PSU preamp troubleshooting

[Blondino]

Hi y’all… long story short, I’m making a simple mic preamp with his own PSU, putting down hold fashion with a breadboard, and my eyes are crossing already
Everything good so far, but is never late for rookie mistakes.
I stuck on the psu. A +-16v and 48v power supplies, schematics are reliable. Using LM317 for positive and LM337 for negative.
I got it to work. +16 good, +48good, but -16 had a problem. The DMM stuck on -25v and adjusting the trimpot won’t make any difference.
After a quick analysis I realized I put the same Vin and Vout on the 337 like if was the 337 (dho), so I simply desolder the trace and routed in the correct way. Full of hope I turn it on, measure the output voltage. +16 good, +48 good, -25v: trying to adjust the trimpot and nothing change again.

I checked several times if tte adjust section is correct and yes it should be fine.

The only thing jump in my mind is if the 337 now is bad. But still regulate the voltage well!
Anyone went trough similar steps?
Thanks in advance

 

[dmp]

Sounds like the LM337 is wired wrong. Link to the datasheet of the LM337 you are using (i.e TI, ONSEMI, etc)
And post the schematic
If everything were correct it would be working

 

[Blondino]

Well, this is the schematics I recreate, now the 337 in and out are connected right but, again, the trimpot doesn’t lower or neither raise the voltage, and it stuck at -25.something.
I havent’t replaced the 337, I checked the trim and values are fine.
If nothing come up, I will try to replace every components

 

[dmp]

The diode bridge should be connecting to pin 2 also.

 

[ccaudle]

The electrolytic capacitors are drawn reversed. Are they installed correctly, or matching the schematic?
Have you double checked the diodes are installed correctly? Diode1 is drawn correctly, but if installed backwards it would create the effect you described.

 

[Blondino]

I’m sorry I made a mistake drawing on paper. This is how everything is connected. D1 is connected right but I do still have that effect, the trim won’t regulate anything

 

[ccaudle]

Did you ever replace the LM337 component? Perhaps it is no longer working after you connected it backwards. At least I assume that is what you did, I think your original post had a typo ("I realized I put the same Vin and Vout on the 337 like if was the 337"), which I assume you meant to say that you connected the 337 as if it were a 317.
Just go back to the basics, measure the voltage at each pin of the 337, that should give an indication of what is not working properly.

Make sure D2 is not installed backwards, there should be 1.25V difference between the output and adjustment pin, if D2 is the wrong orientation it will clamp that at around 0.6V or 0.7V and the regulation won't work.

 

[dmp]

I’m sorry I made a mistake drawing on paper. This is how everything is connected. D1 is connected right but I do still have that effect, the trim won’t regulate anything

If you had everything correct it would have worked.
For people here to help you, take the time to draw a complete accurate schematic and post a picture of your build

 

[amplexus]

There is a greater than zero chance you've fried the reg. Now that you have corrected the wiring to the 337 terminals, replace with a known good device and try it again.

 

[Blondino]

Yes correct, I received new 337. I replace it and now is finally working.

I will post some pics once I designed insert stuff on the computer and start drafting the PCB.
Thanks again

 

[Blondino]

Here what I did since last time:
This is the schematics I used and I add a LED. Just ON/OFF purpose. I connected the LED to the +16V to chassis (a friend advise me to do that so it won't have interference with the PSU's ground).
I put a 1k5 resistor. Should be enough. If my math was correct, based on the LED I have to be at maximum bright the minimum value was 680R, so I just keep it safe putting a big one.
Sorry for the diode bridge, since I used regular diodes the software didn't allow me to put them at some 45 degree angle.




Then I draft the PCB this way. keeping the AC insert on the right hand side and the trimmer on the lower side of the board so it will be on the same side of the toroidal and the trimmer will face me. Also I kept a "big" output on the left hand side and I add 4 more on the bottom. My idea is to power at least 4 preamps.
I could fit everything on a 140x60 mm board but I actually think the heatsink are a bit to big for this project and i would like to put smaller ones. Is that I haven't other footprint to use and I need to create some more, also I don't really know how to calculate heat on a regulator.
I don't think it would make it much smaller but if someone have advise please welcome


I almost forgot, is always nice to see a 3D model