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My 12 watt x2 stereo amplifier

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Hey ppl I'm ben and finally built my first proper amplifier, which is just built into a plastic jiffy box, with a 10k double gang pot for vol and runs off of a 2.2Ah 12V SLA battery, the amplifier modules im using are made by KEMO in germany, i picked them up for AU$23.95 each here, all up the whole thing costed AU$107.38 to build including SLA battery (AU$24.95) and charger ($19.95)
i have it in my school bag along with a wooden box containing 2 x 4 3/4 inch woofers and 2 x 2inch tweeters, i just hook my mp3 player up to the amp.
it has RCA inputs, speaker spring terminal outputs.

it sounds great btw, the modules need a bit more burning in but once thats one it will be mad.

here are some pics

top of amp

front of amp

rear of amp

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Hi Ben,
Your amplifier looks nice and looks identical to the 2 x 5W amplifier I made for the beach many years ago. Mine used a 7.2V Ni-Cad battery (inside its case) and its bridged amplifier ICs produced 5 real Watts per channel at low distortion into my 4 ohm speakers.

Are your Kemo amplifier modules the ones in my pic? They are 12 Whats, not Watts.
Their power is 6 Watts continously at low distortion into a 4 ohm speaker with a 16V supply. With your 13.2V battery the power is 4 Watts into a 4 ohm speaker or 2.2 Watts into an 8 ohm speaker.

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Hi Ben,
There are lots of bridged amplifier ICs made for car radios that produce 14 real Watts per channel continuously with low distortion into a 4 ohm speaker with your 13.2V battery powering them. About 7.5 Watts into 8 ohm speakers per channel.

A TDA7240A is a single channel bridged amplifier. The datasheet has a pcb layout for an amplifier.
A TDA1554 is a two channels bridged amplifier.
Lots of kits use them.

What is the impedance of your speakers?

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heres the full specs

Modules: KEMO #M32 12W ampl modules x 2
Pot: 10k linear double gang
Input: stereo RCA
Output: Speaker wire spring terminals
Battery Voltage: 12 - 13.5v DC
Batt max amps: 2.2Ah

Speakers: 4 3/4" Sharp woofers and 2" Sharp tweeters
Impedance: Woofers 8 ohm, Tweeters 6 ohm.
Box: Particle board, used to be an old speaker box, used to house one of the woofers and one of the tweeters. Other box was destroyed!

Soon to come

5" 4 ohm 2 way car speakers

I will get a pic of the enclosure soon
they are in the same box but there is a divider between the 2 sets, so that way they aren't cancelling each other out (which was happening)
im going to put a 1 inch port into the back of each section, to put relief on the speaker cones and to aid the bass reflex.

i will add more pics soon

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Hi Ben,
Stereo speakers in the same box cancel the bass frequencies when they are connected "out of phase". When they are connected with the same phase then the bass is very strong without any cancellation.

The size of the box must match the spec's of the woofer for good bass:
1) If the box is too small then the low bass frequencies will be missing and the upper bass frequencies will be boomy.
2) If the box is too big then the low bass frequencies will be missing.

Only some woofers produce better bass when the box has a port to make it a bass reflex. Then the diameter and length of the port must match the spec's for the woofer and the size of the box for good bass.
A ported box for bass reflex is usually bigger than a sealed box for good bass.

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  • 2 weeks later...

in reply to audioguru, you say that my amps deliver less than specified, it does have a bit of high volume distortion, but it is quite a bit louder than 2.2 watts could make.
my estimate about 4 watts per channel, without being optimistic
in regards to the amplifier u had, what kind of inputs and speaker outs did you use, i was going to use banana plugs but thought it would be stupid, plus this had to be a budget amp, so i just used speaker spring terminals and they work fine!

im going to make a smaller box and use 5" 2 way 4ohm car speakers, so that way i save space by not having a seperate tweeter, and get more power out of the amp by having a 4ohm impedance. and i can make a storage space for the amp and battery so it is all in one box.

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Hi Ben,
I had some small 2-way speakers in cast aluminum boxes. I upgraded their 4 inch woofers for better 4 ohms ones. Then I added ports that were tuned to 75Hz. The boxes were a little small so I added some bass boost to the amplifiers. I made a clipping indicator circuit so I could see distortion when the battery was running down.

Don't make your box smaller than is recommended by the speaker manufacturer or the bass will be missing at low frequencies and will be boomy at higher frequencies.

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yeah i know what you mean, im not too fussed on SQ, it just has to relatively clear, not distorted and loud.
Car speakers dont have a specific enclosure requirement, as they are usually mounted in car doors.
i would use the box i have but the way i have built the bottom has been built around the existing speakers, plus im going to make the next one from scratch
i use it at school to play music at lunchtime and that (got told by one teacher never to bring it again haha, but the rest love it, so f*** her!!!


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