OK, I'm really trying to build on a budget for a simple LM1875 pc amp, and I have a pair of Netgear router wallwarts that on the back have this info:
I\P: ac120v 60hz 22w
O\P: AC16v 1000ma
So what do you think? With the right rectifier, could a wallwart run a 1875? I know it would be a little underpowered, but since its for a PC speaker (Gonna build the Elf 1.0) It would be perfect to run a pair of wallwarts for a pair of 1875s
I\P: ac120v 60hz 22w
O\P: AC16v 1000ma
So what do you think? With the right rectifier, could a wallwart run a 1875? I know it would be a little underpowered, but since its for a PC speaker (Gonna build the Elf 1.0) It would be perfect to run a pair of wallwarts for a pair of 1875s
It should work. You could use a single supply and output cap, or you could create a virtual ground and run it from split rails. I have done this successfully with a steady 500mA load; at 1000mA of dynamic load, YMMV. Maybe someone else will comment or go single-supply if you want a sure thing.
You will only get about 4W into 8 ohms.
You will only get about 4W into 8 ohms.
Jcoffey
You don't need to do single supply or output cap. Have a look at
http://sound.westhost.com/project05.htm
You should do something along those lines.
This project if for pre-amps, but with your tranformaer size, it should work fine.
You don't need the regulators unless you capacitors are very small..............on the other hand with your small transformer it should also work fine with them included.
Your 16 V AC should give you something like +/- 20 V DC witch should be fine for your LM1875 and your PC-speaker.
Regards
Thomas
You don't need to do single supply or output cap. Have a look at
http://sound.westhost.com/project05.htm
You should do something along those lines.
This project if for pre-amps, but with your tranformaer size, it should work fine.
You don't need the regulators unless you capacitors are very small..............on the other hand with your small transformer it should also work fine with them included.
Your 16 V AC should give you something like +/- 20 V DC witch should be fine for your LM1875 and your PC-speaker.
Regards
Thomas
there is a schematic for single ended operation of the LM1875/3875 on Nat Semi's web site -- after all, it is an op-amp
tlmadsen said:
Just so I understand you correctly, by using one of these boards, with the wall wart connected to it, gorund to the chassis and run the outputs to the 1875. If it's that easy, then sweet! but will it really only put out 4 watts?
The power supply shown in project 5 uses half-wave rectification since the transformer has only a single output rather than two or a centre-tapped output. You can certainly do the same thing for your amplifier, but omit the voltage regulators. Basically, you just need everything up to the first pair of 100nF caps. You might want to increase the filter caps to more than 4700 uF though - since this is half-wave recitified, the caps only charge half as often, so they'll need to store twice the energy as the caps in a full-wave rectified design. I'd start with 10000 uF and see how that works.
Or, instead of using one walwart and a half-wave rectified supply per channel, you could use both walwarts together to make a full-wave rectified supply. This should save you a few bucks on filter caps. Treat the output of each walwart as one output of a dual-secondary transformer.
Or, instead of using one walwart and a half-wave rectified supply per channel, you could use both walwarts together to make a full-wave rectified supply. This should save you a few bucks on filter caps. Treat the output of each walwart as one output of a dual-secondary transformer.
hehe ttt means To the top, if a thread is getting stagnant and you need peopel to read it you type that to bring it back up.
I'm not quite sure I follow your idea with using both wall warts as one ps. If I am, I should just pretend that both wall warts are 1 toroid transfo and use a rectifier bridge as one normally would? If I do, what kind of DC Voltage should I be seeing?
I'm not quite sure I follow your idea with using both wall warts as one ps. If I am, I should just pretend that both wall warts are 1 toroid transfo and use a rectifier bridge as one normally would? If I do, what kind of DC Voltage should I be seeing?
By the way gents this is known as a FULL WAVE voltage doubler supply because a cap is being charged on both halves of the AC cycle, not just one. The top cap on the positive half and the bottom cap on the negitive half = full wave. The suggestion to use big caps is a good one. The power supply has the two main filter caps in series so doubling the value is a good idea.
Later BZ
Later BZ
No.
This would be a full wave supply if it were only one supply. But it is two supplies, and each is a half-wave rectified supply.
macboy said:
Two supplies 180 degrees out of phase with a common reference point. The output of this, from + to -, recieves a charging pulse from the transformer each 180 degrees of the AC cycle. That makes it full wave. Look it up. It's just in the way you look at it.
Later BZ
Hi!
With your transformer you get 16W of power right? (W=V*I)
That means that with an average efficency of 60% (I guess it's close to the one of LM1875) you get around 10W; If you use this transformer for 2 channels (stereo) you can get around 2x5W. Remember that it is plenty of power for a normal computer speaker! The only thing you should remember is that your amp shouldn't ask more than 1000mA of your transformer boiled 🙂
So check with an amperometer and tune the volume in order not to go over 1000mA (only some rare peaks over are allowable).
If you want simple & cheap operation I would suggest:
1) Rectify the AC current with an integrated rectifier rated at least 2A
2) Put in parallel to the output a big capacitor; this is very important in your case beacuse of the small transformer used (I guess 4700uF 25V is enough)
3) Don't use a voltage regulator: Your amp doesn't need it and you don't want to waste power within a voltage regulator, would you? 🙂
Enjoy.
With your transformer you get 16W of power right? (W=V*I)
That means that with an average efficency of 60% (I guess it's close to the one of LM1875) you get around 10W; If you use this transformer for 2 channels (stereo) you can get around 2x5W. Remember that it is plenty of power for a normal computer speaker! The only thing you should remember is that your amp shouldn't ask more than 1000mA of your transformer boiled 🙂
So check with an amperometer and tune the volume in order not to go over 1000mA (only some rare peaks over are allowable).
If you want simple & cheap operation I would suggest:
1) Rectify the AC current with an integrated rectifier rated at least 2A
2) Put in parallel to the output a big capacitor; this is very important in your case beacuse of the small transformer used (I guess 4700uF 25V is enough)
3) Don't use a voltage regulator: Your amp doesn't need it and you don't want to waste power within a voltage regulator, would you? 🙂
Enjoy.
- Status
- Not open for further replies.