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RE: All supply is now Linear except for Pico PSU

Ultimately, that is my intention. But I don't have a clear roadmap yet.

Bear with me while I think out-loud...

I'm currently focusing on the D-to-A conversion... I've been using a stock Juli@ and it's analog output. While I'm getting exceptional sound already, I feel there are some significant gains to be made there. My 'Juli@ Follies' post earlier this week is my prelude to some serious modifications on that card, with the ultimate plan to power it from separate +-12v and 5v supplies AND upgrade the on-card regulators with aftermarket discrete units (likely Dexa). I also have a separate add-in I2S-connected DAC coming that I'm expecting to better anything I can achieve with upgrades to the Juli@'s DAC and analog section, but I still think tweaking the Juli@ will be useful as it will offer people an easy-to-implement alternative to outboard DACs (although without the benefit of galvanic isolation between the computer and the rest of the system).

A related point is that the Juli@'s analog outputs are the only component in a cMP2 that uses the -12v supply line from the ATX-24. The Pico-PSU I damaged early in my hybrid/linear experiments only lost it's -12v output, so it still runs my cMP2 EXCEPT the Juli@'s analog output.

Once I've removed the need for a -12v supply (by feeding the Juli@ with it's own supply or only using the Juli@'s digital side and using a separate DAC), I only have to add the 3.3v and 5v portions of the ATX-24 to do a fully linear supply.

I've scanned, but haven't fully digested the implications of the PSU specifications. On first look, a lot of it can be creatively ignored for our purposes. That assumption will need to be tested by building the 3.3v and 5v linear supplies and seeing if they work with a potentially 'sacrificial' motherboard. I'll have to find some inexpensive ones that are similar to the current Gigabyte recommendation... I don't want to destroy a now-hard-to-find Gigabyte board developing this.

After reading the PSU spec, I have a few thoughts... the 5VSB line provides a 5v supply even after the power is switched off for standby purposes, but we don't implement any standby functions in a cMP2 and I strongly suspect that it won't matter if this line is not provided. I do know that using a linear 12v supply that does not follow the PSU spec's turnon sequencing works ok for what we're doing. I would expect a well-constructed linear supply to meet the ripple, regulation, and noise specifications without any issues. The power-on sequencing specs that might be interesting to implement, but they really don't look too bad.

Depending on how other aspects of my life go over the next several months (work is pretty brutal right now), this may be a late-summer project.

In the meantime, the SQ gains I've gotten with the Pico-PSU-based hybrid/linear supplies have been very impressive. I now have better caps (Elna Silmic II) that I can install on my Antec supply and after I put them in (maybe in the next two weeks) I will do another listening comparision between the capacitorized-Antec and my hybrid/linear, but the initial comparisons were not a comparison... the hybrid/linear beat the Antec decisively in all areas. And the linear 'dirty' supplies have provided a nice additional boost. I can strongly recommend both of these to anyone wanting to get the highest SQ currently available out of their cMP2. And they are not dead-ends as the two linear 12v supplies will be retained when adding the 3.3v & 5v supplies

At least one other inmate has done a similar setup and he may be able to add his impressions here too.

As for ripple out of the Pico-PSU, I do have some caps on order to use on the output of the Pico. Of course, that's the parts order that has been the slowest to rrive, but I will report on that once I have them and can install them. BTW cics, where did you see the ripple specs of the Pico... I didn't see them in a quick look-around.

I'll also report on my Juli@ mods over the next few weeks and on my dirty supply comparison trials (to try to determine what supply makes the most SQ difference).

Greg in Mississippi


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  • RE: All supply is now Linear except for Pico PSU - GStew 12:36:06 03/28/09 (0)

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