Building an amplifier power supply using a voltage doubler and LM317?

[hornloaded]

I was considering purchasing a kit such as: QKits Electronic Kits: FK656, Power Amplifier Kit OTL 30W (Mono) R1%

To use as the output stage for an amplifier. I just won an ebay auction for a 40VA 24CT transformer. Now obviously the voltage output of the transformer would not be high enough for that kit. So I was thinking about building a voltage doubler circuit. And then after the circuit, I would use a LM317 for regulation.

Would this be a bad idea to regulate the p/s? The max output current of the LM317 is only 1.5Amps, so it would be cutting it pretty close. I wouldnt need the full 30 watt output of the kit, even 20 watts would be fine.

It would be driving a single 8ohm guitar speaker.

 

[hornloaded]

Has anyone used a Voltage doubler circuit before?

 

[Nelson Pass]

It takes a lot of capacitance and probably more transformer
to build a voltage doubler good enough for the power stage
of an amplifier. Normally this technique is reserved for low
current use, as in creating higher rails for front end circuits.

 

[hornloaded]

Ah, that makes sense. Even if you used a full wave bridge rectifier in the doubler section, would it be a lot less efficient than a standard power supply?

 

[h_a]

if you used a full wave bridge rectifier in the doubler section

That's not possible, because that's the essential part how the voltage doubler works.

Have fun, Hannes

 

[bobodioulasso]

You need a 2x20v transformer .

 

[hornloaded]

That's not possible, because that's the essential part how the voltage doubler works.

Have fun, Hannes

What about this example:

File:Full-wave voltage doubler.svg - Wikipedia, the free encyclopedia

 

[Greg Erskine]

That's just normally regarded as a full-wave bridge rectifiier in my books, but I can see why it is called a voltage doubler. Do you need +ve and -ve rails? YES

The simplest solution, is just buy the right transformer.

 

[kevinkr]

Check out Antek toroids - I am sure they make something suitable for your application at a price that will surprise you. (I've been using them for years.)

Antek - Your reliable source of transformers, power supplies, and more. I think a 100VA transformer AN-1232 would be adequate for this application. See page here: http://www.antekinc.com/details.php?p=42

 

[bobodioulasso]

a 2x20v xformer will give aproximatively
20v x 1.4 = 28v DC
20v x 1.4 = 28v DC
2 x 28v DC is ok for a 30 w amp (8 ohm supposed ?)

I wouldnt need the full 30 watt output of the kit, even 20 watts would be fine.

 

[CBS240]

full wave voltage doubler....


It appears the kit requires a +/- supply. You can build a regulated +/- supply with 2) LM317's, but you must have two seperate secondaries, not a CT. Otherwise you would need the - reg, LM337. You will loose a few volts with forward diode voltage and ripple and you would need to have much larger caps. It really would be easier and probably cheaper in the end to find a proper transfo.

Besides, your transfo is undersized by over half that's required.

It's too bad you didn't win two of them.

 

[hornloaded]

Sorry for the necrobump, but what about this one:

QKits Electronic Kits: FK658, 35W Mono Power Amplifier Kit

It says supply voltage of 35vdc, it doesnt mention any +/- rails.

24vac * 1.41 = 33.84 vdc, slightly lower than the 35vdc requirements, but would this work with the 12 - 0 - 12 transformer?

 

[bobodioulasso]

It seems to be half of FK659 kit which requires +35v/ 0/-35v. If so, same problem.
Anyway, a single 35v supply cannot produce 35w/8ohms.
With your transformer you could feed a lm3886 kit for 15watts output.

 

[hornloaded]

Hmm, the gainclone kit would probably work well, I could just buy the PCB's, and then reduced voltage components since I wont be running it full bore.

 

[bobodioulasso]

Lm 1875 kit also with the possibility to bridge the outputs to obtain more power.
http://www.chipamp.com/
http://cgi.ebay.fr/ws/eBayISAPI.dll?ViewItem&item=260425122111

 

[hornloaded]

how hard would it be to bridge the outputs on that kit for the ebay auction? It will be used for powering a guitar speaker, so I don't need stereo.

Looks like the 2x12v transformer is just barely enough, but it should do!

 

[bobodioulasso]

See the datasheet and the following thread.
(This is possible if the speaker is not less than 8 ohms.)

LM1875 - 20-W Audio Power Amplifier
http://www.diyaudio.com/forums/chip-amps/115239-lm1875-bridge-config.html

 

[hornloaded]

Well I bought that kit on ebay, thank you for the link. Now hopefully I can figure out how to bridge it! Although I probably won't even need the full power output of one channel.

 

[AndrewT]

build one channel on a proto board.
Test it with your 12+12Vac supply and then listen to it.
After that decide what comes next, just not now!

Use 50V smoothing and decoupling capacitors. This allows for 28+28Vac transformer later if you want to go that way.

 

[hornloaded]

So what enclosure would you all recommend to use with this kit? I have everything else that I need I think.

I looked at a Hammond Die-cast aluminum enclosure, but it was 35 dollars, more than the cost of the rest of the components!

I was hoping to find something in the 10-15 dollar range.