in need of a really simple audio amplifier

[gearhed31]

ok, so im going to start off by saying i know very little about electronics. im a mechanical engineering student so i know the physics of electricity, but thats about it. i have an old set of speakers from a home audio system, but they need an amplifier badly. how hard is it to build one? (i can solder and make circuits, i just need to know whats necessary) also, this may sound kind of wierd and stupid, but could i substitute a relay for the amp, using an external power source to run the speakers and the audio signal from my laptop to activate the relay, would that work

 

[davenn]

Hi there
welcome to the forums

well its not easy!! but for some one with little experience like yourself it will be a good challenge
A relay is a switch, NOT an amplifier

You dont say what country you are from ?? there are a number of kitsets available from various hobbiest electronics suppliers that would make life a lot easier for you.
You will still have the dangers of working with a Mains AC voltage to a low voltage DC power supply. This has to be considered an undertaking that would need some trained supervision to make sure you dont kill yourself or others that may use your amplifier

Dave

 

[CocaCola]

There are a lot of kits out there that run off reduced voltage, and thus could use a wall wart making them a much safer option for the hobbyist... Look into 12 automotive amplifier kits and look at a decent power supply or even a laptop power supply to run them... Read the datasheets of the chips, most automotive chips can take many more volts than 12 so you have a few more options on the 14-20V laptop power supplies for example...

The Ramsey UAM2 is a nice kit that works well for a DIY one, I like it because of it's low heat generation vs others that get quite hot... It's Mono so you will need one for each speaker, low heat means it can be installed in the speaker enclosure... Give it 8-18V and you will get sound...

 

[gearhed31]

with the relay thing, im most likely wrong, but couldn't a speaker be run like a turn signal on a car, a small, intermittent signal (the audio signal) gets sent to a relay which then turns on and off in sync with the source, sending power out? a speaker just recieves a series of electric pulses right? again, i know little about electronics, i know the basics, and i know how to wire the electrical system on a car, and i know what is taught in physics 101. im from the US, by the way.

 

[Harald Kapp]

A speaker converts an electrical signal in the range 50 Hz... 20 kHz (give of take a few Hz) into an audio signal.
A car's turn signal has a frequency of maybe 2 Hz or so.
You see the difference and why a relay is not suitable?

Follow the suggestions and get a decent kit.

Harald

 

[gearhed31]

oh ok, so basicaly a relay couldn't turn on and off fast enough, right? thanks for the info, ill look into a kit

 

[davenn]

oh ok, so basicaly a relay couldn't turn on and off fast enough, right? thanks for the info, ill look into a kit

how fast a relay can turn on and off is irrelevent for an audio amplifier
it ISNT an amplifier, it isnt going to boost signals for your laptop, mp3 player or anything else.

knowing about car electrical systems is a long way from working on a stereo audio amplifier.
We are all here to help, but you need to listen to and understand the good advice given to you

cheers
Dave

 

[Harald Kapp]

@dave: If his relay is fast enough, he could build a class-D amplifier

 

[Harald Kapp]

@gearhed: Nope, just kidding. There is no relay that fast.

 

[Rusty]

If you want to make a good audio amplifier with little noise and no distortortion, you will need a lot of pations and skills for this. Especially when doing it in stereo mode. I would do like suggested above, get a kit and start from there. Will save you lots of work and time. Chip amplifiers are very easy to use :

Meanwhile.. When you wait for parts and when you start the project: Always study the circuit, try to understand the components, different technics and other theory in the amp. This is the best way to learn electronics.

If you really want to learn audio amplifiers, buy the books by Douglas Self

 

[BobK]

a speaker just recieves a series of electric pulses right?

No, a speaker receives continuously varying voltage, not a seried of pulses.

Bob

 

[KJ6EAD]

Gearhed31, what's the wattage rating and impedance of the speakers and how loud do you want to get? Do you care about tone control (equalization)?

As a mechanical engineering student, you might like to do some math regarding the opening and closing of mechanical relay contacts and the movement of the armature 20,000 times in a second. Even if you disregard all of the other electrical and thermal issues, the physics alone should prove to be...problematic.