Power Supply Upgrade

I just pruchased the Cambridge Audio 540P phono pre-amp and have to say that I am pleasantly surprised with this little piece of kit.

My quest now is to upgrade the 'wall-wart' style external power supply. It has the standard UK input voltage but the output is rated at 12v 500mA, but here's the interesting thing; there is a synewave symbol beside the 12v which would indicate this is still ac. I was expecting to see the dc symbol, so if anyone has any knowledge of this or what other type of power supply upgrades (kits are acceptable) I would be very grateful.

Would also like to upgrade the bell-wire type cable that runs up to a dc type plug too.

 

You sure it doesn't mean "around" as in ~12V approximately 12V?

 

Use a multimeter to check it .....or have a look in the phono pre for the rectifiers and voltage regulation. It's quite a common wat to go .....and so simple to upgrade just get a 50va 240vac tranny [toroidal or laminated] from RS of the right voltage. Box it up to prevent death by electricity, and there you have the start of your upgrade path. Then you could look at the diodes..........

 

Hi there, thanks for the replies, I can confirm that the ~ symbol is to the right of the 12v on the rear on the phono amp but not marked on the wall-wart plug.

I checked the voltage from the pin (dughh, should have done this before!) and on the AC setting I have a reading of approx 14v and on the DC setting approx. 0.01.

This does then seem to appear to be a 12v AC power supply, so has anyone got any ideas about a suitable audio quality 12v AC power supply or kit?

 

As zanash said, you can cut in a few caps around the 3300uf value, de-couple with 220nf etc and you'd have a decent psu. Id check what regs the phono is using first. Out of interest, how where does the phono pick-up earth?

 

My bet would be a good 10 to 20 va 240v 12vac from RS.... a nice box an IEC inlet with a dc out socket or flying lead to the the phono stage. You could look at a good mains lead as well.

Then you could attack the rectifier change the doides for 11DQ10's or simmilar schottky diodes, look at the resovoir caps swap if there bog standard type for a minimum stagets then bypass with values of 10%. look at the quality of the signal connections change if nessesary. Look to see whats in the signal path opamps theres a good place to add better components, what resistors are there, swap for vishays or holco's......the list is endless and you have not even altered the curcuit !

 

...I should have said that I am not an electrical engineer so all this shop-talk is a little over my head!

I was purely looking to see if anyone has a standard kit they build themselves, whether there is an off-the-shelf kit, or whether they know of any other power supply upgrades similar to something like the Monolith unit in the USA (as used for Perpetual Tech gear)?

 

The superDAC similarly uses a 9V AC power supply. It's easy enough to knock up a "toroid in a box" style psu for this (as several members on here have for the superDAC).

 

...if it's easy can you give the details then?

 

check out sid and cokes website, he's built a simple psu to power an MF product.

 

Took a photo of the phono circuit so you guys can take a look to see what you think!

 

So is this the new thing with the funky box? Looks neat.
Stuff on the left, behind the screen and possibly heatsink for the regs/diodes/whatever, looks like the PSU so you could try changing the electrolytic caps for something better.
When choosing caps don't worry about voltage, as long as its greater than or equal to what is in there you'll be fine. Try black gates or something.

The Transformer upgrade is literally just a transformer in a box. If you can get inside the wall wart you have now you should be able to see, its nothing clever. If you just take the existing cable off that and connect it to a bigger transformer then it will hopefully improve. If you search the RS website for '12V Toroidal transformer' or something along those lines you should find something suitable. Bigger VA rating is better. But I wouldn't bother with anything over about 30 odd for this.

 

Thats a straight forward enough phono pre using a common layout of resistors for the RIAA side of things. Its better than I imagined it would be for the money and Id put money on that it will outperform the nad and project competition. It looks like the regs are close to the first op amp (bottom right) which is a good thing. What op amps are they using? (just read whats on the top). If you ever get upgradeitus theres plenty you could do and it all looks easy to work with. Id look at the op amps first as this is an area cost can be cut. Theres a decent amount of caps for the power supply (left hand side) so Im sure a simple transformer in a box will yield decent results.

 

Typical, I never checked the details on the Op Amps, I will get on to that today, but here's what I did take note of:

Power stage:
C1 through to C6 are Acon -40 degrees C - +85 degrees C, 220 micro F 50v
C11 NCD RGTX 105 degrees C 10 micro F 25v

Main Circuit:
(the large brown caps) C12, C13, C27, C28, C29, C33
<>CL21 475J100T
C9, C10, C16, C17, C20, C21 NCD RGTX 105 degrees C 25v

C24, C32 Acon -40 degrees C - +85 degrees C, 100 micro F 25v

If there is anything else you guys might need the details of let me know, would be glad to provide it.

By the way, got it this set up with the Rega 3 at the moment and it sounds much better than the entry level Pro-Ject phono box that I have used before.

 

Plenty of scope to hack about ..........replace and bypass all electrolytics IMO don't use black gates you'll still be waiting for it to run in this time next year. Lots of resistors to change for vishays or holco's. Some nasty looking sockets to rip out swap for any decent ones even the ptfe one from maplins will be better.

Opamps pullout fit some nice berylium copper sockets and swap for the very best your budget can afford as these will sculpture the sound.

Swap the diodes for schottky's and you'll start to get a decent performance from the beast.