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Turning computer speakers into portable mp3 amplifier. Problem.

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bulipap

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Hello,
I'm trying to make a portable mp3 amplifier out of two computer speakers. Now I have read this article on how to make them:
https://www.instructables.com/id/ho...-power-connector-and-removing-second-speaker/
Also, here's a picture of my amplifier, battery pack and speaker: https://imageshack.us/g/163/img2012t.jpg/
I'm stuck at step 3 where you should add the power source (in my case a compatible battery pack). I have the battery pack and want to either solder it directly onto the board or connect them with the two wires that I cut from the power transformer. Where do I solder the two wired to the board or which two wires from the battery pack should I connect to the two wires from the old transformer? In other words, how do I connect the battery pack to the amplifier?
I know, the explanation wasn't the best but I would be really glad if you tried helping since I have had this problem for a long time now already...
Thanks!
 

the article is kind of quick and dirty guide, it ignores the fact that a 9v ac voltage is rectified with a full wave bridge to about 12.5v DC, in addition it recommends to connect the 9v battery in place of the transformer which means that you will have an additional 1.5v drop as the 9v go through the bridge rectifier to enter the amplifier.
 
alexan_e said:
the article is kind of quick and dirty guide, it ignores the fact that a 9v ac voltage is rectified with a full wave bridge to about 12.5v DC, in addition it recommends to connect the 9v battery in place of the transformer which means that you will have an additional 1.5v drop as the 9v go through the bridge rectifier to enter the amplifier.
Click to expand...

Thank you for answering but I didn't really understand that much of what you just said. I mean, I'm kind of a beginner.
So to where do I really connect the 12V battery pack? (I've checked and it should be suitable for the amplifier) Also, how do I know which point on the circuit board is positive and negative to where I solder the battery pack?
Thanks!
 

If you want to do what the article describes then you connect the two wires of the battery in place of the two wires from the transformer, there is no polarity problem because the diodes that are supposed to rectify the transformer voltage will feed the battery voltage with the correct polarity to the amplifier circuit.

---------- Post added at 18:26 ---------- Previous post was at 18:24 ----------

see the two schematics Diode bridge - Wikipedia, the free encyclopedia
depending on the input polarity a different couple of diodes conduct and the output polarity is always the same.
 
alexan_e said:
If you want to do what the article describes then you connect the two wires of the battery in place of the two wires from the transformer, there is no polarity problem because the diodes that are supposed to rectify the transformer voltage will feed the battery voltage with the correct polarity to the amplifier circuit.

---------- Post added at 18:26 ---------- Previous post was at 18:24 ----------

see the two schematics Diode bridge - Wikipedia, the free encyclopedia
depending on the input polarity a different couple of diodes conduct and the output polarity is always the same.
Click to expand...

Alright, thank you! Only one more question, when I connect the battery pack to the two wires, isn't it so that I should connect plus to plus and minus to minus? Also, how do I know which one is which when both wires are blue? The wires from the battery pack are red and black so the red is plus and black is minus I presume.
Once again, thanks! I really appreciate you helping a beginner.
 

that is what I was trying to explain in the previous post, the transformer output is alternating (AC not DC), the plus and minus are constantly changing so there is a bridge rectifier on the PCB that can convert it in to a DC, these diodes will transfer the battery voltage with the correct polarity to the amplifier, it doesn't matter where you connect the + and where the - , just connect them where the blue transformer wires were.
The diode bridge are the small black rods with a grey ring which are located near the point that the blue cables are connected.
 
alexan_e said:
that is what I was trying to explain in the previous post, the transformer output is alternating (AC not DC), the plus and minus are constantly changing so there is a bridge rectifier on the PCB that can convert it in to a DC, these diodes will transfer the battery voltage with the correct polarity to the amplifier, it doesn't matter where you connect the + and where the - , just connect them where the blue transformer wires were.
The diode bridge are the small black rods with a grey ring which are located near the point that the blue cables are connected.
Click to expand...

Okay, well I didn't get it to work in any way... I guess the amplifier might just be broken then... Maybe I'll buy a new one if I find.
Sorry to bother you this much but I'm just curious, to where would I connect the battery pack if I were to solder it onto the board?
Once again, thanks for your help!
 

Did the speaker work before taking it apart or it was broken to begin with?
The most appropriate position to connect the power supply would be in the electrolytic capacitor of the diode bridge, this is directly connected in the output of the diode rectifier but a reversed polarity there would damage the circuit.
Connecting the battery in the input where the transformer secondary was connected gives you a safety net because polarity doesn't matter and is taken care with the diodes before it reaches the capacitor and amplifier supply lines, the downside is that you loose about 1.7v because the battery voltage passes through two diodes and each diode will drop about 0.7v from the input to the output.

Alex
 
alexan_e said:
Did the speaker work before taking it apart or it was broken to begin with?
The most appropriate position to connect the power supply would be in the electrolytic capacitor of the diode bridge, this is directly connected in the output of the diode rectifier but a reversed polarity there would damage the circuit.
Connecting the battery in the input where the transformer secondary was connected gives you a safety net because polarity doesn't batter and is taken care with the diodes before it reaches the capacitor and amplifier supply lines, the downside is that you loose about 1.7v because the battery voltage passes through two diodes and each diode will drop about 0.7v from the input to the output.

Alex
Click to expand...

Actually no, it worked perfectly from the beginning before I took it apart. A friend of mine actually got it to work perfectly but then the next day I, of course, had to go and experiment with it without knowing the consequences of it breaking... So I tried to connect the battery pack to the circuit board and probably messed it up. Since then it hasn't been working properly. So... I really regret that move.
Do you recommend I take apart another pair of speakers and try with that one or maybe borrow the amplifier, I don't know? Maybe buy a small portable amplifier and connect the speakers to that?
Thanks again!
 

so the speaker doesn't work anymore even if you connect the transformer as it was?
unfortunately connecting a power supply in the wrong position in the circuit can damage the circuit, this is probably why the article suggests to connect the power supply where the transformer was, to avoid damaging the circuit.

I can't really recommend anything, it is up to you but as long as you connect the battery where the transformer was and the battery voltage is not higher than the transformer voltage there is no way to damage the circuit.
Note that there are some PC speakers (this wasn't the case in your speaker) that have an external wall plugged power supply which provides DC in the input of the speakers, in that case you must be careful of the battery polarity.

Alex
 
alexan_e said:
so the speaker doesn't work anymore even if you connect the transformer as it was?
unfortunately connecting a power supply in the wrong position in the circuit can damage the circuit, this is probably why the article suggests to connect the power supply where the transformer was, to avoid damaging the circuit.

I can't really recommend anything, it is up to you but as long as you connect the battery where the transformer was and the battery voltage is not higher than the transformer voltage there is no way to damage the circuit.
Note that there are some PC speakers (this wasn't the case in your speaker) that have an external wall plugged power supply which provides DC in the input of the speakers, in that case you must be careful of the battery polarity.

Alex
Click to expand...

Okay I see. If I connect the transformer as it was it means I have to connect it to the wall, which could be a bit dangerous, don't you think?
Also, if I would try this same on a new pair of speakers and connect the battery pack to the wires of the transformer, could it somehow do damage if I connect the ends wrong (plus to minus)?
By the way, this is a amplifier, right? **broken link removed**
So if I would somehow connect the speakers and a compatible battery pack directly to that think, do you think it might work?
I am really in a need of these speakers and you are the only one who's actually helping me. Once again, thanks!
 

Okay I see. If I connect the transformer as it was it means I have to connect it to the wall, which could be a bit dangerous, don't you think?
Click to expand...
I don't think so, this is a low power transformer, what can go wrong, just close the box before powering the circuit in case a capacitor blows up :shock:


By the way, this is a amplifier, right? 60W Stereo Audio Amplifier for Car
Click to expand...
Yes the link is of an amplifier and is probably overrated but it needs a much stronger power supply, the specifications say Voltage: DC 12V, 2~5A (2-5 Amperes), you battery can't provide that


Also, if I would try this same on a new pair of speakers and connect the battery pack to the wires of the transformer, could it somehow do damage if I connect the ends wrong (plus to minus)?
Click to expand...
Instead of explaining for the fourth time that the polarity at the input of the bridge doesn't matter I suggest you read Diode bridge - Wikipedia, the free encyclopedia .
In the first 10 lines of the article it explains (and shows in the schematic) how the two polarities in the input of the bridge result in the same polarity in the output.

you are welcome
Alex
 

alexan_e said:
I don't think so, this is a low power transformer, what can go wrong, just close the box before powering the circuit in case a capacitor blows up :shock:


Yes the link is of an amplifier and is probably overrated but it needs a much stronger power supply, the specifications say Voltage: DC 12V, 2~5A (2-5 Amperes), you battery can't provide that



Instead of explaining for the fourth time that the polarity at the input of the bridge doesn't matter I suggest you read Diode bridge - Wikipedia, the free encyclopedia .
In the first 10 lines of the article it explains (and shows in the schematic) how the two polarities in the input of the bridge result in the same polarity in the output.

you are welcome
Alex
Click to expand...

Again, thank you really much for your help. I think I'll buy this one: **broken link removed** . It should just be to connect a suitable battery pack (2* 10 V aka. about 20 V battery pack I guess?), speakers, and it has a stereo audio input jack on it from the beginning. Just what I need. Rather simple also.
Is it what I think it is? Thanks!
 

Yes it is an amplifier but usually the battery amplifiers are small models intended for headphones, this kind of amplifier needs in your link needs either a high capacity battery like when you are in the car or a mains psu(unless a few hours are enough for you), I don't know what kind of batteries you intend to use and it will probably cost you to get 20v using batteries (in series) but I also doubt how long will these batteries be able to last.

Alex
 
alexan_e said:
Yes it is an amplifier but usually the battery amplifiers are small models intended for headphones, this kind of amplifier needs in your link needs either a high capacity battery like when you are in the car or a mains psu(unless a few hours are enough for you), I don't know what kind of batteries you intend to use and it will probably cost you to get 20v using batteries (in series) but I also doubt how long will these batteries be able to last.

Alex
Click to expand...

As in the following video (**broken link removed**) and reviews people have talked about, they say it lasts a few hours with about 15-20 V battery pack which they use. Some also only use 12V and it have worked great. The quality is great.
People use it for louder speakers. I think I'll try this one.
Thanks!
 

Well, I did write
(unless a few hours are enough for you)
Click to expand...
if you think it is then go ahead, you can add a mains power supply later if you want.

Alex
 
alexan_e said:
Well, I did write
if you think it is then go ahead, you can add a mains power supply later if you want.

Alex
Click to expand...

Hey Alex!
I'm just about to buy this amplifier: **broken link removed** . Now I'm wondering is it possible to add an ON/OFF switch (I have one) to the amplifier after I've connected the two speakers and the battery? If so, to where do I connect the switch?
Thanks a bunch!
 

In the schematic there is a JP2 (jumper 2) shown, it has three pins Vcc(positive supply), EN (enable) , ground.
If you connect the enable to Vcc the amplifier turns on, if you connect enable pin to ground it turns off
 
alexan_e said:
In the schematic there is a JP2 (jumper 2) shown, it has three pins Vcc(positive supply), EN (enable) , ground.
If you connect the enable to Vcc the amplifier turns on, if you connect enable pin to ground it turns off
Click to expand...

Oh I see, thank you!
So I guess JP1 is for sound control, right? As it says "gain set" in the schematic.
 

jumper1 is also explained in the schematic, it sets the gain of the amplifier.

GND GND 30db
GND VR 19.5db
VR GND 13.2db
VR VR 16db

if your input source has low signal you can use a higher gain to get the proper output power
 

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