project help with toy IC boards

[CALAHAN]

Hi,

I am new here, and I am not very experienced with electronics. In fact, I am just learning. I am not good with message boards either.

I have a few pet projects I want to get through, and that is is far as I will need to go electrically. My biggest issue is this; I have removed a POC board with two sound effects from a toy, placing it in and splicing it into the power supply of another toy. The original toy worked off of two AA's, and the new one off of two AAA's (no issues there I don't think except for possibly amperage right?). The sound effect from the original toy is not quite loud enough. It works , but I need a bit of a boost in volume. I also have little room to work with. The speaker is probably  8 ohm.

I have been experimenting with the 386 op amp. I created a breadboard circuit and the amplifier works with the toy IC board running through it. However, the IC board requires 3 volts, and the 386 does not seem to want to sound good on anything other then 9 volts. How can I split the 9 volt to run both of the devices at once?  Again, I have little space to work with. I may not even be able to fit the op amp and it's few capacitors in the shell of the toy. I may have to look to one of those "Simple 1 watt amplifier" utilizing that odd named transistor.  I tried powering the op amp off of a little thin 12 volt battery I bought that supposedly powers the key chain activated on/off car alarm systems. The op amp was not as loud as it is with the 9 volt, and the sound was a bit distorted also.

Another situation I have is that I have created a sound effect by using a Radio Shack message recorder. It needs 9 volts, but again is not very loud. The Op amp needs 9 volts to run also, so how can I power both of these with the least amount of batteries? Can I use one 9 volt for both?

See what Mean, I am way behind you all here on this board.

Thanks for any help,

Bruce

 

[audioguru2]

Use a 9V battery so the LM386 power amplifier drives the speaker loud enough, then reduce the voltage to 3V with an LM317L adjustable voltage regulator. The LM317L is small and needs just two small capacitors and two resistors. The ratio of the resistors sets its output voltage.

The message recorder and the LM386 can both be powered by one 9V battery.

 

[CALAHAN]

Hi,

I'll look into the LM317L. Perhaps I can do a search on the net to get a wiring diagram of how to connect the capacitors and resistors. Hopefully there is room for the parts in the toy.

Can I create a 9 volt split to 4.5 volts and use the split for the chip but yet patch off the ful 9 volts that passes the resistors for the split? I think the chip will run on 4.5 without frying it. Would this work?  - giving me the 4.5 volts needed for the chip and the 9 for the op amp at the same time?


As for powering the message recorder, (in my second project mentioned initially), and the LM386 both off of one 9 volt battery, I tried this and I only get a hum out of the speaker. What's the sercret to get it to work?


Thanks,

Bruce

 

[audioguru2]

If you don't want to use an LM317L voltage regulator, you could make a voltage divider with two resistors then use a transistor as an emitter-follower to buffer the voltage and feed it to the 3V chip. The resulting 3V won't be regulated so it will drop as the voltage from the battery drops, but it is cheaper.

Maybe your LM386 amp causes hum because you are not using shielded audio cable for its input. So your wires are picking up mains hum. Or maybe your battery doesn't have a bypass capacitor across it so its voltage is bouncing up and down.

 

[CALAHAN]

With the transistor idea, what kind of transistor, and what value resistors?

I got the Radio Shack chip and the 386 to work off of one 9 volt, the there is no amlification anymore.

Bruce

 

[audioguru2]

Just make a voltage divider with two resistors so the junction is 0.7V higher than the 3V output wanted. Then the transistor is an NPN and is connected as an emitter-follower with a 3V output when the 9V battery is new. A 2N4401 has high gain and a high max current.

You don't sketch how you connected the message recorder to the LM386 amp so I have no idea what is wrong. The LM386 has a gain of 20 which should be plenty. Maybe the recorder's output has a DC voltage so needs a coupling capacitor to the amp.

 

[CALAHAN]

I'm sorry, I guess I shouldn't have proposed this idea here becaue this is way over my head. I don't meet the minimal knowledge for this stuff. Everything I do I have researched on the web looking for schematics and reading. I understand where you are going, but I do not know any of the values of the transisors, or resistors needed, or where to wire them up. I guess I need a schematic.

I'll make a sketch of how I wired my two projects at work tonight and post it later. Perhaps one of you guys can figure out how I can pull this off while taking up the least amount of space inside the toy as possible - if it can even be done.

Bruce

 

[CALAHAN]

PROJECT 1: I attempted to trace the circuit board for the toy sound effect IC, but my eyes just can’t handle it. I tried to re-create the colors of the resistors as best I could. This configuration does amplify. However, I have to use one of the pots or trimmers (whatever it is – variable resistor?) that I bought in a Radio Shack mixed bundle package. This one happens to be printed with the 10k  341 on the side. Any other setting except for wide open is distorted. Through an 8 Ohm speaker it is loud, and a touch distorted. I am unable to turn the pot down, because it distorts.  When using the 16 Ohm speaker it is even louder but not distorted. This board will have to be fitted with an 8 Ohm because of size restraints. Removing the 10 uf capacitor from pins 1 and 8 is not loud enough. The other issue with this configuration is that the op amp needs 9v and the IC needs 3v. I need to power both off a 9v, or comparable sized source. 

PROJECT 2: this set up is basically the same as before. In this trial I kept the 10 uf capacitor in place between pins 1 and 8. The 10k trim pot was retained, but better luck was gained from a different one, which was unlabeled and has since broken. I was finally able to get amplification from the 386 with powering both devices off of one 9v. However, after some time, I could smell something melting and the IC board’s LED remained on and quit working. It must have fried. I checked for shorts but there was none. In this application I would need to figure out how to get the clearest amplified sound from the 386 (if it doesn’t burn the IC board again!). I assume that if I could figure out what the resistance the pot is creating for the best sound, I could buy an equal resistor to match it. This requires, I would suppose, reading a multi-meter – something I have not been able to figure out at this time.

This project has cost me quit a bit of money at this point, and has been very discouraging, especially after I smoked the Radio Shack recorder. As can be seen, I am very new to this field, and though I understand the principles, I do not know how to wire a voltage splitter, or what types of parts/values, I need to buy. I’d be willing to pay someone to solve these issues for me by drawing up a wiring diagram.

To accommodate the small amount of space I have for Project 1 - I purchased a “Simple 1 Watt Audio Amplifier” kit from a company out of Connecticut called SCI-TOYS. This utilized a MPSW45A Darlington transistor, two 100,000 ohm resistors (brown, black, yellow, gold), one 10,000 ohm resistor (brown, orange, and gold), and a 50 ohm resistor (green, black and gold). The only problem is that the company shorted me on one of the 100k resistors, and the 50k had a different variation of colored bands so I don’t know what value it is. Henceforth, I could not see if the thing worked as specified. I tried substituting the 100k resistors with a few extra 10k I had, and the volume was lower then the original sound effects. I understand that this kit is splitting the 9v power supply to feed the transistor at 4.5v. But again, this didn’t work for me, and I am running out of patience. If anyone can help, I’d appreciate it. It took me a few hours to draw this up to better explain my two projects.

Thanks,

Bruce   

View attachment 39763

 

[audioguru2]

Your sketches are good, but don't show how the 10k volume control pot is wired. I have sketched how it should look.

The LM386 must have 0V on its input. The circuits are probably feeding DC to the pot and LM386. Therefore a 0.22uF input coupling capacitor is needed to feed audio to the pot and to the LM386 but block the DC.

The LM386 power amplifier needs a resistor and capacitor in series connected to its output as I show.

Every battery powered circuit should have a 100uF capacitor across the battery as I show.

Maybe the recorder blew up because you had the pot connected wrong and it shorted its output. The center terminal of the pot should connect to the amplifier's input, not to ground. Then the output gets a constant 10k resistance not a variable resistance which includes a short.

The 10uF capacitor between pin 1 and pin 8 on the LM386 increases its gain to 200 and is not needed in your application.

View attachment 39764

 

[audioguru2]

I forgot.
Disconnect the black speaker wire of the sound sources from the ground of the amplifier. maybe they have DC on them. Connect together the negative battery wires instead.

 

[CALAHAN]

Guru,

I don't understand what you mean about connecting the battery negatives together and discionecting the original IC speak negative. Where does the speaker negative go then?

I tried your diagram. The only thing I don't have is the .047 capacitor. Perhaps the pot is bad because I didn't get any amplification out of it above the normal volume, and as I tried to turn it, I got nothinmg but variable volumes all with distortion. This is of course for the toy chip, not the Radio Shack chipcorder because that is fried. Is there anyway of eliminating the pot? I don't really want it. And is the .047 capacitor necesary? It's just a filter isn't it?

Bruce

 

[audioguru2]

Your volume control pot is intermittent and is brobably burned out from being connected wrong. It is probably needed for you to reduce the volume to avoid distortion.

We don't know if the IC has a DC output which will mess-up the operation of the pot and the LM386, so the 0.22uF capacitor was added to block DC.

The datasheet for the LM386 shows the 0.047uF capacitor and the 10 ohm resistor in series at its output to avoid high frequency oscillation which causes distortion and quickly drains the battery.

I modified your sketch showing the IC negative speaker wire disconnected and the two negative battery wires connected together instead.

View attachment 39766

 

[CALAHAN]

Guru,

O.K. but in this case, I was powering both off of one battery. So I just connect the battery wires from the IC to the positive and negative of the breadboard which has the 9volt battery at the other end?

Bruce

 

[audioguru2]

The circuit in the toy is designed for only 3V. 9V will probably destroy it.
If you can get it working properly with its own 3V battery like on your sketch I fixed, then I'll show you how to reduce the 9V down to 3V.

 

[CALAHAN]

Well I hooked it up, and it does seem to amplify. It is a bit distorted, but I guess I'll have to live with it. The .047 capacitor comes in both a plastic green design and the usual ceramic disc. Any difference? I bought two new pots - one 100,000  and one 10,000. Both create a bit of distortion. I tried two different speakers also - and it is the same. The issue I have is that now with all of these capacitors, I don't have room. In any case, can I get the schematics to create the 9 volt splitter to 3 volts and see how that works?

Tomorrow I will buy a new Radio Shack chipcorder and see how that works on this 386 schematic you posted above.

Bruce

 

[audioguru2]

Well I hooked it up, and it does seem to amplify. It is a bit distorted

The LM386 has fairly low distortion up to clipping. Maybe the 0.047uF capacitor will reduce yours. Maybe the distortion comes from the toy.

The .047 capacitor comes in both a plastic green design and the usual ceramic disc. Any difference?

It probably doesn't matter since the frequencies aren't high frequency radio waves where ceramic disc capacitors are needed.

I bought two new pots - one 100,000View attachment 39778

 

[CALAHAN]

In reference to the distortion, is there something I can put in place of the pot that would keep the input from what I assume is overdrivng the 386?

With this 3.3v splitter, can I still run the 386 off the 9v while also tapping off the 3.3v?

Thanks,

Bruce

 

[audioguru2]

In reference to the distortion, is there something I can put in place of the pot that would keep the input from what I assume is overdrivng the 386?

With a 9V supply (a brand new battery), an LM386 can provide 450mW of power to an 8 ohm speaker with low distortion. If the volume control is turned up higher or if the input signal becomes louder then the output will clip and become very distorted for the louder parts that are clipped off. Just keep the volume control set to below clipping.
I think the sound from the toy is distorted because its circuit is cheap. Then the sound is distorted at any volume control setting.

With this 3.3v splitter, can I still run the 386 off the 9v while also tapping off the 3.3v?

Yes.

 

[CALAHAN]

What do you think about this UTC KA8602 as an audio amplifier?

Bruce