modifying SSL9K psu for EZ1290

Making a new topic for this as it doesn't fit quite in anywhere else, although a very similar question has been asked here:
http://www.groupdiy.com/index.php?topic=35947.0

Basically, I want to modify a spare SSL9k PSU board to provide me with single 24vdc for the EZ1290 as well as 48vdc for phantom power.
I have read the above thread with interest and also browsed the JLM forum, but I don't quite understand the JLM mod as it is only described on the pcb and not the schematic. I understand they are replacing one cap with a jumper to disable the negative rail and there is an additional jumper that connects "a" capacitor to "a" diode - but which?

On the schematic below, I believe I managed to figure out the 'jumpered cap' bit in regards to the SSL9k psu, but I feel I am missing the second jumper, which I believe connects to the point marked "?". What node do I need to connect this to? Or am I barking up the wrong tree altogether?

(hope it is ok to borrow the ssl9k schematic...original schem is here:http://www.studio21.ch/diy/neeno/ssl9k/DIY_9k_Preamp.pdf)

The mod for the JLM psu is only for people using a single secondary trafo. If you use a 2x 24VAC trafo with Keith's PSU (or JLM's for that matter) you don't have to modify anything. Just leave out the negative rail components.

sorry, I guess I wasn't clear, I do want to use a single secondary transformer (or alternatively 2*12V in series) as I don't see the need to buy a bigger transformer when half of it sits unused....also physical size is a consideration in a 1RU build.

this edit should do it for a single 24VAC secondary.
If you want 48VDC out, change R2 from 240R to 220R, else this R1/R2 network is set for 44VDC.
An additional  6K8 load resistor will draw the missing 7mA to meet the 12mA min.load current for your regulator if no other load (phantom switched off) is connected. All polarized caps (C1,C3,C4,C5) need an at least 50V rating with 24VAC secondary in front. (the 35V one might blow at 10% high mains or with transformer unloaded, no need for 100V rated caps, if size matters).
Good luck
-Harpo

Harpo - thanks so much for this.
There is a bit of a squeeze round the capacitors on the ssl9k board, but with the negative rail missing (and the regs fly-wired to the casing) I should be able to fit it all in.
Nochmals vielen dank  ;D

briomusic said:

to the point marked "?". What node do I need to connect this to? Or am I barking up the wrong tree altogether?

Click to expand...

That ? should reference to the 0v ..24v supply rail............no return current possible for the regulator otherwise..
no 48v is the result.

Harpo said:

this edit should do it for a single 24VAC secondary.

Click to expand...

Something bothering me about this ?

Hi S2udio,

after studying the schematic of the famous JLM ACDC PSU http://www.jlmaudio.com/ACDCVer2sch.pdf,
the circuit suggested by Harpo seems quite similar to the ACDC in 'tripler' mode.

As (I think) you say, the "?" should reference to either the 0v or the 24v rail, Harpo's version is referenced to 24V if I understand correctly.

What is bothering you about the "?" ?

If anyone would like to have a look over my PCB mod picture - red indicates missing component or cut trace, green indicates a jumper.

cheers
briomusic

should work.
Dunno if s2udio is bothering about my editing in red instead of blue, maybe its about missing safetybelts around the LM317HV / TL783 or not showing a crowbar ...