mp3 plug in speaker audio amplifier circuit

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annoyin_kid

Member
hey guys its me again. anyway i went to school and we were given a new project. it is something related to the issue "safe and secure". i decided to make a mp3 plug in speaker audio amplifier circuit. it is a speaker that plugs into the mp3 instead of headphones. i got the plug bit and soldered wires to it, then i amplified the signal through a single transistor (bc548) and the speaker i am using is powered off a different power source. then i connected the plug bit to a small radio and tried it out. at max volume there is considerable distortion and it isn't very loud. i listen to hip hop and rap and this music has lots of bass which increases the distortion.

how would i decrease the bass of the output signal to decrease the distortion and still amplify the signal to make it louder? for the amplification should i use a darlington pair or is there some kind of special transistor that does the job?

is there any other way to make what i want without messing around with the bass and treble levels?

ak
 
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Grogster

Senior Member
As far as I can tell, this is not PICAXE related, however, a simple NPN amplifier stage will not have the aplification to drive a speaker with anything other then ambient sound-level(quiet, in other words).

The audio distortion is because you are over-driving the transistor and it is clipping severely.

My suggestion, would be to buy a cheap amplifier kit from any electronics store which sells electronic kits, and build that.

This will have the advantage of it being a tested design, and should work with no problems.

Designing a discrete-transistor amplifier requires a fair bit of knowledge, and would involve much more complexity then a single 548 stage, to acheive any kind of distortion-free volume.

Generally speaking, many transistor amplifiers are still based on the class-B arrangement, with an NPN and a PNP transistor both driving the speaker - the NPN drives the speaker for half of the signal, and the PNP drives it for the other half.

You can also use darlington transistor output stages in an amplifier like this, but it has to be done right - plopping a darlington transistor into a circuit designed for a 548 or similar, would most likey cause even more distortion(due to the gain of a darlington transistor over a normal small-silicon one), and in extreme cases, could cause the darlington transisor to self-destruct, due to the current flowing through it...

Not sure if that helps at all, but my original suggestion(of buying an amplifier kit) still stands - there are many many amplifier kits, which range from very cheap LM386 based ones, to top-of-the-line kits that produce very good sound indeed(although these kits can cost hundreds...)
 
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Grogster

Senior Member
ADDITIONAL: If the speaker you are using, already has an amp in it, what you really need is a pre-amp. These can be had in kit form too, ranging from a basic one using a couple of transistors and a handful of other parts, to fully Hi-Fi ones using IC's like the LM833, incorporating Vol, Bass, Treb and Bal controls.

 
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Dippy

Moderator
Dear old AK.

As Grogster says, this is a PICAXE forum. And whilst the generous people here will give their time freely for hints/suggestions for PICAXE related problems, its not for sorting out your various non-PICAXE school projects.

With the greatest respect, you really should try other forums for non-PICAXE related problems. Or you could get a book?? And learn? Sorry, I swore.

Its not a oh-my-radio-doesn't-work-I-can't be-bothered-to-think-lets-try-the-PICAXE-forum-some-sucker-on-there-will-sort-it-out type forum.

PS. And if you cunningly start posting that your PICAXE controlled amplifier is distorting we won't believe you :)

But, nonetheless, good luck with your project. I'm sure it'll turn out fine.
 
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annoyin_kid

Member
ah dippy you got me wrong, i only posted this because i posted for help here quite a few times before and i didn't want to change forum and i did ask a couple of questions unrelated to picaxe on this forum and i got replies so i thought this was a picaxe/electronics forum.

anyway i just needed a starting point and grogster gave me that so ill be off.

oh ya bgrabowski apperantely i can build a go kart as long it is electronics related and as long as it is justified.
 
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toxicmouse

Senior Member
AK, maybe if you wanted a picaxe solution to plugging the mp3 player to a speaker via, say, a hamster, then you would receive more replies. other pets may also work... otherwise i think a kit is perhaps the most productive way forward for your project. good luck.
 
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james1

New Member
I have tried this before with a single transistor, resistor, capacitor and 8ohm speaker, and found the same thing happened. And it was just as loud as using headphones. You could make a two transistor amp from the Dick Smith Funway into Electronics Volume 1 book. Here is the site: <A href='http://www.dse.co.nz/cgi-bin/dse.storefront/45d51aeb00c0dba0273fc0a87f330716/Product/View/B2600' Target=_Blank>External Web Link</a>

Edited by - darthtader on 16/02/2007 03:01:19

Edited by - darthtader on 16/02/2007 05:13:59
 
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Rickharris

Senior Member
A quick search for audio amplifier will show you there are lots of dedicated IC's out there suitable for your requirements - This is an easier way than batteling with Transistor amplifier theory.

 
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