Digital Drive

Posted by Claude G (A) on August 12, 2002 at 13:50:50

Hi everybody,

I would like to go back to my last tweak first (filter removal). I noticed then a very very light tendency to brightness, a little too much transparency (or resonance?) at some frequencies around 5kHz. Well, it is mostly gone. It now depends very much on the CD record I play (so might well be just more transparency only), and is much less then before. Is it so because I got used to my new sound now?? Maybe. But, I believe this is mostly due to run in / stabilization of the unit!

When I did this tweak, I unplugged my unit (otherwise on power everyday since 6 months, even when I am on holidays) for less then an hour, and plugged it back again to perform my listening comparisons just after a 30 min stabilization (and then 2 hours test). That was apparently not enough and the ART really needs to suck on the main for over a day to give its best. Indeed, the next morning it seemed the sound was now well in place without any minor comments at whatever frequency…

So, ART tweakers, A/B comparisons are fine, but wait for a day until you write your final comments, even on apparently minor tweaks…

So did I for the…

CAPS BYPASSING (+ 4)

I won’t comment the how and why again. However, I had to change plans as the place inside the ART is extremely cramped, and I couldn’t manage to fit my beloved parts under the main board… as I couldn’t then close the unit! But I didn’t want to swap them for average but smaller parts.

Therefore, I decided to reevaluate and concentrate on the most important, adding caps in parallel (better then a single big cap, easier to do) a little bit everywhere inside the unit where place allowed (please don’t ask me where and how!), connecting the supplementary caps with wires to the board. Caution : this is a tweak for advanced! My ART looks like a mess with plenty wires and Blu tack…

As I am not completely stupid, and in order not to ruin the benefits of additional part, I spent over 5 hours thinking on the implementation. All wires are now between 4 and 7 cm long, so a still acceptable distance, and are quality Kimber (untwisted) cables for amplifier inner wiring. Not that I am too rich, it is just that I had them here, that they are surely good for this application, and that solid core of acceptable section wasn’t simply flexible enough to allow short distances. Also, the small bypass caps are not too small in value, and are as close as possible to the ideal position. Of course, I avoided placing the additional parts near noise / electromagnetic sources, or already grilling parts!

Priority was on :
- C44 and C36, filtering/buffer caps for the + and – op amp’s supply. I decided for each to add a supplementary cap of 100mF/16V (to increase the overall value to 122mF), and to bypass with a 0,47mF cap.
- C19, filtering/buffer cap for the +5V digital supply. I decided to add a supplementary cap of 470mF/6.3V (total is now well over 500mF), and to bypass with a 0,47mF cap.
- C9 and C7, filtering/buffer caps before the + and – voltage regulators. I added for each a supplementary cap of 330mF/25V (to increase the overall value to 800mF), and bypassed with a 0,47mF cap.
- C3 (could have been C4, doesn’t matter, as both are in parallel), filtering/buffer cap before the +5V voltage regulator. The overall value of 2x 2200mF looks fine to me, but requests a step bypass. I used therefore a 100mF/16V cap, and a 0,47mF cap.
- All the resting caps are then not really relevant once this tweaks done

The caps I used where (average) Nichigon Audio for the 470mF and 330mF caps, small SMD caps referenced 17S for the 100mF/16V caps (apparently good), and my beloved silver Siemens MKH (MKTs in fact) as 0,47mF/100V caps.

So, how are things some 12 caps later!?

Well, I have to say that the ART needs a day on the main to be fine after a tweak, and, that caps need even more time to run in (a week at least). So these are first comments, done 5 hours after the implementation.

After the first 30 minutes (I couldn’t help listening a bit), you could immediately notice a step in dynamics, an extension of the bandwidth in bass and highs, and the slight harshness was entirely gone. Noise was further back, and energy everywhere, filling the room, middles were again with an incredible body. Everything appeared cleaned. All in all not a world, but clearly a step further.

However, I was a bit disappointed. The sound was more precise and much more mature, but not really more involving, it was just as musical as before despite the good points, a trade off of some seriousness in the more stable sonic representation. The fun factor didn’t increase after all. Some of the air seemed gone, but wasn’t really : it was just put back in a balance with the bass, making music feel deeper with more kick, but also heavier. So a better result indeed, a further step but was it worth the hassle, as the previous sound was already outstanding?

I left the ART running for 4 further hours, and listen again. And see, +4 are now here! The sound has opened again! None of the dynamics is lost, but everything is now well integrated, and all frequencies are sharp, notes are floating in the air, incredibly light, but this time as well the deepest notes as the down middles, like the treble already used to before this tweak. But the most noticeable step was that I could now hear sounds I had difficulties to identify, and even hear instruments and effects I never had noticed (even on Morcheeba!)

The musicality is top, the sonic stage is even more bolted and extended, while even more dense (but very understandable and realistic), the timing and drive are outstanding, the fun factor at maximum… on whatever record. I wonder if it’s going to improve further?

So, it was worth the hassle, but it is not a mandatory tweak, as the ART was already a world beater, and as I guess most users will reach the limit of their system first, the record quality of most CDs anyway! +4 is good, especially from where we stared from, but is also a bit shy for a 12 parts strategically very important cap tuning.

Does it mean my realization was average (wires, caps used)? I don’t think so : the result are similar to those I obtained on other units. It is just that we are reaching the limits of the PS, or even the limits of the entire unit, including DAC chip and CD standard maybe. I guess there is no real limiting factor left now in my ART, no bottle neck, and that every hypothetical further gain will be difficult to obtain, at a risk, trade off, and a certain cost/ pain. After all, it makes sense, as the French ART is sounding like no other DAC before IMHO : it played yesterday Electrocompaniet’s latest upsampling DAC, the ECD 1 (with 24/192 converters, but used as 24/96 in reality inside), completely on the wall, making even its supposed remarkable treble sound nearly unlistenable in comparison. An enormous difference.

I said there was no further bottle neck IMHO (but would be glad someone proves me I am wrong!), so I won’t open my unit again I guess. Taking everything apart, or going for an entirely new external PS (as example), for maybe a further +1 or +2 improvement… And that would mean we only achieved this time 66% of the achievable PS improvements. I believe the current +4 are rather 80% of it, especially as the AD825s don’t seem extremely sensitive to that (good current noise rejection?).

Another explanation could be we reached only the Voltage Regulator’s limits (I admit I do not believe it really). But it is an area to investigate, maybe the last one, and I hope Carlos will soon bring us the answer on that point, even if I am not keen on desoldering the existing VRs on this double sided board, or opening the now extremely cramped unit again (if it ain’t broken…). But, he managed it already once (thanks again), so never say never again.

I hope this helps a bit,

Enjoy Music

Claude G

PS : please, if requested, send comments/questions to my direct mail : claude.gonzales@gmx.net