building a 2.1 amp some advice needed :)

[stormrazer121]

So after trolling through this forum looking for information and doing research after research on parts and ICs and how it all works, and finally making my own little circuit i feel pretty confident enough to make a 2.1 amp to incorporate a sub into my next project

But something i do not understand is how i would do this, i have a number of ICs hangin about, one which just happens to do just that is from a board i pulled apart, its part number is,
4558d jrc sum 6b29w, there is 2 other ICs on the circuit but im sure this is the one for the amp,

However i understand how to make a normal mono amp and how to use two to make a stereo setup but something i do not understand is how i would convert one to drive a small driver as a "sub" only small but i only need small as it is a tiny setup with 2" 4 omh 2watt speakers, Hench the need for a sub as there is no bass at all.

So does anyone any advice on what i could do to make only low frequency be sent to the sub? thanks

P.S - i learn t how to read diagrams so if you have one i can look at i should be able to read it and work out what i need to do thanks guys

 

[ChrisP58]

The 4558 is indeed an op-amp. A datasheet can be found here:

You will want to setup an op-amp as a "low pass filter" to limit the signal to the bass amp to only low frequencies.

A good article on op-amps can be found here:

 

[audioguru]

The 4558 is a very old dual opamp. It cannot drive a load lower than 2000 ohms so it cannot drive a speaker.
Its minimum recommended supply is 10V or plus 5V and minus 5V.

 

[stormrazer121]

Okay, more so then using a already setup chip in my case, 8002a md1227 how would i be able to change this so that it only put out the frequency i need? as it stands it will drive a speakers as a normal mono output would, i just need to stop that and make it drive a small sub.

 

[audioguru]

We do not know what your 8002A is. Analog Devices datasheet says it is simply a dual high frequency video amplifier that will not drive a speaker.

You need a little audio power amplifier IC to drive a little woofer. The audio amplifier IC will have a datasheet so we can plan a lowpass filter for it.
What supply voltage will you use for the woofer power amplifier? How much output power do you need?

 

[stormrazer121]

ok, sorry about that i started talking about anouther which i have without even mentioning it!, the one i will be using is a 8002a md1227, this is the IC that is currently used to power a speaker.

The supply voltage will be from USB power so thats what approx 5v? i might not understand this stuff completely but i fully understand how to put it all together

- p.s i just looked back and i did mention the 8002a md1227 which is working in my setup amp there is also another IC on there 8002a md1223q but this IC is connected to the right side, one for the right, one for the left?

 

[audioguru]

None of us can find any info about the 8002A IC.
With a power supply that is only 5V then a single-ended linear power amplifier has an output of only 0.14W into an 8 ohm speaker which is almost nothing.
If the speaker is 4 ohms then the output is about 0.24W which is also almost nothing.
Maybe it has bridged amplifiers. Then the power into 8 ohms is 0.5W like a cheap clock radio.

 

[stormrazer121]

I have no idea, all i know is the this chip was pulled from one of them el cheapo i docks, works fine for normal stereo mind! i have managed to get my hands on a 2.1 amp board, which does work only problem with this is that the remote controls the bass, if i took a picture of it and named the ICs on it would it be possible to rewire any of it to allow me to control the bass with a potentiometer?

 

[audioguru]

You do not have a chip, you have a chip with many other parts on a circuit board.
Many products use custom-made ICs that do not have a datasheet. If yours has it then we cannot help you unless you post its detailed datasheet.

 

[stormrazer121]

Okay i understand what your saying. Sorry I'm really new to this so still learning despite my enthusiasm to learn it is rather difficult to understand, could you suggest a good chip to start with? One that has a data sheet and a schematic i can follow for mono sound i guess? As from what i can tell is that if i use a 8 pin IC this is able to be used as mono sound correct? and i would use two for stereo sound?

 

[Nigel Goodwin]

Okay i understand what your saying. Sorry I'm really new to this so still learning despite my enthusiasm to learn it is rather difficult to understand, could you suggest a good chip to start with? One that has a data sheet and a schematic i can follow for mono sound i guess? As from what i can tell is that if i use a 8 pin IC this is able to be used as mono sound correct? and i would use two for stereo sound?

Essentially so - but for a 2.1 system you need a decent size sub-woofer, and a decent powerful amplifier to drive the sub (left and right can be smaller amps).

 

[stormrazer121]

Well, the idea is to build a small dock with 2.1 which means i don't need anything fancy, for arguments say i have 1 that unfortunately is unusable for this project but it only has a 14 x 4 x4 watt setup i don't even need that much power! so ye a tiny 4" sub would work great with 2" for left and right, at least they are what i have and intend to use.

 

[audioguru]

Some car radio amplifier ICs have two amplifiers for stereo. They have more pins than 8 and do not work from only 5V.

Since your power supply is only 5v then the output power from an ordinary amplifier will be low.

A TDA2822M is an amplifier IC with 8 pins that can work from a 5V supply. It has two amplifiers inside. Digikey has 1700 of them in stock today.
As a stereo amplifier it produces 0.25W per channel into 8 ohm speakers. Very low power.
Both amplifiers can be bridged together then the mono output is 0.9W into 8 ohms. Maybe this will be loud enough for you.
The datasheet has pcb designs.

My little computer speakers use a 12V supply and produce about 3W each. They sound pretty good and play fairly loudly when directly in front of me.

Here are schematics of the TDA2822M stereo amplifier and the bridged amplifier:

 

[audioguru]

I have built many amplifiers and speaker systems.
I recently bought a Sylvania 2.1 powered speaker system for $24.99 as a "special buy" at a local store. It sounds great, looks good and is fairly loud. I use it for the TV in my computer room and the digital cable TV converter also plays many FM radio stations.

In the ad it says 150W. On the box and owner's manual it says 75W RMS. On the power label it says 75W (so it is 100% efficient!). Inside it has a small power transformer labelled 9VAC/1.1A (9.9W). The amplifier is probably 50% to 60% efficient but might be a modern class-D switcher that is 90% efficient.

Its amplifiers are two 16 pins DIL ICs with a small heatsink glued on.
One IC is probably a stereo amplifier feeding 1.5W to 2.0W real Watts to each 4 ohm satellite speaker.
The other IC is probably bridged and feeds 4.0W to 5.0W real Watts to the 6 ohm sub-woofer.
So the total output power is 5.5W to 7W.

Each satellite speaker has two 1.5" 2 ohm speakers with foam surrounds and the "soft-dome tweeter" is not a speaker but is actually a vent covered with a soft dome.
The sub-woofer is a 5" long-throw speaker with a foam surround in a pretty big wooden ported enclosure. It lights up with 6 blue LEDs.

The amplifier and power supply are built into the sub-woofer enclosure and has a volume control and bass and treble tone controls.

I have played it loudly for hours and it doesn't smoke. I have never heard its amplifiers clipping. I tested its frequency response with my 67 years old ears and it plays from 40Hz to 18kHz smoothly and very well.

 

[stormrazer121]

Very informative thanks i guess the little dock i made must be pretty weak then, i am actually able to provide it with more power but using USB is just convenient i am just not sure about transformers and really dont want to mess about with something that could kill me if i did it wrong so reading up and learning about them is on my to-do list at the moment!

Currently I'm eyeing up the schematic and really do need to understand the IC side of things more, struggling to read it correctly due to my novice skills ha! thanks though very helpful!

 

[audioguru]

i am just not sure about transformers and really dont want to mess about with something that could kill me if i did it wrong!

Simply buy an AC-DC power supply that plugs into the electricity. They have many voltage choices available and they are safe.