need tda7240 guitar amp schematic

[jogina111]

yeah, Im still looking for a psu...so far, 800mA is the highes I can find...

[Jdansti]

BTW- There is another option if you can find an AC to AC wall adapter that has 12-35VAC out and is rated at 2A or more. With a few diodes and capacitors, we can easily get you fixed up with the DC power you need.  You'd need to put the extra components on a separate small board. It'd be a good learning experience about power supplies too.

[jogina111]

maybe I could... I need to earn some money first so I could buy a bare transformer. I already got one here but its a 9 volt transformer..

[Jdansti]

maybe I could... I need to earn some money first so I could buy a bare transformer. I already got one here but its a 9 volt transformer..

Or scavenge one from an old radio or something. Just be careful of the capacitors when you're cannibalizing. They can hold a charge for a long time after they were last powered up.

The reason I mentioned an AC to AC wall adapter is that you won't have to get near the mains power. You could build a plug-in power supply from the ground up, but you better know what you're doing to keep things safe!

[jogina111]

oh! I found one it says:
HT 4098
2A/28VDC
1A/220VAC
COIL:12VDC
Could it be that this is a dc to ac transformer? And I dont even know which poles should go to the mains...

[Jdansti]

The "mains" refers to the voltage at the wall plugs in your country. I understand that you have 220VAC or 230VAC at 60HZ there in the Philippines.

The adapter you found takes 220VAC from the wall and puts out 12VDC (I think).  I'm a little confused by the specs showing two different DC outputs, but only one AC input. Do you have a URL that you could post so I could look at it?

[jogina111]

you mean a picture? I'll try to upload it tomorrow...

[Jdansti]

you mean a picture? I'll try to upload it tomorrow...

I was hoping to get a URL (web address) for the item and look at a data sheet.  I searched for HT 4098 and couldn't find anything.

I guess that you're looking at a model at a store. If you could get a photo of the specs on the package, insert sheet, or the unit, that might work. The more detailed, the better.  The manufacturer's name would help too.

[jogina111]

oh..i just found it..Not at a store. Its just a scrap.

[jogina111]

maybe a transformer from cfl's will do, since a cfl can deliver 18 to 23 watts?

[Jdansti]

I don't think so. Too small.

I=P/V

I=23W/220V

I=0.1A  or 100mA

Nice try.

[Jdansti]

Actually, I may be wrong in my last post. If we assume that the secondary is 12V (I have no idea what it really is), then it might handle close to 2A.

I'm just not able to intelligently help you with the CFl transformer idea given that I don't have the actual specs of the transformer in the CFl.  I'm not going to guess due to the danger of being wrong and getting someone hurt or burning your home down!  Maybe someone else knows.

[PRR]

Compact Fluorescent Lamps do not have anything like a conventional transformer.

I'm real nervous about *any* line-power work by an electrical novice. A mistake on a signal jack gives bad/no sound. A mistake in wall-wiring burns the house down, or stops your heart.

What about a car battery charger? 12V 2 Ampere is a common car-batt charger, is isolated, is polarity-marked. Car-batts do not need filtering, audio does, so you hang a 3,300 uFd 25V capacitor on the "12V DC" output and get around 16V DC no-load.

[Jdansti]

Great idea Paul!

[jogina111]

Okay! I got one! 12volts, 2.1 Amp wallwart... I just hope its not noisy..

[Jdansti]

Good news!  We can do things about noise. Is the output 12VAC or 12VDC?

[jogina111]

it says ac-dc adaptor/charger input:220v-60Hz 
output:12v 2.1Ah

[Jdansti]

Are there any symbols next to output labeling such as

______
----------      or       ~

[jogina111]

yes the--- under ____ is between 12v and 2.1A
and its 220v~60Hz..

[Jdansti]

Good, that's 12VDC. So now we just need to decide whether you keep the LM338T voltage regulator in the circuit or just use the raw 12V from the power supply. If you use the regulator, the circuit will have around 10V at the regulator output, which will reduce the amp's output volume.  I like Paul's suggestion of leaving it out.