[Folsom]

I am asking mostly because I have been having a HELL OF A TIME finding any kind of really nice regulator for 24v - but 24v + amplabs has one.

I thought about doing something like this (ignore the buffer, not using it)

http://www.diyaudio.com/forums/attachment.php?s=&postid=805978&stamp=1136397897

I was going to use quad FM capacitors for the 2.2mF and 100uf type N BGs after regulator or maybe FC/FM (depends how much the total for all this stuff is going to be), and for the bank of capacitors probably FM/FCs (on the right side of such schematic). Then some CREE diodes. Transformers I have found are all huge, at around 30v, but I will use one that size if I need too. (Parts Express).

That is my first idea. I am open to everything. I think 2a would be PLENTY safe and more than I need. Each buffer may only draw .5a but might as well have head room.

[dweekie]

What are you trying to power?  Also, if you get a kit, you can substitute the negative regulator (317 -> 337) and build up the rest of the parts in reverse (+ goes to gnd and gnd goes to + for all the caps, diodes reversed, etc).  It will mainly be a mental hurdle.

[dweekie]

Or you could get 2 regulator kits like the Tread for $17 each (http://www.tangentsoft.net/shop/details/treadkit.html) and hook them up for dual supply (http://www.tangentsoft.net/elec/tread/pguide.html#dual) with a proper transformer.

[randytsuch]

At the very least, I would use an adjustable three pin reg, LM317 or LT1038 type, and add a small (few uf) cap from the adjust pin to ground.  LM337 is the negative version of the 317.

In my squeezebox, to power my output buffers, I built "dual mono" regs.  I have one transformer, a split bobbin type, two full bridge rectifiers (8 diodes total), CRCRC smoothing caps, with panny FC's and a Jensen cap for the last C.  There are two sets of CRCRC's, positive and negative.  From there, I have four Teddyregs, a positive and negative regulator for each buffer.
http://www.pinkfishmedia.net/forum/showthread.php?t=39990
There was a group buy for teddyreg boards, but they are all sold.  But, as regulators go, it is pretty simple, and you can build it on perf board.

If you need more power, there is the powerreg,
http://www.pinkfishmedia.net/forum/showthread.php?t=39306&highlight=powerreg

I would think 4 teddy's would do just fine though.  I have a pretty big heatsink, recycled from a previous project, and it barely gets above room temp.

I would recommend starting was a simplier 317/337 regulator, and get it working with that.  Then, you might consider trying something more complicated, like the Teddy.

Good luck
Randy

[Folsom]

Well I have been hanging out at the DIY forum a little bit and came to this so far...

http://www.diyaudio.com/forums/showthread.php?s=&postid=1629474#post1629474

I have an extra PCB with 8 diodes laying around from a GC I might as well use.

A transformer I am a little lost on finding one that is under 160va and huge...

I only need maybe 1a per side. I think the Teddy is overkill.

[randytsuch]

If you want a torroid
http://www.antekinc.com/AN-0525.pdf

50VA, dual 25V secondaries.
25V will recitfy to 35VDC, unregulated.  50VA will give you 1 amp for each secondary, so you end up with 1A of neg 24VDC, and 1 amp of pos 24VDC, after your regulator.

Torroids are better for not generating a large magnetic field, but they have better high frequency response, which is a bad thing, in this case.  They will allow high frequency noise to couple into your circuit.

Otherwise, I would go with a split bobbin transformer.  Mouser and digikey carry hammond and other split bobbins.  I used mostly hammonds for my last project, but signal makes good transformers.

I don't agree that the Teddy is overkill, but I do agree that you are better of building a 317/337 based reg, for now.  Save the Teddy for when you have a little more build experience, although it's not that complicated.  Good, clean power is very important.  Depends on the PSRR of your design, but I always like a good, clean supply.

Randy

[Daryl]

Hi Smile Destroyer,

Parts express has buyout 25V, 2A transformers for under 3 bucks each.

Parts express also has the LM317 which you can find just about anywhere.

They don't have the LM337, you can easily find them elswhere but it's not necessary as you can build two simple +24V supplies in one cabinet and connect them together for an +/- 24V supply.

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=129-035

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=LM317T

Two 317's two transformers and two rectifier bridges along with filter caps, input caps, output caps and voltage setting resistors and your having a good time.

[Folsom]

I can just reverse the diodes to have the second do -24v correct?

At this rate I think I might go four transformers. I will have dual mono line amps. (why not I thought I was going to be spending way more money) This will also insure 1a worth to each line-amp.

Also I am going to use two extra diodes per 24v supply.

Parts list.

16 MUR860 Diodes (already have 8 ) (full bridge rectifying)
$1.16 x 8 = $9.28

4 Transformers (power in)
$2.88 x 4 = $11.52

4 LM317T
$2.25 x 4 = $9.00

4 120ohm Caddock MK123 resistors (needed in circuit)
$2.00 x 4 = $8.00

4 2.2kohm Caddock MK123 resistors (define value of 24v)
$2.00 x 4 = $8.00

4 10uf FC Panasonic capacitors (in circuit capacitors)
$.28 x 4 = $1.20

16 56uf FM Panasonic capacitors (output capacitors, four per output, should be super low impedence)
$.14 x 16 = $2.30

4 Panasonic X2 .01uf caps (for on each transformers, although I already got pretty sweet AC filtering)
$.91 x 4 = $3.64

1 Velleman ECS2 2 Hole Island Euro Card 3.9" x 6.3" ("bread board" but easier to deal with)
$8.76

Total = $58 for a pretty nice PSU, of course not nearly as nice as what it is going to drive but...

Anything else?

That makes my total for line-amp, with 4 JFETs $16, four Vishay resistors $7 a pop, $28, two RCA jack pairs $6.50 so $13.00, 4 feet jupiter copper $1.10 a foot $4.40, and two Sonicap platinum .01 teflon caps $18 a pop, $36

$97.41

$155 dollars for a only matched by other DIY buffers with slightly nicer stuff, no matter how much money you spend, and paid for by my good old pre-amp I had for phono! Sweet!

Thank you for your help everyone.

[Daryl]

Wow Smile Destroyer your on fire!

Don't reverse the diodes just build two simple independant +24V, LM317T regulated supplies.

Then to get +/- 24V you will connect the '-' of one supply to system ground and connect the '+' of the other supply to system ground.

The free '+' terminal will be the positive rail and the free '-' terminal will be the negative rail.

[Folsom]

Cool, I think dual mono is going to be best. Well on second thought, why.... I can probably do without.

Price difference $15 I think.

This is going to be sweet. Now if I can just figure out how to make my SB sound clean and have some good tonality, or do something. This should help a lot but I already know the detail is weak, and how smooth it is, it all falls behind.

[Daryl]

n

[Folsom]

I have no idea what N means Daryl but thanks again for your help.

Should my output caps feeding the JFETs be low or normal impedance? I was going to shoot for low but... someone else said I do not want that.

[Daryl]

I have no idea what N means Daryl but thanks again for your help.

It means I'm a (N)imrod (LOL).

I opened the thread to read your message and noticed mine said "The to get +/- 24V" instead of "Then to get +/-24V".

So I attempted to fix it with the 'Modify' function but clicked 'Quote' instead.

I proceeded to add my 'n' and noticed the modify screen looked wrong but went ahead and clicked 'Post' anyway.

When I saw the new message go up I knew then I am an idiot.

Then I tried to delete the message, I remember deleting messages before but now I can't remember how or else that option has been removed from the board software I don't know which.

Clearing the entire window and saving just gave an error that the message window was empty so I put and 'n' in and saved that.

[Folsom]

Oh ok. What are your thoughts on the impedance?  I ordered some caps but at .16$ I can order more ha.

[Daryl]

Oh ok. What are your thoughts on the impedance?  I ordered some caps but at .16$ I can order more ha.

By low or normal impedance do you mean large or small capacitors or something else?

I ask because you normally would categorize capacitors as low or normal impedance but certainly the larger a capacitor is the lower it's impedance over it's useful bandwidth.

Capacitors also are categorized as low ESR, high frequency and high temperature types (as well as several others) I want to make shure were on the same page.

And what was the reason given not to use a "low impedance" capacitor?

The more output capacitance the more you will shunt noise.

[Folsom]

I was going to use a bunch of FM panasonic ones which I think are low ESR and are 40 to 70% less impedance that the FC series (low ESR).
http://www.panasonic.com/industrial/components/pdf/ABA0000CE108.pdf

I am using 4 56uf FM's, in parallel on each output of the PSU ( the +/- 24v PSUs) to feed the lineamps (JFETs and Visahys with Teflon input caps at .01uf). Well that is the plan.

 

[Daryl]

They mean ESR is low for those capacitors.

I found some spice simulations on the net for 317's.

The consensus is that if the ESR of your output capacitors is too low you will have a resonance peak in output impedance due to the 317's inductive output impedance which causes a peak in noise and poor transient response.

That would be the reason someone else was recomending against low ESR capacitors as output capacitors (resistance in the capacitors damps the resonance).

Since you are using four capacitors in parallel as your output capacitor your ESR would be too low even if you used the regular capacitor type (their ESR is divided by four).

I would recomend for you to place 0.1 ohm resistors between the output pin on your 317 and the output capacitors.

This way your output capacitors are shunting the load and giving the maximum reduction in noise.

This topology will increase the ouput impedance of your regulator by 0.1 ohm but it sounds like the circuit you are building would be fine with that.

Also be shure to bypass the adj. pin also as it really helps performance with the 317.

 

[Folsom]

I am following this schematic.

http://cache.national.com/ds/LM/LM137.pdf

The ADJ runs in parallel to the output to create the 24v regulation, with 2.2kohm of resistance, and a 120ohm shunts the output to the parallel 2.2kohm.

I can through in some .1ohm resistors, I guess I will use some Caddock TF020 for the 2.2kohm and MP930 .1ohm and Caddock MK123 for the 120ohm.

[Daryl]

I am following this schematic.

http://cache.national.com/ds/LM/LM137.pdf

The ADJ runs in parallel to the output to create the 24v regulation, with 2.2kohm of resistance, and a 120ohm shunts the output to the parallel 2.2kohm.

I can through in some .1ohm resistors, I guess I will use some Caddock TF020 for the 2.2kohm and MP930 .1ohm and Caddock MK123 for the 120ohm.

Hi Smile Destroyer,

Don't use that schematic!

That's the data sheet for the LM337.

Actually everything is just inverted so as long as you were careful to invert everything the way it needs to be done for the opposite polarity regulator you would be fine.

I drew a schematic for you showing how to use two positive regulators for a +/- supply and including a series resistor for your multiple low ESR output capacitors.

The bypass for the adjust pin is also included here and it reduces noise by 20db or so.

The image is rather large because I made the writing too small in paint and if I reduced it any more you wouldn't be able to read it so you'll have to scroll it around to get a look at the whole thing.

[Folsom]

Wow, thanks Daryl.

The incoming .1uf capacitor I think has to be a 10uf capacitor according to the data sheet if an electrolytic is used.