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Naim XPS PSU - DIY alternative

G

gustavm

pfm Member
Hi - I am a first-time user.

I recently had the chance to try an XPS2 with my CDX2 & can confirm the improvement is very substantial. A while ago there were some posts about diy construction of a naim XPS. Just wondering if anyone built one, and if they'd like to share any tips?

Voltages (+/-22v, +/-10v, +15, +15) and Burndy pin-out seem to be common knowledge. Looking at a picture of the inside of an XPS (e.g. http://www.acoustica.org.uk/t/naim/powersupplies.html ) it really doesn't look like £2.5k's worth - just a big torroidal transformer, but otherwise standard parts. Not sure what's different about an XPS2.

I was thinking of building one, erring on the side of a bit more over-engineering than used in the real XPS2, but would appreciate any views on the following:

1/Transformers - I have heard that torroidals arn't always the best choice for low-power audio applications because their wide bandwidth lets high-freq mains noise come streaming through. Any views on best choice? I was thinking along the lines of some off-the-shelf non-torroidals, perhaps having to use 2 or 3 separate transformers as its unlikely I'd find enough windings of the right voltages on just one.

2/Rectifiers - I've heard Schottky types are best, but is this simply overkill for this application? (I would need possibly 16!) Would conventional bridge rectifiers be much different?

3/Ordinary cheapo regulators or super-regulators? Would the latter be over-kill, seeing as the CD player re-regulates internally using standard parts? Which rails would most benefit from a super-regulator

4/Electrolytics - how big?

Any tips most gratefully received....
 
I have build several.

You can either go the Naim way and use 317/337 or better use super regulators instead.

Be aware that the +15V usues high current and will require heatsink

You'll need to find a case somewhere and the connectors can be found at Farnell (not cheap...)
 
Teddy -

I'd be interested to know what different designs you tried, and how they compared sound-wise.

Also - which Naim player you have, and whether you had a chance to compare with an XPS or XPS2.....
 
Many thanks - some really useful stuff. I'm inclined not to modify the CDX2 itself for the time being, but thinking of building an XPS clone based on 6 super-regs. I had a look through these threads - I may have missed it, but what did you use for the Burndy cable? (Even these are £300 from Naim)
 
gustavm said:
but what did you use for the Burndy cable? (Even these are £300 from Naim)
Click to expand...

Silver coated wires

Not sure it's worthwhile to use that many SRs, as they are followed internally by simple 317/337 anyhow. Good quality VBEs will give you greated effect.

Be aware that the current is high on the +15V. Use a power rail that will not require too high dropout and use heatsinks
 
Teddy,

I've just measured the currents. My meter only displays to 10mA resolution but I get:

+22v - 50mA
-22v - 40mA
+10v - 30mA
-10v - 80mA
+15v (digital + clock etc) - 290mA
+15v (motor, servo etc) - variable, 280mA steady with CD playing, but peaking to at least 600mA on track search etc.

On that basis I am planning:

+15v (motor) - standard LM317 regulator with heatsink

+/-10v & +/-22v - ALW super-regs per rail.

+15v digital - ALW super reg?

You suggested that I'd be better off with a good quality VBE - i.e. does this mean a one-transistor capacitance multiplier in front of the SR?

Also - for the +15v digital - the super reg manual suggests it can handle at least 200mA, possibly as much as 500mA. Am I safe to assume 350mA is definately OK?
(I'd aim to keep the voltage headroom sensible & will use heatsinks)

Any other comments? Realise this may be over-engineering a bit, but still probably only ~1/10th cost of an XPS2....
 
gustavm said:
Also - for the +15v digital - the super reg manual suggests it can handle at least 200mA, possibly as much as 500mA. Am I safe to assume 350mA is definately OK?
(I'd aim to keep the voltage headroom sensible & will use heatsinks)
Click to expand...

In another thread, we've got guys there who are running Squeezeboxes off a single ALWSR and the squeezeboxes are drawing at least a steady 780mA when idle, peaking over 980mA and drawing a steady 920mA while playing. I'd say 350mA is pretty safe! Just make sure you strap the 2 ICs to a damn chunky hunk of metal... when I do mine, I've got a 6" x 1" x 1/2" chunk of steel I'm gonna use, and that's gonna be bolted to the chassis of the psu! :D
 
Gustavm,

Yes, you design seems OK, for the 15V superreg use a heatsink.

If you replace the ALWSR pre-regulator with a VBE it can drive several Amperes (with a heat sink). I'm actually working now on a project to super-regulate my power amp. More on that soon...
 
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