[divie23]

I'm sure this one has been done to death but a search didnt prove helpful due to the vast number of different PS's out there.

I'm looking to build a simple, mains, IEC type input, supply to power my buffered CMOY. I only require a single supply since I am using a buffer in a seperate enclosure, together with the amp, to provide + and -.

I would really appreciate direction to appropriate schematics.

I'm intending to use a toroidal trans also.

Is there really any need for a lm317 regulator since minor fluctuations in volatage won't matter as long as both OPAMPS receive the same voltage? Simply using huge mama caps will still provide linear supply, no????

If there are added benefits then making a lm317 regulated supply is no problem - in fact its more fun!

Cheers!
divie

 

[divie23]

One more thing!
What rated transformer should I use. I was thinking 50VA should be sufficient and a 25V rating would give me about 35V (25x1.4). 35/2 = 17.5V approx for each opamp and each output buffer. sounds good right?

 

[guzzler]

here's mine:

http://www4.head-fi.org/forums/showt...ighlight=power

50VA is far too much, look at more like 15VA with 15 or 12V secondaries for an output of 24V

g

 

[divie23]

thank you guzzler, you've saved me a shedload of work!
nice **** on that page too

 

[divie23]

ok let me get this right -
i've come across a 2x15V Secondaries. That gives 30V when done in series, that gives single output of +42V (30x1.4) after rectifier bridge.

This 2x15V is rated at 0.5A. Is that sufficient?

Thanks again.

 

[divie23]

if i have 42V what should i set the regulator to output. Will Vout have to be less than Vin ?

 

[Voodoochile]

It's overkill, but should be fine. What are you regulating down to?

If you dissipate more than about 5 or 6 volts, you will want a heatsink on that 317. But it does not have to be a monster, either.

Yes, output must be at least 3.5v below the input. 5v is ideal, IMO.

Your BB OPAs are typically +/- 17v max (34v) and some AD chips are lower, at +/-13v (26v). So, be careful how high you go! If you are using a 2132/34, I'd reg it down to 30 or 32 volts. Watch out for your caps, too. before the reg, they will have to be 50 volt capacity.

 

[guzzler]

you could happily use 12V secondaries... as for current, i doubt your CMoy buffered and all will draw much more than 30mA!

edit2: i set my output from the regulator to 24V, i think anything much above that is just gonna dissipate too much heat for no material gain, although at 24V the regulator is dissipating a very lot of heat if your secondaries are 15V

g

edit: grammar dammit!

 

[divie23]

Ahh beginning to make sense. 2x12V will give +33 and just use 317 to regulate it to 24V. Nine volts to rid of, so a heatsink looks likely.

am using opa637s together with el2001s. so +/- 12V should be just fine

 

[Voodoochile]

True, but if your chip will take 32v, reg it down to 28v and call it a day. If you are using an AD8620, then 24v is a better idea for sure.

Edit: One last thing. If you are choosing a toroidal transformer, they put out a slightly higher voltage when relatively unloaded (this is your situation for sure with that transformer!). Search TE62022-ND at Digikey. Then select the manufacturer's data sheet link. It shows all the specs you might find interesting.

I'm not suggesting that tranny, but rather provide that as a convenient way to link to something similar.

 

[divie23]

Makes a great deal of sense. What's so magic about 12 anyways!
I'll check the spec for the amps and do the rest. otherwise, i'll try to find a lower current rated tranny. see what u mean about overkill lol

cheers guys

 

[Voodoochile]

I just see that you are using the 637s...

I love them.
I'd feed those babies +/-15 or +/-16v if you can swing it. Build the PS, measure the raw output before the reg, and then pick your adjust resistors to net you 4 or 5 volts less, assuming you are ending up below 33v regulated.

Lastly- if you are building this amp with those OPAs and the EL buffers (pretty nice place to start), and you are going to build a seperate PSU (also nice), why not go ahead and build a regular dual supply? Just a thought... you are going 90% of the way already, as the single PSU has the tranny, bridge diodes, board already. A few more caps and another reg and you are there. It will be very nice either way, and I do not intend to discourage you from going the route you are going.

I have no further comments, other than be sure to post a pic of your handiwork when it's finished.

 

[divie23]

good point voodoo. a dual supply certainly would rid the bug to upgrade again! the only thing is i've had my amp built for over a year now and have been using a crappy wall regulated DC supply.

I'm using a BUF634 splitter (preceded by resistor divider) within the amp enclosure itself to split and form the dual supply. SO really I only need a single supply since the BUF will do the rest.

You have got me thinking though, since I could quite easily modify the existing amp. It would mean a new power input connector,as opposed to the 2.5mm DC socket I'm using now, since I'd need another terminal to connect earth from the PS and the BUF circuit in the amp. I'm sure the resistor divider before the BUF would not do any damage. One thing though is it safe to feed the BUF dual voltage? Also, am i right in thinking that I would simply feed the +/- from the PS directly to the resistor divider?

It'll be a lot more work but it's certainly possible. Would it be worth all the extra hassle though?

 

[divie23]

hopefully that last post makes sense. But from the looks of it I'm in the same boat as guzzler and his META. He already has a voltage splitter on board the META PCB so only needed a single supply.

But I'd be keen to know the benefits of a fully blown dual regulated supply, voodoo?

 

[guzzler]

a dual supply should provide better isolation between the rails so a large positive load shouldn't affect the negative side un-duly...

if you do go with a dual, you'll have to remove the resistor splitter and BUF...

g