[Build] Psuniversal

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Ptownkid

Well-known member
Joined
Feb 1, 2005
Messages
4,256
Location
Ajax, Ontario, Canada
I've been receiving many e-mails lately for tips and advice on building the Psuniversal so I figured I'd put together a build thread to address some of the questions. This PSU is capable of delivering 2 rails of positive voltages and one rail of negative voltage. One of the positive rails is set to +48V for phantom power via an 8K2 resistor by you could change this by simply switching out that resistor if you had the need for some other voltage. The other two rails are adjustable. The current capabilities are decided by the VA rating of the power transformer you choose and the regulators, which are good for delivering about 1.5A continuously but be aware that the use of heatsinks may be required if you are powering more than a handful of modules.

Kits available here

All the components on the pcb are labled, but some will be hidden once the parts are populated. Here are the relevant docs


Schematic


Overlay


As with any pcb, the order in which you stuff components should be based on size if at all possible. Start with the lowest profile parts first so that taller components do not make it more difficult to insert shorter ones later. In the case of this project, that will be the resistors and diodes. It is best if you use a lead bender. While not absolutely necessary, they make things neat and are very inexpensive. The resistors and diodes for this pcb are all 0.4" (10.16mm) spacing.

Bend diode leads to 0.4"


When inserting the diodes, pay close attention to which way the cathode faces. On the diodes it is represented by a thick band and on the pcb by a thick line. On this pcb they all face either left or up.

Insert all diodes


I like to avoid adding too many components at once so now is a good time to solder the leads and clip them. If you get too many components inserted at once, it makes it very difficult to maneuver your iron tip in to make good contact with the leads and pads. When soldering you should always try and touch the component lead AND the solder pad at the same time. Always touch the iron to the joint THEN touch the solder to the iron while still in contact with the joint. Not doing so can cause cold solder joints that will likely fail and are sometimes hard to find. A good solder joint should look similar to a volcano and be shiny.

Diodes soldered


You will need to sort the resistors by either using a multimeter or reading the colour code. It may take a while to memorize and get good at it, but learning the colour code is highly recommended. In this case, there's only two values so it's very easy.

Bend resistor leads to 0.4"


Insert all resistors and solder


Next up are the 0.1uF poly capacitors, there are only 4 and they have no polarity. If you are having any problems getting them to stay when you flip the pcb to solder, you can gently bend the leads away from each other to make them stay steady for you.

Insert all poly caps and solder


At this point I like to add C9-C11 and C13-C14 across the top of the pcb. These are electrolytic capacitors and as such they have a polarity. They are marked in several ways. The positive side is the longer lead, and the negative side is marked with a stripe down the side of the body. On the pcb itself, the positive is marked with a +. Attention needs to be paid to which way these parts are inserted. In the case of these five capacitors, the negatives all face to the right.

Insert C9-C11 and C13-C14 and solder


Now we come to the first of the larger electrolytic capacitors. At this point i only put C1 and C2 in so that I still have room to add the two voltage regulators and the trimpots. Alternatively you could simply add all four large caps after the voltage regulators and the trimmers. Again, pay attention to polarity. The negative face inwards towards each other.

Insert C1 and C2 and solder


Time for the voltage regulators. There are two different kind, so please be mindful of putting the right ones in the the right place. The top two are both LM317's and the bottom one is a LM337. The metal tab on the regulators faces in the same direction as the thick line on the circuit board. IN this case they all face the tab to the left. I find it easiest to bend the outermost leads gently away from each other in order to hold the part in place while I solder the middle lead. Then I straighten the two leads and solder.

Insert voltage regulators


Bend leads gently, solder middle lead, straighten other leads, solder


Next insert the trimpots. It does not matter which way these are inserted, but I prefer to keep the adjustment screw away from C5 and C6 making it easier to access. I also bend the leads gently to hold these in place while soldering.

Insert trimpots


Bend leads gently, solder middle lead, straighten other leads, solder


AT this point we can add the rest of the components. All that should be left are two electrolytic capacitors and two terminal blocks. Make sure to once again pay attention to which way the electrolytic capacitors are inserted, negatives facing each other.

Insert C4, C5, and terminal blocks and solder


Once you've trimmed any remaining leads all that's left is to give the board a cleaning. I usually simply give it a quick scrub with some isopropyl and a fingernail brush, but there are specialty flux removers and pcb cleaners if your are so inclined. Take a minute to visually inspect all your solder joints and all your parts in case you've made an error while populating the pcb.

You should always test your newly built PSU by itself before using it to power something. Better to find out now that you've made a mistake or have a faulty part than to fry something else in the process. When hooking up your transformer to the pcb there are three connections to make on the input side. Sec1 and Sec2 are your transformer secondaries and are interchangeable and the spot marked GND is for your center tap. Before powering on make sure that your pcb is on standoffs or a non conductive surface. Adjust the trimmers to get the approximate voltage that you want  (for the +/- outputs) but keep in mind you will likely have to adjust again once the PSU is in situ.

Cheers and have fun!
 
The current capabilities are decided by the VA rating of the power transformer you choose and the regulators, which are good for delivering about 1.5A continuously.

What can this supply without heatsinks on the regulators, as shown?
Assuming I wanted +24/-24/+48 and was using a 24v secondary.
 
That's actually a really good question...and something I need to test to give a concrete answer. What kind of current do you need? I usually just add heatsinks for anything aver about 200mA.

http://www.ef-uk.net/data/heatsinking.htm (may not work in chrome...had to use explorer, shudder.)
 
@dmp: a 24vac secondary gives about 33vdc. 33-24 gives us 9 volts of drop. As a rule of thumb, 0.5w is max for a bare to220. 0.5/9 gives us about 55ma of current. A bit less in fact since about 5ma are flowing in the voltage setting resistors. So I wouldn't draw more than 50-60ma (continuous).

Before you ask, why 0.5w ? With no heatsink, the to220 package will rise by 50°c for 1w. On a hot day, it's not uncommon for equipment to have something like 35 to 40°c inside. Half a watt gets you to 60-65°c, which is fine. In fact, we could without worry go up to 0.75w (75°c). Higher temperature will reduce the life of both the regs and of the nearby caps. But you have to allow for mains variations of +10% and a possibly lightly loaded transformer putting out more juice than expected. So 0.5w is nice figure to remember.


This being said, I'm curious... there's no noise or oscillations at the output, checking with a scope ? The fact that the charging currents from C2, C6, C9, C11 have to run the whole board's length and back, passing by the output terminal on their way, seems at first sight like a recipe for disaster.

Well, maybe it's fine and it goes to show how pcb design is mostly black magic.  :-X
 
00940's numbers and advice sound about right from the reading of done on the topic...thanks for the clear explanation.

As for the output noise, that was one of the first things i tested back when i was in school. When i get some time I'll scope it again and post the results. The layout is VERY similar to the green PSU and a handful of others that I've seen as it simply follows the schematic from left to right for the most part with regards to layout. I've never heard (pun?) any noise issues reported with this one or any other like it.

There's a definite art and science to pcb layout and I will not claim to be a master but I'm confident that this particular layout is juuuuuust fine.

Cheers
 
quick question,

for the psu universal how do you wire the secondaries?  with this http://www.digikey.ca/product-detail/en/VPT30-830/237-1326-ND/2090064 

I was going to wire it dual isolated secondaries, per the diagram here http://web.archive.org/web/20090914070140/http://www.diyfactory.com/data/transformer_connections.gif

tie blk/red and orange/yel and connect each pair to the sec 1 and 2 terminal???

the gnd i was going to get off the IEC power inlet terminal, and tie it to a star ground with the grounds on the xlr...

does this sound like a good plan?  :) :) :)

best!
Greg
 
bieckmusic said:
I was going to wire it dual isolated secondaries, per the diagram here http://web.archive.org/web/20090914070140/http://www.diyfactory.com/data/transformer_connections.gif
For your 120VAC mains primary winding hookup you want a parallel config (bottom left side pic of your link).
For your secondary winding hookup you want a center tapped config (fig. 3).
Notice the dots to get winding starts and ends right.

tie blk/red and orange/yel and connect each pair to the sec 1 and 2 terminal???
the gnd i was going to get off the IEC power inlet terminal, and tie it to a star ground with the grounds on the xlr...
does this sound like a good plan?  :) :) :)
At best it will NOT work this way (if your fuse -you want a fuse!- blows fast enough to protect the transformer from your shorted out secondary windings).
Transformer secondary side: black goes to one of the 'SEC' terminals, yellow to the other 'SEC' terminal, the tied together red+orange center tap connection goes to the 'GND' terminal.
Your Triad 25VA transformer primary side: tied together blue+violet goes to switch, to 315mA slow blow fuse, to IEC 'L' and tied together gray+brown goes to IEC 'N'.
(Consider to use a dual pole mains switch for switching the neutral side as well).
Make sure, the tip of the 5x40mm transformer fixing bolt never touches the lid of your conductive 19" case.
 
Thanks again for your help, I found the error last night with some help from Ptownkid.  working great!  I always use the dual pole switch and the fuse.  I wasn't aware that the fixing bolt can't touch the top of the case, is that true of the bottom of the case as well?  The bolt is short enough it wont reach the top but it does touch the bottom.


sincerely appreciated, :)

Greg
 
I finally came across a suitable transformer for racking a DDA channel strip I have and this psu kit seems perfect. I also happen to live in the same town as you Ptownkid. I'll hopefully be ordering a kit this weekend.
 
Ptownkid,
I have to hand it to you, this is probably the best how to I've ever seen.  It would have saved me a lot of time figuring out how to make DIY work.  3nity and others have helped me a lot, too.  Props to all the contributors.  8)
 
mrc said:
Ptownkid,
I have to hand it to you, this is probably the best how to I've ever seen.  It would have saved me a lot of time figuring out how to make DIY work.  3nity and others have helped me a lot, too.  Props to all the contributors.  8)

I ordered my kit today. Seeing this guide is what made me choose his kit over other options.  :)
 
My appologies, it looks like I had been using an out of date email listed on the site. Cheers for getting back to me Brian!
 
I responded to all your pms except for the last which said you were in no rush. That e-mail address is quite old, where did that come from? I thought we were simply going to get together in person sometime instead of you placing an online order. I had no idea that you had ordered as I did not receive a paypal notification. My apologies...I see that you e-mailed me through the site for the first time 2 hours ago, will respond now.
 
I'm liking the lead bender you've got. I'm searching for a file/template for one I can print on our 3d printer at work.
 
Hi there:
I built and 4 channel api preamp, with access 312 and psuniversal, but sometimes my fuse blows at turn up the unit?
The psu have a 25VA power transformer https://system.netsuite.com/core/media/media.nl?id=12594&c=ACCT126831&h=edc46e33aa58dd9d56cd&_xt=.pdf
the power transformer is wired for 220VAC at primary.
i'm using 160mA slow blow fuse

Regards
 
Graham said:
I'm liking the lead bender you've got. I'm searching for a file/template for one I can print on our 3d printer at work.

I actually found a template for one of these and printed it off and I love it.

Anyway, I finally got a chance to build my Psuniversal a couple days ago and it works great! Super easy to assemble. Took less than two hours even for a noob like me. Time to rack my DDA channel strip, maybe add a DI input, and probably use it for bass preamp in my rig.

Awesome kit!  :)
 
Hey guys, I think I must be having a massive brain failure. I had an issue a while back with having over 100V at my phantom output. Ptownkid rightly suggested a blown LM317.  I was overloaded with recording projects for a long time and am just now coming back to projects I hadn't finished. This includes two projects using the PSUniversal. Both are having the same issue. I'm using the VTP36 transformer in both projects. Both with primary leads in parallel for 120VAC mains, and both with secondary leads having orange and red tied and run to GND, Black and yellow to their respective SEC1 and SEC2. Power rails are just fine, but both are blowing the 317's. They'll run fine at first at a solid 48V, but before I get everything sorted and screw the cases on, the phantom in one of them hits 100v, the other is about 80 right now. AC input seems fine, but without fail, my phantom goes up eventually.  Has anyone else had this issue? I'm using clip on heat sinks for the 317's on both. Would the screw on type help? or is there something blatantly obvious I'm missing?
 
The tab is live on these devices, so the heat sink needs to be isolated or insulated to prevent shorting to other components or to ground.  Have you checked for shorts?
 

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