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Valab NOS DAC - subjective listening and modifications
Mar 14, 2009 at 7:28 PM Post #46 of 2,013
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Mar 15, 2009 at 5:27 AM Post #49 of 2,013
Quote:

Originally Posted by Bill Allen /img/forum/go_quote.gif

Off to the solder bench to put in the 220uf Blackgate NX. Removing the 8 screws on the front/back, the 3 screws holding down the Dac board & soldering in the new BG took me all of 10 minutes.



I'm a little confused here. Unless its the formula as mentioned in the first page I don't see how replacing a 330uF cap (2009 rev) with a 220uF gave it more oomph. According to the data sheet you linked to these are low impedance caps. Shouldn't be that bad. Ultra low is better but I don't know how much you'll hear. Before I pull the 330uF I would like to be sure I'm going in the right direction.

Appreciate the clarification.
 
Mar 15, 2009 at 4:03 PM Post #50 of 2,013
There is another place that is different from it in the previous version.
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Quote:

Originally Posted by zzodhi /img/forum/go_quote.gif
Just got mine this morning. Opened it up and there's a fuse inside now and they changed the output wire to the RCA jack. Everything else looks the same.


 
Mar 15, 2009 at 4:41 PM Post #52 of 2,013
OK, teradac. Spill. Where? Also I notice these metal can lytics no longer say LG I wonder what series that are?

Thanks tubes. Kevin said its a spike resistor and they went back to the fuse and I shouldn't put a high current fuse in it. I'd rather it not have a fuse but I understand from a manufacturing reliability viewpoint
 
Mar 15, 2009 at 7:46 PM Post #54 of 2,013
Gary-Z

welcome to the Valab mod forum, I didn't know that was you. Thanks for posting the pictures of "newest" 2009 board. Teradac says they changed one other thing. Did they finally get rid of that binding blue power LED?

Getting back to the power delivery issue, now I know you have talent in this field so I am saying this for the other members, peeps and TeraDac.

When you look at the Valab Dac power wise you have to split it two divisions.

1).The larger LM084CT regulator supply's positive voltage "only" to the Dac Chips.

2).The smaller LM317T regulator supply's voltage to the rest of the board. (Chipsets).

The various chipsets use very little current, the lion’s share of current is delivered to the 8 DAC Chips which collectively create the 2.1 output voltage. Remember we have neither op-amps nor tubes to step up the voltage, only a passive resistor and cap in the analog path. This is the beauty and Achilles heel of the Valab Dac.

TeraDac set the input voltage to these chips at 7.8V (Maximum is 8.0V). This is done by the 2 little resistors after the LM084 voltage regulator. The 220uf Cap in question acts a reservoir to supply/limit current to the smaller reservoir 10uf caps sitting directly on each DAC Chip. How large a uf and how fast the recovery of these caps dictate the size of the soundstage and dynamic capability of Valab Dac. Remember these Dac chips were not designed to stack 8 in parallel. Numerous people have tried and failed to make this design viable in the past. Cooling of the Dac chips and proper power delivery being the number one problem. Hats off to TeraDac for making this design a reality.

Given a low jitter input signal to the Dac Chips (no small feat either), changing the voltage or uf value/type of caps in the power supply to the Dac chips changes the way this Dac sounds. So you see this is how you change the voice the Valab DAC.

How do you want yours to sound???
 
Mar 15, 2009 at 8:05 PM Post #55 of 2,013
Hi Bill. Excellent discourse. I haven't studied the schematic so it's helpful to me too. I think the cap on older versions (guessing by the board script) has smaller uF for that cap which they've now gone up to 330uF.

In conclusion you're saying the rule of 5 dictates lowering the 330uF to 220uF and synergistically it will have more reserve. Is that right?

How do I want it to sound. Why the best it can, natural, effortless, grainless presentation that's involving and musical as it is transparent, How's that?
 
Mar 16, 2009 at 2:13 AM Post #57 of 2,013
Has anyone worked with vibration control pads/grommet on the dac board? Pulling it tight with the case doesn't seem the best. Vibration from the trans can still transfer from the connections going to the board.

Also I've been doing a lot of research on the cap replacement. As you all know SMT caps, if they're very good, will yield better results than through hole organic types in this application. Maybe its better and more elegant to find hi-end SMT caps as a replacement for what's there.
 
Mar 16, 2009 at 6:31 AM Post #60 of 2,013
G-Z,
I don't believe it's a matter of 330uf vs. 220uf if you are mixing and matching caps for the Dac chip power delivery. This sort of mix and match cap situation is what limits the stock Valab Dac dynamic's. Here we find three 1000uf Rubycon XYF, then a 330 uf OS-Cap and finally 10uf mica caps on the Dac chips. Better off to use the Rubycon XYF straight though IMO, including the ones on the DAC chips. When using the "same" type of caps ... the rule of 5 would apply.

If you "want it all" pick up the Rubycon Blackgate FK's while they are still available. My Mod Dac already has all the quality's you are searching for. If you forgo the 8 chipset caps, you are looking at:

3ea. 1000uf FK
1ea. 220uf Fk (Maybe give the 470uf a try)
8ea. 47uf Fk

These caps will cost your around $100 with shipping. No guess work, already proven to be outstanding in my Mod Dac.

Then again you could always give your secret caps a try. Rule of 5 still apply's.
 
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