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Extreme Juli@ Digital Section Mods

BACKGROUND...

I've spent much time over the last few weeks planning and executing some of the extreme JulI@ digital modifications I began outlining above. My direction has gained focus and changed somewhat from above:

1. Improve the power fed to the key processing chips.

2. Reduce EMI & RF interference produced on the card & fed into it from the computer.

3. Improve the signal processing.


SIMPLIFIED DAC...

Before starting this inquiry, I first simplified my downstream processing by replacing my fairly complicated AK4399-based DAC (6 regulators, dual-mono output stages) with a fairly simple one based on the ESS ES9022. This is a very fine, low-cost ($2!) DAC from the same people who created the ES9018 chip used in Twisted Pear's Buffalo DACs and the latest Oppo Blue-Ray players(among others). It is an I2S-input only chip (like the AK4399 and many other modern DACs, but unlike the ES9018) with an onboard output stage. Only a single power supply of +3.3v is used for both the digital processing and the output stage. It uses an onboard charge-pump to create -3.3v to allow its output stage to provide a full 2v level.

With only one voltage feed (most high-end DACs such as the ES9018 and AK4399 have at least one for the digital processing and one for the analog processing, if not more) and very minimal options that can be selected, I thought this was a good way to minimize the variables so I could better hear the impact of the Juli@ mods.

Here are a couple of pictures of my initial implementation of the ES9022 DAC card (provided by EUVL on DIYAudio) mounted on a baseline-modified Juli@ digital section. The Dexa regulators are used as pre-regulators here:








Here is the same card with the Dexas bypassing the on-card monolithic regulators:





BTW, some have suggested that a very good implementation of the ES9022 (and its replacement, the ES9023) will better a merely-good implementation of the ES9018, so I do not feel I am limiting myself by going with this $2 chip. (see the last few posts in this thread: http://www.diyaudio.com/forums/digital-line-level/151846-anybody-using-new-ess-vout-dac-es9022-5.html). It certainly competes with my AK4399-based DAC and with the Dexa regulators bypassing the on-board ones, I'd rank it as slightly better.

THE MODS SO FAR...

Before going on to what I've done so far, you might want to go back to my first post in this thread and revisit what I've done in the past to improve the Juli@ digital sections.

So far on this round, I have worked mostly with my first area of focus, improving the power feeds:

1. Replace my traditional input filtering using 2 1000uf Black Gate Standard capactors with a combination of conductive polymer capactors and high-value ceramic capactors. These capacitors are both designed to work effectively to higher frequencies than the BGs. Also, I installed them in a manner to minimize lead length inductance to preserve their high-frequency capabilities. I did this by installing them at the bypass caps at the input to the 3.3v regulator on the back of the Juli@ digital card. These bypass caps (labeled "BCxxx") are helpfully positioned as close as possible to where they are needed, so they are better mounting points for these add-on caps, especially coupled with very short lead:










2. Move the Dexa regulator I have traditionally mounted on a heatsink about 6"-8" from the Juli@ and mount it directly on top of the 3.3v Dexa on the JulI@ card. This again reduces inductive high-frequency loses, both for the 5v chips on the Juli@ and at the input to the 3.3v Dexa.





3. Feed both the 5v & 3.3v Dexa regulators separately from my 11.5v raw DC source instead of having the 5v Dexa feed the 3.3v one. This provided greater voltage headroom to the 3.3v Dexa, but eliminated the advantage of feeding it from a well-regulated 5v source AND the advantage of the short connection from that source provided in #2 above. To gain some of this back, I added more conductive polymer caps at the input of the 3.3v Dexa.


Pictures coming later!

4. Install additional bypass capacitors at the power input to each of the key chips. While the stock Juli@ is well-designed in that it has the small bypass "BCxxx" capacitor on the back of the Juli@ cards at each of these locations, recent chatter on DIYAudio suggests further gains with higher values.





While I haven't measured the BCxxx caps, I suspect they are between .1uf & 1uf. The caps I added are 100uf. *** Update *** The BCxxx capacitors already on the Juli@ are about .5-.6uf each. ***

Note that I haven't yet installed additional bypasses across BC10, BC11, and BC12. Since they have other components directly next to them, it is much harder to install the caps here and not cause a short. I have practiced on an old Juli@, but plan to wait until I get through most of the other mods to do these just in case I damage the card when I do them


SONICS?

Step 1, replacing the add-on power supply filtering caps provided a very nice improvement in detailing, dynamics, & bass power & definition. Also instrument solidity and texture was improved.

Step 2, provided more of the same, but with the addition of greater instrument separation & layering.

Step 3 was originally disappointing as I did not add more power supply filtering at the input of the 3.3v Dexa. I could hear greater precision, but dynamics and bass took a step backward. Redoing it with the added caps at the 3.3v Dexa input brought back the dynamics & bass and made it an acceptable alternative. Since step 2 & 3 are alternatives, not a direct linear upgrade, I need to go back an forth a couple of times to see if I can identify the differences between them and decide which I prefer. I suspect long-term I will like 3, but I may try an additional Dexa (probably set to 7.5v or so) before the 3.3v one to see if I can get the best of both worlds.

Step 4 added more detailing & separation, but was a smaller improvement than the others so far.

CERAMIC CAPACITORS?

One caution I have on all of these mods so far is my heavy use of ceramic capacitors. I remember Marsh & Jung's Picking Capacitors and how ceramic caps were some of the worse measuring & sounding caps at the time. But I see that several things are different today:

- Back then, audio circuits did not involve much if any digital processing. Today, digital sources are the standard. And building a good digital circuit is different than traditional analog circuits (and this drove the creation of surface mount components, among other techniques). Digital circuits have to be well-behaved in the megahertz to gigahertz ranges. And large, long-leaded teflon, polyprop and polystyrene capacitors just don't work well in these ranges. Making a good digital circuit means doing things a LOT differently than making a good analog circuit.

- Ceramic (and for that matter, electrolytic) capacitors have gotten MUCH better over time. While I wouldn't use the same components in both digital and analog circuits, the small, short or no-leaded ceramic and high-frequency electrolytic caps I'm using here are now good choices and the same components you see in other high-end digital circuits. Also, they are the same type of components already on the Juli@... Just more and better of them.

I did detect a bit of harshness when I first put in any of the ceramic caps... And that has diminished as they have broken-in. With a couple of weeks of time on steps 1 & 2 by the beginning of this previous weekend, the sound was very smooth and not harsh at all. Adding the components I used in steps 3 and especially 4 brought some harshness back, but now a day or two later, smoothness is returning.

WHERE TO NEXT?

My next steps are to continue with improving the power feeds and reducing EMI & RF interference produced by the card. These will include:

5. Remove chips not needed for I2S connectivity... The TOSLINK output, the digital input optocoupler, the SPDIF input/output AK4114, and the SPDIF buffer/selector. I only have a concern about the AK4114 and whether the card will continue to operate with it disabled, so I will try disabling it first on an old, sporatically-functioning Juli@ (one of the first I modified).

6. Reduce RFI & EMI pollution by shield the chips using a stick-on ferrite material and installing ferrites on the power supply lines (Thanks hfavandepas!). I also plan to try conductive foam as a absorber of RFI/EMI, as championed by Elizabeth on the Tweak Asylum.

Then I want to improve the signal processing:

7. Upgrade the on-board clocks using the Fidelity Audio Micro Clock which can be purchased with the two clock frequencies needed for the Juli@. While I don't expect these clocks to equal the higher-priced upscale clocks, I do expect to hear a strong hint of what they can do for the sound.

And finally, complete step 4 by going back & install the additional bypass caps I deferred.


AND BEYOND?

By the time I have gotten to this point, I hope to have information on devices I can use to provide galvanic isolation at the I2S interface.

Then my question will be: Will I be stuck using the Juli@ at the GA-H55M-UD2H level or will the H61 motherboards with the non-native PCI slots work ok for an audio setup using the Juli@?

Greg in Mississippi
Everything matters!


Edits: 11/14/11 11/15/11 11/15/11 12/02/11
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