand)tools battery packs which are 14.4V or more.
Connect plus of one bat to minus of the other and connect this to black wire.
Now you have free unconected two yellow wires and UNCONNECTED plus of
one bat and UNCONNECTED minus of the other. Connect yellow#1 to unconnected plus and the
yellow#2 to unconnected minus.If it dont work exchange #1 and #2
(yellow#1 to minus and yellow#2 to plus).

Your amp is linear which means it will waste energy.
Most battery hand tools have PWM (Pulse Width Modulation)
which makes bat last longer.

Edit:
But if the transformer has more than 5 wires coming out of it don't do this.

this will cause another loss of 1.4V, from the diode drops in the bridge rectifier. it's better to wire directly to the power supply caps (just make sure the polarity is right) and avoid the diode drops. power switch should be a DPST or DPDT (wired as a DPST) switch between the batteries and p/s caps.

these chips are most likely class AB, which will idle a few milliamps, don't worry about this kind of current draw or going to a PWM amp (and no there's no sense in "retrofitting" a pwm in this amp, nor is there a way to do it).

 

[deviator]

So there's this 3-pin 1 black wire (gnd) and 2 yellow ones (AC or something..) i connect gnd to (-) and AC's to (+) but the result i get there's totally no bass if i reconnect the wires to original (power transformer or something..) everything works fine... i tried switching the wires even trying to connect it with 3 wires, AC's to plus but result is the same either with one of them or both connected to plus. Some ideas would be nice.

 

[unclejed613]

what are you connecting to them? the amp for the subwoofer needs more current than the other amplifiers.. also you need two power supplies a +12V power supply and a - 12V power supply. if you're just hooling a single supply up it won't work right. if you hooked both yellow wires up to a single supply and the black to the - side of that supply, you only have a single supply rail active, and it won't work right.

 

[deviator]

holy ****, in other words i would have to buy for example 2x of let's say: LEMONA - AK-12V/3.3Ah Akumuliatorius 12V 3.3Ah Pb

 

[unclejed613]

so the voltages you need to supply to the amplifier are +/-16V. it will probably still work ok on +/-12V, but with less power. with +/-16V you get about 15W into 8 ohms, with +/-12V, you will get 9W into 8 ohms. that's a difference of about 2db.

yup i said that already.... +/- 12V means two 12V batteries...

 

[audioguru]

Modern amplifiers in car radios do not use two 12V batteries. Instead they use two amplifiers in a bridge so each end of the speaker is driven. The voltage to the speaker is almost doubled and the current is almost doubled so the power is almost 4 times as much as an ordinary single amplifier.
When the battery is being charged by the alternator at 13.8V then the power at clipping into 4 ohms is 15 Watts RMS. The peak power is 30W and this amplifier is rated at about 100 or 200 Whats per channel.

 

[unclejed613]

but we aren't talking about a car amp.... we're talking about a set of powered computer speakers that runs off +/-16V being run from a battery supply. i think the OP is trying to do this as simple and cheap as posible... it won't have as much power as it would running from +/-16V, but it will work and will be portable. if the OP wants to spring for separate lead/acid single cell gel-cell batteries, he could build +/-16V batteries using 8 cells for each 16V battery and charge each battery from an 18 to 20V supply, but i think that's more expensive and complicated than what the OP is trying to accomplish. another way to power this off of a single 12V battery would be to get a DC-DC converter with a 12V input and +/- 16V outputs (you might find +/-15V ones on the market), but i think the OP is not wanting to spend that kind of money either...

 

[audioguru]

Amplified computer speakers are small so they have no bass frequencies. Their power is also small at about 1W each at clipping.
My computer speakers are much better than the average junk because they use 3" drivers with a rubber surround, huge magnets and fairly large enclosures. Their power at clipping is about 3.5W each RMS. They run off a 12VDC/1A wall-wart.