Dual rail from trafo with no CT?????

[madtecchy]

John
I like crazy lol my friends say even if they could change it they wouldnt.
Im liking the idea of recycled smps to run F5 i wonder what nelson would say ?
No big caps no big trafo,s regulated what more could we ask for ? nearly forgot the space requirments that leaves more room for bigger heatsinks.

 

[john65b]

I would try it without the smoothing caps....would they even be needed? Like you said, regulated and able to deliver a nice steady current.

As a sanity check, the load on these laptop supplies on an operating laptop was twice what it was on my Zen V5 biased as I described.

 

[madtecchy]

Only thing is is when you hit the limmit with a smps its over. i guess as long as the smps's can deliver at least the peak instant current demand then all would be good.

 

[hotiron]

OOPS!

LOL I didn't realise you were talking about powering class A amps.

 

[madtecchy]

Let it flow LOL

 

[redsky]

Hi All,

I try to using this schematic from QLS PCM1793 Audio DAC Power Supply . But I changed the chip with TDA2050.

An externally hosted image should be here but it was not working when we last tested it.

Using this to supply my CMoy pre-amp for low voltage supply.

But I want to know if schematic can be using for higher voltage (about +/- 15 Volt DC output) to drive my amp ?

Regards

 

[redsky]

Sorry, just to make sure you can see the image.

An externally hosted image should be here but it was not working when we last tested it.

 

[KatieandDad]

It'll do +/- 15V but only at the maximum output current of the op-amp.

 

[KatieandDad]

I'm going to be screamed at for this I know.

ONLY attempt this with great care.

With a toroidal transformer the windings are fairly easy to access. It's not uncommon for the secondaries to be on the outside of the toroid.

You can, WITH GREAT CARE, scrape a tiny amount of the varnish off the winding and make your own centre tap.

If you break into the Primary then you will have to ensure that you apply a drop of transformer varnish in order to re-establish the insulation.

This is ONLY suggested to someone with a modicom of knowledge about electrical safety and MUST NOT be attempted by a novice.

 

[bear]

Hi All,

I try to using this schematic from QLS PCM1793 Audio DAC Power Supply . But I changed the chip with TDA2050.

An externally hosted image should be here but it was not working when we last tested it.

Using this to supply my CMoy pre-amp for low voltage supply.

But I want to know if schematic can be using for higher voltage (about +/- 15 Volt DC output) to drive my amp ?

Regards

Amp?

Power amp?

Not likely. It will not produce enough current.
Higher voltage, sure.
Can't exceed the voltage or current rating of the opamp no matter what.

But you have to watch the voltage being dropped by the 3 pin regulators, more drop compared to the unregulated rails = run way hotter.

This is not a great way to make a power supply, except in a pinch or where you want to save money.

_-_-bear

 

[redsky]

Thanks KatieandDad.

Actually I'm a Novice. And another problem, in my hometown is very difficult to find a good part for audio in local store . Etc, to find a good transformer. So in my projects, I try to using many part from my old branded equipment.


In TDA2050 datasheet, I found : IO Output Peak Current (internally limited) 5 A. Can you help me to explain how much the output voltage can be produce with that op-amp ?

If I using +30 volt DC from external single suply PSU as source, can I use that schematic to produce +/- 15 DC ?

Regards

 

[KatieandDad]

The CMoy on its own will probably work with just a simple potential divider and two reasonable caps.

Anything more and look at all the posts above that say NO, NO, NO.

 

[KatieandDad]

I dont think that the TDA2050 is intended to be used in this fashion.

Others may be more aware of its unusual properties.

 

[KatieandDad]

Going back to Post #1.

What sort of current are you after ?

What is the rating of the transformer ?

 

[AndrewT]

Post27.
The 12V 1A supply must be 12Vac and the secondary winding must be isolated from all other connections.

The virtual ground formed by the opamp will force the 12Vac to become a non centre tapped 6Vac & 6Vac centred around the virtual ground.

Now you have an effective 6Vac feeding the rectifier and thence into the 5Vdc regulator. You may need to use an LDO regulator due to low overhead across the regulator.

Could someone check my logic???????

BTW,
the LED will be dim, if only 1mA is passing.
If it's only 0.5mA, then even dimmer.

 

[redsky]

Going back to Post #1.

What sort of current are you after ?

What is the rating of the transformer ?

To drive my amp, I think about 1.5 Amp max.

 

[AndrewT]

If you want 1Adc, then the transformer must be rated >1.5Aac and preferably ~2Aac.

 

[KatieandDad]

1.5A you are on a losing streak.

You will need another transformer.

30VA transformers are not expensive.

9-0-9V at 1.5A = 30VA will give you unregulated 12-0-12VDC.

If you want regulated supplies then you will need 12-0-12V at 1.5A = 40VA (50VA to be practical).

You can get them for about £20 GBP

http://www.amazon.co.uk/CAMDEN-CTFC...VK/ref=sr_1_13?ie=UTF8&qid=1336654102&sr=8-13

http://www.amazon.co.uk/Multicomp-M...VW/ref=sr_1_22?ie=UTF8&qid=1336654155&sr=8-22

http://www.amazon.co.uk/Camden-CTFC...BQ/ref=sr_1_23?ie=UTF8&qid=1336654204&sr=8-23

I could go on forever.

 

[bear]

Indonesia, iirc has a pretty big electronics manufacturing industry.

You might look on the local ebay or the equivalent sites...

transformers from things like discarded UPS supplies for computers are good sources for iron... older broken receivers and the like...

_-_-bear

 

[redsky]

Hi Guys,

You're right. I can make an order from eBay. And I did it. But for Nubie like me, I just curious to understanding about the theory. Today I was follow the schematic to drive my cMoy preamp. And its work as well. Just replace LM1875 to TDA2050.

So, I think if it can produce low voltage, why it is cannot be use for higher voltage ? Sorry for stupid question...

Regards