If I wanted to build my own power supply

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If I wanted to build my own power supply

Post by rwc » Thu Apr 16, 2009 8:42 pm

I'd like to make a unit consisting of a kickass A/D, D/A, and mic preamp.

I need +/- 15v around 1 amp, +12v around 1 amp, +5v around 1 amp(if not less), and +48v around an amp.

I could just buy a bunch of power one linears. But, I feel like after over 2 years of repairing screwed power supplies and messing with gear that it's time to take the next step and build one.

Would it be more sensible to make my own than to buy separate ones for each of those voltages?
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Post by lacquer_monkey » Thu Apr 16, 2009 10:36 pm

What, exactly, do you need an effing amp of 48v for?
uh... what??

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Post by drunton » Fri Apr 17, 2009 12:05 am

Build it yourself, but use these kits: http://www.jlmaudio.com/JLM%20Power%20Supply.htm

You'd have to heatsink the crap out of it, but the LM317's are rated for 1.5 amps, though the 48V probably won't provide that much current with the voltage doubler.
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Post by rwc » Fri Apr 17, 2009 8:11 am

lacquer_monkey wrote:What, exactly, do you need an effing amp of 48v for?
Some old gefells work like shit off of(gasp) some neve console mic pre modules unless you use an external phantom supply. I don't want to worry about it. If I'm building from scratch, might as well do it right! Right now this is just going to power a dual channel mic pre, but for cost savings, would probably get used for over 16 channels eventually.
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Post by nclayton » Fri Apr 17, 2009 10:38 am

I'd say it would be sensible to make your own. They're easy to make.

I think the JLM supplies are nice for convenience if you don't need much current and don't feel like making your own circuit board, but I don't think they have a version that's easily adaptable for 4 positive voltages including the 5 volt and phantom. I might be wrong about that.

Since you want to be able to supply an amp of current you're going to have to screw your regulators to a chunk of aluminum. You can also buy bridge rectifiers that easily screw down to your chassis. If I were you, I'd just build your supply without a PCB. Attach the regulators and rectifiers to the chassis and use tag strips or cap clamps to hold the capacitors. Just be sure that when you solder to your regulator pins you use heat shrink to keep them from touching one another.

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Post by rwc » Fri Apr 17, 2009 10:31 pm

I don't mind not having a PCB. I have 100' of heatshrink perfect for IC pins.

the reason for the +/-15v, 5v, 12v, and 48v was so I can have one unit that can power my modded D/A, eval board A/D, and mic preamp, so I can have two pristine world class portable channels of in and out for under $600 that can travel anywhere and work with everything from the mbox to protools HD.

what exactly am I looking at in terms of building it? I understand how a power supply works, and I sometimes know what to look for in repairing them, but I've yet to put one together so I can't drum up a parts list in my head. this would be a great time to start, but a PSU with this many outputs seems like it'd be tricky.

I'm guessing:

a transformer to step down the big AC from the wall to small AC

a bridge rectifier to separate the AC into + and -

capacitors to smooth the new DC down so it doesn't look like a cut-off-in-the-middle sine wave

voltage regulators to make it precisely the voltage I need.

the only thing that i find tricky is, how the values work so I get a specific voltage.is that a function of the transformer I use, or a function of the voltage regulators, or both?
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PSU build

Post by Time Tech » Fri Apr 17, 2009 10:58 pm

You are probably looking at building 3 supplies. One for the bipolar(+/- 15 to 18vdc adjustable) one for the +48vdc and a third to create the 12vdc and 5vdc.

There is some linear PSU voodoo about using separate rectifier diodes to make a full wave bridges for audio supplies. A FWB package for the 12 and 5 volt supply should be fine.

The supply components can be mounted to project perf boards to ease the layout.

All the supplies can live inside one enclosure, and as mentioned before the voltage regulators can be screwed to the case to act as a heat sink. In addition to shrink tubing the regulator legs, use mica or silicone isolators and thermal transfer grease to improve the heat transfer to the case. The real tricky bit is securing the device to the case with out having the mounting hardware short the mounting tab of the device to the case.

Always allow as much "over-rating" to the part tolerance as size and cost allows. Running parts close to the edge of thier ratings will work for a while, but will probably shorten the overall lifespan of the project.

Linear supplies are pretty straight forward to build. If you have any surplus electronics shops in your area you should be able to get everything you need. If not, a good surplus place that I use is All Electronics in Van Nuys Southern California. They do internet sales as well.

Have fun with it and don't forget the fuse.

Cheers,

Bruce Maddocks
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Post by rwc » Sat Apr 18, 2009 6:31 am

Ok, imagine I'm retarded.

When you say 3 PSUs - do you mean 3 transformers, 3 full wave rectifiers, and 3 sets of smoothing capacitors before each voltage regulator?

Or 1 transformer, to 3 different full wave rectifiers, to 3 separate sets of smoothing capacitors, before each voltage regulator?

I have never done this from scratch.

Thanks!
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short bus psu design

Post by Time Tech » Sat Apr 18, 2009 10:30 am

3 transformers;

1 center tapped secodary 12vac for the bipolar
1 12vac secondary for both the 12vdc and 5vdc supply
1 36vac secondary for the 48vdc

3 FWB

2 smoothing caps before the regulators(aside from any needed caps to compensate for regulator distance from the load) I use a smaller mF cap as the first filter, place a resistor in line to feed the next larger value mF cap.

A large smoothing cap fed from directly from the fwb may appear as a "short" to the transformer when it is switched on.

You should use adjustable regulators for the bipolar, 12vdc and 5vdc supplies.

You may have to use a large case transistor (2n3055) as a pass transistor regulator to get your 48vdc.

All the separate transformers should have thier own fuses, and for added fun and amusement you may want to consider indicator lights(LEDS) to display that each voltage is working, and a fuse on the output of each supply.

Cheers!

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Post by The Scum » Sat Apr 18, 2009 5:13 pm

Go track down the datashets for the candidate regulators, and start by reading them. 78xx/79xx (replace xx with the desired voltage), and LM317 are good starting points, and they provide some reference designs that will be a good starting point.

Keep in mind that the 78/79 regs don't have the same pinout, and the taps can not be in electrical contact with each other (or bridged by the heatsink).

If this were a commercial product, it'd use a single transformer with a whole slew of secondary windings...one for each rail. But if you can't get something custom wound, you're probably looking at a separate transformer for each supply, with following filter caps, rectifiers, regulators and reservoir caps.
Ok, imagine I'm retarded.
Then I'd be wary of letting you do the mains wiring this will entail. :wink:
I have never done this from scratch.
And even though I'm qualified, I only rarely get to do it. Why? Because for my labor, Power One builds a much better supply than I can. Good power supplies are just as specialized a discipline as any other branch of electronics.

I can lash a few 78xx/79xx/317s together, and have a functional supply. 78/79's are the regulator equivalent of a 741...noisy, obsolescent crap (but still OK for 80% of what most folks need...rectifier, 2 caps and a regulator...voila, instant supply).

The 317 is better, but still long in the tooth...and it takes a few more parts to get there than the 78/79.

By the time you get any DIY supply stable while delivering 1 amp on each of 5 rails, you will have earned more than a few hard-knocks experience points.

The Power One supplies use newer, better regulators...and they take more parts to put togethet...but give you features as welll...over current, over temperature protection, load-sensing regulation, lower noise, optional crowbar protection, and the knowledge that they will defnitely provide the current they're spec'd for. Plus pass transistors and heatsinks built right into the units themselves, built by folks who know how to get reasonable utility from those features. By the time you've got 3 or 4 transformers, you're not far away from the size or weight of a handful of Power One modules.
Some old gefells work like shit off of(gasp) some neve console mic pre modules unless you use an external phantom supply. I don't want to worry about it. If I'm building from scratch, might as well do it right! Right now this is just going to power a dual channel mic pre, but for cost savings, would probably get used for over 16 channels eventually.
I still question this...Phantom is specified as 48-ish volts across a pair of 6.8K resistors...leaving ~14 mA available for each mic, into a dead short. Having 1A from the supply, it's still coming across those 6.8Ks. Even across 16 channels of dead short, that's about .25A.

Most vintage Neve pres had no actual provision for phantom - it was cobbled in elsewhere...6.8K resistors in a patch panel or similar. Is there a chance that the power in your anecdotal evidence could have been misapplied?

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Post by rwc » Sat Apr 18, 2009 10:29 pm

I like power one. But that'd require buying a 15/5v, a 12v, and a 48v. acopian did the same thing, and linked me to 3 separate power supplies that were both way more expensive than the power ones.

I wasn't doing this to save money off buying a $300-$600 supply, but rather because it seemed more practical. I don't need gobs of power output from this since for the beginning it'd be powering a dual channel A/D and mic preamp and that's it.

I'd much rather buy one from someone qualified for this than mess with it myself, but I can't find anything remotely like what I want anywhere. I want something that'll work with most digital circuits(5v), phantom power(48v), most audio ICs/transistors/ADCs(15v) and what will work with my modified DAC(12v)
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Post by Galen Ulrich Elfert » Sun Apr 19, 2009 11:38 am

Before you get in too deep, you might want to have a look at these:

http://electronics.dantimax.dk/Kits/Pow ... index.html

They're kits, so you still get to learn how it's all put together, but with less risk of catastrophic failure. And the price is hard to beat.

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Post by Galen Ulrich Elfert » Sun Apr 19, 2009 11:43 am

The 48V is only 100mA, but seriously, if your mic is consuming 50W, I would think there's something wrong with it. I don't know about those phantom powered tube mics though.

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48 vdc supply

Post by Time Tech » Sun Apr 19, 2009 1:12 pm

The Scum is correct on the 48vdc current draw needs for Phantom Power.

1 amp out would be "overkill".

I am not in total agreement with using the fixed voltage 78xx/79xx regulators. My experience has been that the positive output ones come up just allitle short of thier advertised voltage value.

The fixed regulator designs do have a smaller parts count, but IMHO having the ablity to "fine tune" the output to a dead on value is a added value, especially if the supply is located some distance away from the electronics it is powering. You would measure the voltage at the power input pins of the device and adjust the power supply output to the correct value for that device. That would compensate for any resistive loses in the power cabeling.

The more matched the Bipolar (+/-) voltages are at the device the possiblility of a "DC offset voltage" on the output of the device is reduced.

Still Have fun with it.

Cheers!

Bruce

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Post by Scodiddly » Sun Apr 19, 2009 2:07 pm

Damn ... somewhere around here I had a schematic for getting a 48vdc supply from the same 15vac transformer used for the +-15vdc supply. It did a sort of voltage doubler/tripler thing on the AC side to get a high enough voltage. Basically just diodes and capacitors, pretty easy to build.

I was last working on that project about 4 years ago. :oops:

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