Sorry if this isn't 100% relevant, but what does the 10uF capacitor do in the "microphone input" circuit?

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Hi Digitan,
The 10uF cap across pins 1 and 8 0f the LM386 boosts its gain from 20 to 200 so it is sensitive enough for a microphone.

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Uncle $crooge

 

i find the silver stripboard better, even with this iron, i can make good joints, its almost as if the solder is attracted to the tracks whereas on the other one it seems attracted to the tracks and the other strips!!! this could be because i dont sand it to remove any grease or that it is at least 8 years old!!!!

 

i was looking for something simple like this: http://www.st-andrews.ac.uk/~www_pa/...rt1/page2.html (fig 1.5 on the left) i tried it but it didnt work, the red LED came on but none of the others, the red is the most sensitive (probably because it needs slightly less voltage than the others)

 

also, the transistor was getting hot

 

The transistor buffer that was shown is an emitter-follower that doesn't have any voltage gain. It has voltage across it and current through it and its heating is that voltage times that current.
If you used a current-limiting resistor in series with the LED to protect the LED from burning out, then the transistor did nothing. Connecting the LED and its series resistor at the speaker would have lighted it the same.

How did you connect other LEDs?

Didn't you use a resistor in series with the transistor's base to limit its current?

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Uncle $crooge

 

i did that circuit as shown, the LED's are all connected together, there is no current limiting resistors in series with the LED's because there is no current to limit!! lol i didnt have a resistor to the base, but it didnt work without it so it shouldnt work with it should it?

 

The transistor is shown as an emitter follower but you said earlier that you connected LEDs to its collector instead of to its emitter. Why?

You don't say how you connected the LEDs. In series? In parallel?

If there is enough voltage in the circuit for the LEDs to function then they or their driver will burn out without having current-limiting resistors for them.

The base-emitter junction of a transistor is a diode that always needs a current limiting resistor. If it is connected as an emitter-follower then the emitter resistor limits its base current.

It is very confusing to talk about your circuit without seeing its schematic with a supply voltage and parts values. Please attach its schematic so we can recommend how to fix it.

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Uncle $crooge

 

the LED's are in parallel

With the resistor there, they don't work at all
Here is the diagram: (havnt got schematic for the amp but am trying to get hold of it)

Thanks,
Mike

 

You can't connect LEDs in parallel, their forward voltage requirements are different. They should each have their own current-limiting resistor or be connected in series and in series with a current-limiting resistor.

Then the circuit doesn't have enough voltage. The transistor should be used to amplify the voltage, not just follow it.

The amp's schematic is available from the web if you say what it is.

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Uncle $crooge

 

Your little amp is probably designed for an 8 ohm load. If your 4 speakers are each 8 ohms then the four of them in parallel is only 2 ohms, which is like a short to your poor little amp. You are lucky it wasn't destroyed!

I have used the schematic of an LM386 1/4W amp that is designed for a load of 8 ohms. I connected the speakers in series/parallel so they are a 8 ohm load to the amp.
I have connected a transistor with a current-limiting base resistor and a sensitivity control. The transistor amplifies the output of the amp.
I have connected the LEDs in two series strings, with a current-limiting resistor for each string.
With a brand new 9V alkaline battery, the LEDs will glow with a max current of about 24mA. The amp and LEDs are a heavy load for the little 9V battery so its voltage will drop fairly quickly causing the amp to distort and the LEDs to dim. The little battery won't last long.

Attached Images

little_amp_with_leds.png (19.8 KB, 516 views)

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Uncle $crooge

 

thanks, will try that.. i have a rechargable battery so i dont need to keep buying new ones.

so, up to the 470uf cap is the amp is it? so i just need to add the speakers, led's (& resistors), transistor and the pot?

Thanks, Mike

 

A little 9V rechargable battery is only 120mA/hrs at only 7.2V, so the circuit will play music and blink the LEDs for only about 4.8 hours.
If it is turned up too loud (from only 1/4W?) so the amp distorts, and the LEDs are on most of the time then the rechargable battery's charge will last only 1 hour.

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Uncle $crooge

 

i use the computer's usb aswell sometimes, this works fine, i just connected a pp3 battery clip to the + and - wires, most of the time i use headphones, so i will charge the battery every night and leave it on overnight.

Thanks for the help
i'll let you know how i get on

 

that worked thanks but ive now got another one and wish to insert bulbs into my speakers (behind the cloth so it shines through)

so, i connected the i/p and 1 red LED to the o/p with no current limiting resistor, the mp3 player was on full volume and i only got flashes of realy loud beats (not all songs worked) but when i connect my multimeter (set to diode test) it goed brighter but still flashes to the music, could i just add a battery in parallel to the LED because that is like what the multimeter is doing isnt it?

EDIT: i am not using speakers this time, just the LED's
Thanks,
Mike