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

[fucanay]

Ok, I did some tests. I pulled D4 out (third 1N4007) and jumpered it from there. I also move the 100V rated cap (C13) to the space for the second 63V (C12) and left C13 out altogether.

The output of D2 was 49.2V and the output of D3 was 64.5V. The +48V output now reads +46.4V, which is plenty.

While I was probing around, I decided to check the two big caps at C1 and C7, which are both rated 1000uf 35V. But C1 is seeing 50.2V, so that is going to need to be upgraded to a 63V cap. I'm not sure if I have one, but I'll look around. C7 was only seeing 23.9V so the 1000uf 35V should be ok.

Anything else I should test to make sure this is all ok?

Edited for my mislabeling .

Matt

 

[originalmusician]

Good idea on checking the voltage getting to those caps. I totally overlooked that :idea:

 

[fucanay]

Turns out this 15-0-15 transformer is too much. The voltage regulator for the +24V is getting smoking hot. I put a chunk of Aluminum on it and that gets smokin hot. The output of the 15-0-15 is actually 37V wired in series, so it's having to drop 13V plus whatever the bridge rectifier adds.

I need to order a 12-0-12 for it. I think that will be much better. Stay tuned.

Matt

 

[Ptownkid]

what regulator are you using?

 

[fucanay]

It's the LM317 regulator. For the record, the regulator didn't blow, but it's getting WAY too hot.

Check out the first post in this thread for all of the details for how I've modified the PSU to work in this config. I'm actually going to change the first post more soon. I need to show where I changed one of the 1000uf caps to a 63V and where I removed one of the Diodes because it was giving too many volts for the +48 regulator.

Matt

 

[Ptownkid]

Unless I'm too tired to be thinking straight, I have a feeling that you're exceeding the Vmax of that regulator. It's supposed to be adjustable up to about 37Vdc, which means that you need about 39Vdc to get max output. You're feeding it about 52V right? 37Vac x 1.414 = 52.32Vdc

So doing the 12V secondaries in series would be a good call, unless I'm missing something. The other route is to what matta said and use one secondary and center tap of a higher voltage xfmr.

 

[fucanay]

I don't fully understand how these regulators work, but the phantom power is run off of a LM317 also. But maybe in a different manner. Need to look at the schematic some more.

Either way, I'm getting it too hot. So I'm going to order the 12-0-12. I need to get different pots anyway. I order logs instead of linears.

Matt

 

[Ptownkid]

[quote author="fucanay"]but the phantom power is run off of a LM317 also. But maybe in a different manner. [/quote]

Good point...

 

[peterc]

If you look at the 317 datasheet, you'll see that the Output voltage - Input voltage differential is 37v, so as long as you do not exceed this, you're OK. So you can float the reg at a higher voltage, just dont exceed the differential.

The TL783 reg is only a 120v part, but Jakob uses it in his G9 power supply which runs at 245v. He does some clever protection with zener diodes to make sure this differential is never exceeded.

Peter

 

[Ptownkid]

[quote author="peterc"]If you look at the 317 datasheet, you'll see that the Output voltage - Input voltage differential is 37v, so as long as you do not exceed this, you're OK. [/quote]

Thanks Peter, makes more sense now

this is straight from the datasheet text

Since the regulator is “floating”
and sees only the input-to-output differential voltage,
supplies of several hundred volts can be regulated as long as
the maximum input to output differential is not exceeded, i.e.,
avoid short-circuiting the output

Can you tell me what parameter on the data sheet tells you that the differential is 37V

 

[originalmusician]

[quote author="originalmusician"]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.[/quote]

I thought I would put an update on this. I blew the LM317 on the 48v again. So despite the heatsink, I'm still blowing the regulator. Interestingly, it works for awhile, and sooner or later, it blows. I'm thinking the 65v I'm feeding it should work fine for this application. I don't believe I shorted the heatsink to ground, as the previous regulator I blew didn't use one. Maybe I'll try a 60v HR type in there, but that probably won't make a difference. Other than that, I'm not sure what to do? I noticed a few old posts where other people have had problems blowing this regulator though.

BTW, I think the input/output differential is stated as 40v at absolute maximum?
http://www.ortodoxism.ro/datasheets/nationalsemiconductor/DS009063.PDF

So I guess the 1.2 to 37v is the actual range you would want to use?

 

[veermaster]

Hi Fucanay,
on the first page you wrote that you still have problems with the 48V supply. Is that still the case or is the PSU running ok now the way you posted it?
Thanks a lot, Emre

 

[fucanay]

I kind of stalled on all my projects due to some back problems and a potential surgery for them. I think I explain the +48 on page 3 and that was fine. My remaining issue was the need to replace the 15-0-15 transformer with a 12-0-12 to get the heat down on the regulators. But I've lost my job and my health isn't doing so good right now, so I've been out of the game for a little while. I hope this helps, but I'd have to actually try it again to be sure.

Matt

 

[veermaster]

Hi Matt,
I´m really sorry to hear that and hope you will be better soon!
All the best, Emre

 

[fucanay]

Surgery is done, DIY is somewhat back on.

I just hooked up the 12-0-12 transformer (Avel Lindberg PN: Y236102) and everything works great. I had to put D4 and C13 back in, as the +48 was really in the mid 30's. Everything in the first post should be good to use.

Hope this helps someone.

Matt

 

[veermaster]

Good to hear you´re fine.
And thanks for the info....
Emre

 

[gswan]

[quote author="peterc"]If you look at the 317 datasheet, you'll see that the Output voltage - Input voltage differential is 37v, so as long as you do not exceed this, you're OK. So you can float the reg at a higher voltage, just dont exceed the differential.
[/quote]

However this can easily be exceeded on power up when there's a sizeable capacitive load on the output (which appears as a short circuit on the output until the caps start to charge). It's also a recipe for disaster when something unexpected happens, as pointed out a short circuit on the output from some other failure or accident.

Would you really trust your very expensive condenser mics to something as dodgy as this?

 

[3nity]

Matt. Are you using a 24CT transformer? or a dual 12-0V transformer?
If i understand well your schematic, you join both 0V together?
I am racking my pair of Fetboys and planning on future use for some 1272 comming soon...

 

[originalmusician]

[quote author="originalmusician"]
I thought I would put an update on this. I blew the LM317 on the 48v again. So despite the heatsink, I'm still blowing the regulator. Interestingly, it works for awhile, and sooner or later, it blows. I'm thinking the 65v I'm feeding it should work fine for this application. I don't believe I shorted the heatsink to ground, as the previous regulator I blew didn't use one. Maybe I'll try a 60v HR type in there, but that probably won't make a difference. Other than that, I'm not sure what to do? I noticed a few old posts where other people have had problems blowing this regulator though.[/quote]

Since this thread has been resurrected, I'll provide an update. I used a heatsink gasket, and all is fine now. Interestingly, the first LM317 I blew didn't use a heatsink. The second with a heatsink and no gasket blew after a few hours (eventually shorted due to tight space and handling the PS). And the third with a heatsink and gasket has been rock solid for months. :grin:

 

[3nity]

i always put a Heatsink on the LM317 when used with for phantom...due to input voltage differential......