Using Green Pre PSU as FETboy PSU? (and why you shouldn't do it)

[fucanay]

[quote author="fucanay"]Is is just a matter of combining the two 15V wires? That kind of scares me as I don't know for sure that's how it works.

Matt[/quote]

Yeah, that was wrong. :shock: I almost burned up the tranny. I think I've tried all of combinations I can think of. Maybe it's not possible to get 30 volts from this thing. :?

Matt

 

[Ptownkid]

If you connect red and brown together, you will get 30V between green and blue

http://www.amveco.com/Miniature_Low_Profile_Transformers_2.htm

 

[fucanay]

Ok, so I used my multimeter to measure between the green and blue. It came to 37V. But how would I then connect that to the board to make it usable. Would the two 15 volt leads go to one pad each and the red/brown remain unconnected? Do I no longer need a zero reference because I'm referencing between the green and blue?

Sorry for all of this. I'm really trying to understand, but I'm missing something really fundamental and it's driving me nuts.

Thanks Bryan.

Matt

 

[originalmusician]

Okay Bro, you are almost there.

<<<I missed your reply and went ahead and built the thing. I left the 220R as it was and changed the R1 and R2 to 2k. I got the numbers using the calculator.>>>

That's cool. So you have a total of 4k out of R1 and R2.

<<<<I paralleled the secondaries of the transformer and it only measured 18.3VAC. I went by the instructions for my transformer, listed here. The part number I'm using is 62063. I don't know what's wrong here. I tried two transformers and they both measure the same. Probably my stupidity, but I don't know where.>>>>

Well, that is what I expect as your transformer is rated at 2 x 17.8v. So your hookup and measurements are fine. The problem is that you need to connect the secondaries in series. Keep in mind that paralleling the secondaries keeps the voltage the same and doubles the available current. Connecting the secondaries in series doubles the output voltage but keeps the available current the same as one side.

<<<<<Speaking of stupidly, I did check the DC volts coming out before I checked the AC volts coming in and it's not that far off on the +24V. It came in at 22.9V. The +48V came in at 24.5 Volts, but I didn't put one of the 1N4007s in, thinking that I might blow the regulator if it was too high.>>>

I would put the 1N4007 back into the circuit, as looking at the circuit it appears to be necessary. After some checking it turns out the LM317 can easily handle the voltage that you are throwing at it as long as it is getting clean DC. Clean voltage will not blow the LM317 out, but overpowering it will. IOW, your transformer is rated at less than an amp and should be okay with the regulator.

Like I said before, I'm not an expert at these matters so anyone else's input is appreciated. But the above is how it appears to me.

Edit: Hmmm, I see I have posted long after others have already replied. That shows about how together I am tonight. My girlfriend is telling me to log off and give her attention, so I gotta cruise for now. I'll look at this thread again tomorrow after work.

 

[peterc]

Fucany

Check these 2 links, they will help with setting up the PSU

http://www.groupdiy.com/index.php?topic=10005&postdays=0&postorder=asc&highlight=green+current&start=0
http://www.groupdiy.com/index.php?topic=199786#199786

Peter

 

[fucanay]

Thanks for the links Peter. I can't believe that I asked that questions so long ago and still don't understand. This graphic shows what I want to do, but I'm unclear how to hook up the leads to the board.

The data sheet says this:

To parallel the secondaries, connect green and brown wires and red and blue together. To connect the secondaries in series, the red and brown wires are connected together. Take the output across the green and blue wires.

The only way I see this is that I'm supposed to hook up the Green and Blue up to the two pads as in picture matta made for me. Now when I stupidly hooked the Green/Blue together before, I got zero volts and HEAT, just like you said in the other post. So with the way I am trying to use your board, would the green and blue both go to the inputs of the bridge and then combine once in DC? And would the red/brown not be connected to anything?

I feel so dense right now. Thanks for all of the help.

Matt

 

[Ptownkid]

You got it

 

[smallbutfine]

Yep, hook up green and blue to the psu pcb and isolate the red-brown connection. you get one secondary that has a voltage sum of the two original secondaries.
These things look sooo easy if you do a paint-by-numbers psu, but can really be hard to get the first time you improvise building a psu...
After breadboarding some PSU's with single / dual secondaries, voltage doublers or even triplers, zeners, regulators, bridges or dedicated diodes etc and actually doing the math for it, it all gets easy again and you may 'think' a psu out-of-the-box.
Human brains sometimes need a 'breakthru'-moment after days of frustrating headaches...

Nice you got it! :thumb:

Kind regards,

Martin

 

[fucanay]

[quote author="Ptownkid"]You got it[/quote]

Really? OK. So now I have another question. In the edited schematic, it shows one output from the bridge going to the +24 rail and the 0V going to the ground. But now I have 15 coming out of each side, so doesn't that now turn the ground into an unfiltered/unregulated 15V rail? Does one just automatically become the reference side just because of the way the circuit is built? I'm almost there, but I don't want it to just work, I want to make sure I get my head wrapped around it too.

Newer edited schematic

Matt

 

[Ptownkid]

you have to think of one of the two wires as being ground now. When you measured the 30V between the green and the blue, one of the two was connected to the common or ground terminal of your meter right?

You don't have 15v coming out of each wire, you have a potential of 30V BETWEEN them.

A few more custom psu's and you'll have a grasp.

 

[fucanay]

Ok, I think I've got it now. I'm going to wire it up like this tonight and give it a try. I've learned so much in this thread and I have all of you to thank for it. But this does not end my quest to understand this more completely. If I can't get past this stuff, I'll never be able to understand the rest of it. Little by little, I'll get there.

Matt

 

[fucanay]

I wired it up and tested it. +23.9V and +47.9V. doesn't get much closer than that.

Thanks everyone. I'm going to compile all of this information and add it to the top post. Maybe it can go in the PSU Meta. There is a lot of good links and advice in here now. At least to people like me who just don't get it.

Thanks again.

Matt

 

[Ptownkid]

Way to go man, I'm glad it worked out annnnnnnd you learned something along the way. :thumb:

 

[originalmusician]

Good Job! Out of curiosity, what is the voltage feeding into the LM317 input for the 48v? Also, did you use a heatsink on the 48v reg?

I thought I would post this (from JLM Audio), as I found it relevant and interesting?

"If you are fixing a 48v rail on a old one of our supplies that has a zener change the 39v zener to a 1N4002,4,7. As after finally getting some real detailed info on the LM317 it was found that the LM317 uses its internal regulating transistor with a internal zener to clamp the reg in and out to only drop 40v (or 60v on HV types) between these two points and as long as the current doesn't exceed the regulators maximum of 1.5amp the regulator will be protected. This is why the new supplies have a 47R 2w resistor in series with the reg input pin to limit the current to about 1amp on the 48v rail. Lots of people seem to think that the LM317 can only take 40v input volts safe and that they need HV 60v types but this is not the case. You could use a LM317 at 300v as long as the unreg dc ripple was less than 40v and the current was limited with a resistor so on power up when the reg was in 40v clamp mode it maximum current rating of 1.5amp wasn't exceeded. "

http://www.groupdiy.com/index.php?topic=16738&highlight=lm317+40v

 

[fucanay]

Whoa, good call. Voltages are way high. While nothing has blow yet, I'm sort of surprised. After the last 1N4007 it was around 94 volts. It was around 63 volts after the second one. I think I'm going to try removing the last one again and move the 100V rated cap to that spot. Maybe that will bring things more in line with what it's supposed to be. Either way, 94 volts is way too high. More investigation needed.

Matt

 

[originalmusician]

That sounds like it will work. If not, you could move the 100v cap down and put one with a little more protection in its place. Based on what JLM said, the LM317 should be able to take the voltage (as long as you heat sink it). But using 94v, the caps along the way are a little suspect. And you sure don't want to fry the regulator because the 63v caps on the other side will be getting the full 94v.

edit: I believe you should heatsink all your regulators. I just made some quicky heatsinks out of scrap aluminum for a Green Pre PS running 15-0-15, and they are working well. A small percentage of the LM317's are subject to early failure. My last one in the 48v position only lived for about 5 minutes. I was feeding it ~65v. I'm not sure if I got a bad LM317 or not, but the one I have in there now with a heatsink is doing fine so far. Not using heatsinks when doing significant voltage drops will lead to short lived regulators. They might make it a year or two, but I think it is nice to heatsink them and be done with it. I'm finding out that having to go back to a project I thought was done rattles my cage a little. I think it's because I'm supposedly a musician, but it seems like I never have time to play.

 

[fucanay]

Yeah, that would probably work. But why make the regulator work harder than it needs to. And for the future, I wouldn't want to use more parts than I need. So taking the last 1N4007 out and moving the 100V cap to that position is probably all that's needed.

Also, using the 15-0-15 transformer, I'm actually getting 37 or so volts. I really don't need a trippler in that case. I'll mess with it some today. Change/remove some parts and leave it on for a while longer to see if they really need heat syncs.

Matt

 

[originalmusician]

Yeah, I agree your way looks better. Actually I'm glad you have been doing this because I have learned a lot from thinking about it.

 

[fucanay]

[quote author="originalmusician"]Yeah, I agree your way looks better. Actually I'm glad you have been doing this because I have learned a lot from thinking about it.[/quote]

I don't really know what I'm doing 100%. I think I've got the hang of a lot of this, but the transformer wiring was the major hurtle for me. I wish I had a 12-0-12 transformer (62062 at digikey) here to test it's results too. The real reason for me doing this was for the FETboy preamps and the fact that I had this PSU board and the 15-0-15 transformer already sitting here. So I've learned a lot by doing this too.

I'm still waiting on some front panels before I can get these things all finished up. So it'll be a little while before I get it done. Maybe I should build a little test case so I can actually try these with this PSU. Soon, soon.

Anyway, will report back later.


Matt

 

[originalmusician]

I stuffed my 24v PS into a cheapo Radio Shack project box and put multiple DIP output plugs on it. This way I can feed current to multiple mic pres and not have to mess with building separate power supplies for each one, isolating the transformers, etc.

The box I used is here:

http://www.radioshack.com/product/index.jsp?productId=2062285&cp=&sr=1&origkw=project+box&kw=project+box&parentPage=search

I don't know if that's a good approach or not, but I'm a lazy cheapskate :grin: