A couple questions about some ideas I have

[Mrx3750]

Right now I'm running my computer speakers connected to a cheap pair of Sony Viao desktop speakers. Meaning I took them apart and connected real speakers to them. It works about as well as I expected, and will suffice until something better comes along. However the headphone input is noisy, poor signal to noise ratio, and I'm wondering what I can do about that.

Since the circuit board had relatively few capacitors, and all of them of some weird unknown brand, I decided to recap it earlier today. Might as well not have bothered as it didn't change a thing. I'm toying with the idea of replacing the largest capacitor, a 1000uf @ 16 volt cap, with something like a 2200uf@ 16 volt cap and see if I get cleaner sound. Should I try it?


Also I'm wondering, how would I boost the transmitting power of a walkie talkie? I'm talking about those toy ones that operate on the 49 Mhz band. I used to mess with those a lot as a kid, and I know a larger antenna helps, but what about boosting its actual transmitting power?

[ben7]

Re: A couple questions about some ideas I have

I think the walkie talkie mod would be a bit to hard to do.

But, I think the speakers would be easy (somewhat).

A few questions:
1. What is the part number on the amplifier chip in your speakers?
2. What type of power supply is it running off of? A lightweight switching supply, or a heavy, iron core transformer based one?

[Mrx3750]

Re: A couple questions about some ideas I have

Ah, the walkie talkie i don't care much about. The speakers however, lets see here.

Power supply is a small transformer. The amplifier is I'm guessing this 8 pin IC here. Part # UTC2822M

[mariushm]

Re: A couple questions about some ideas I have

can you post some pictures of the speakers and the board inside ?


UTC2822M is probably a clone of TDA2822M.

Here's the datasheet

UTC2822M made by some chinese company:

And the TDA2822M made by ST / SGS-thomson :

Both the chinese and original chip say they support absolute maximum of 15 volts, but the chinese one says maximum under regular use of 9v , while the tda2822m one says 12v.

You could measure the output of that transformer to see what's the input voltage... I would guess it's 4.5-6 volts. If so, you could probably replace the transformer with a larger 9v ac transformer and a bridge rectifier and a capacitor that will give you about 10-11v DC.

Either way, it's a lousy, cheap amplifier... with 8 ohm speakers and 6v input, you get about 1.3 watts of power with 10% thd according to datasheet, which is crap.

There's another graph in the tda2822m datasheet :



So basically with 8 ohm speakers once you go over 9v, distortions are higher than 1% (which is the maximum i'd tolerate) and you only have 1w of audio power.

If the transformer is really small, just enough to give the amp let's say 4.5-6v @ 1A (so around 10va) or something like that , then raising that capacitor after the bridge rectifier to a larger value might make the amp get more input voltage (with less ripple) during operation and that may give you a bit more volume before it distorts too much.
But I still say it's just a crappy amplifier.

[lti]

Re: A couple questions about some ideas I have

There is nothing you can do about the noise on the output. That is just the fault of the crappy amplifier chip. It is known for that.

[Mrx3750]

Re: A couple questions about some ideas I have

Oh. So no way to reduce the noise on the headphone output?

[ben7]

Re: A couple questions about some ideas I have

Oh. So no way to reduce the noise on the headphone output?

The only way to do that is to use a different amplifier chip with better noise performance.

[Mrx3750]

Re: A couple questions about some ideas I have

Oh well. It'll be easier to hunt down a better pair of speakers.