LM317 based PSU for 48v troubleshoot

[moamps]

Are you saying that the - of DB2 should not connect the + DB1 and instead go to ground?

Yes,
look into schematic from JLM site you already posted.

 

[ohm]

ok now I get 36.1v  :'(

 

[moamps]

That's too low. Go back (disconnect - of DB2 from the ground and connect them to the + of DB1),
and use a higher voltage rated capacitor for C8, or use two caps in series as it's done
on the JLM schematic.

 

[abbey road d enfer]

hmm voltage on + of C8 is around 71

Connect - pin from the rectifier bridge DB2 to the ground and recheck voltage.

In that case, the unregulated voltage will be insufficient - not a doubler anymore.

 

[abbey road d enfer]

hmm voltage on + of C8 is around 71

Looks like I need higher rated capacitor than current 63v?

Alternatively, you could connect negative of C8 to positive of C3.

 

[ohm]

So effectively connect C8 across the in/out of the TL783?

Alternatively, you could connect negative of C8 to positive of C3.

 

[moamps]

Alternatively, you could connect negative of C8 to positive of C3.

C4?

 

[ohm]

C3 or not C3? ... that is the question :-\

 

[abbey road d enfer]

Yes, C4.
Sorry for the typo!

 

[ohm]

hmmm ok

negative of C8 longer goes to ground, it goes to positive of C4

negative of DB2 goes to positive of DB1

essentially negative of C8 and DB2 join together and go to positive of DB1

Still I get 71v at positive of C8 

 

[mjrippe]

So use a 100v cap!

 

[ohm]

may as well order some other parts then... and set the correct resistor value at R2

thanks all!

 

[abbey road d enfer]

Still I get 71v at positive of C8 

Yes, but voltage across it (i.e. between pos and neg lug) is reduced by half.

 

[tubegeek]

Shall I put 100k in parallel with C8 then?

After a second look, I notice that the combination of R1 and R2 will bleed the charge from the 48V supply, and the combination of R3 and R4 will bleed the other supply. So no need for any additional resistors.

Use your law 

moamps is right, it is a nice law you've got there, by the way, thanks for that one!

 

[ohm]

Yes it is 36v

So this PSU is ok then?  8)

Yes, but voltage across it (i.e. between pos and neg lug) is reduced by half.

 

[ohm]

Yes it does, the 48v slowly drops away at switch off...  8)

After a second look, I notice that the combination of R1 and R2 will bleed the charge from the 48V supply, and the combination of R3 and R4 will bleed the other supply. So no need for any additional resistors.

moamps is right, it is a nice law you've got there, by the way, thanks for that one!

Well thank you  .... but I am only a messenger for the higher forces of the universe. Now repeat after me.... ooooohhhhmm... ;D

Thanks for everyone's help.

I'm sure I'll be back i dues course to try fix the cross talk on my summing amplifier

 

[abbey road d enfer]

Yes it is 36v

So this PSU is ok then?  8)

What do you think?

 

[ohm]

I believe it is. It spits out 24v and 48v and there is 36v across the +/- of C8

AND it hasn't started that filthy habit of smoking again...

We'll see properly once it's powering the preamps

 

[ohm]

Would like to add that this is a most helpful and patient community and I really appreciate the input that was given

I've learnt a lot from this.

Following existing diagrams for building the preamps was one thing, but it's not until you start trying to modify designs or even create fresh circuits do you understand whats really involved

Thank you!

 

[abbey road d enfer]

I believe it is. It spits out 24v and 48v and there is 36v across the +/- of C8

AND it hasn't started that filthy habit of smoking again...

We'll see properly once it's powering the preamps

Good!