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Valab NOS DAC - subjective listening and modifications

post #1 of 2010
Thread Starter 
Purpose of this thread is to share modifications of the DAC for use with audio equipment vs computer systems. There are known issues PC related and in an effort to separate that so we can concentrate on getting the best we can from this DAC for use in audio systems a new thread was suggested. Audio Systems for our purposes means a CDP/transport putputting via COAX or Toslink to the VALAB NOS DAC then out to [pre]amps and transducers.

2008 and 2009 VALAB DACs welcome.

In a recent email with TeraDac they told me that coupling an outboard 600:600 transformer could be done but the caps would need to stay in place:

"Hi,
Thanks for your long-term support in this thread. ^-^
For a general 600:600 OPT, we are afraid you can not remove the output caps because there is DC in the output. The DC-current will magnetise the core if you don't block it. However, you can tweak the output caps with different capacity for your 600:600 OPT.

Good luck !

TeraDak"

Which means I will push on with putting CineMag trannies in a separate enclosure and use short interconnects and see if there is anything to see.

VALAB sells interconnects with a toroidal tranny ... why not CineMags?

Magic Box Silver Analog Interconnect for 300B 2A3 6DJ8 - eBay (item 290272519462 end time Apr-02-09 20:00:00 PDT)
post #2 of 2010
Hello Pat, I have a question, I'm getting distortion from my PC, Just Kidding!!!

The transformers sound like a good idea but what would be the advantage if the coupling caps stay in place, it's another part in the path.

Bill, you never let us know what you thought of the 220uf cap for the V Reg. I did the same but took it out, in my Teradak the 220uf sounded a little too vivid/sharp.
post #3 of 2010
how bout a step by step guide showing how to install the 330 ohm resistor's so my PC specific problem, that only effects PC's and can't possibly effect other transports can be resolved (despite what the manufactor says). what pc specific problems where you refering to anyways?
post #4 of 2010

Fresh Start

Hey Pat & Phill,

you know with the 220uf regulator cap, my Dac started to clip at 0db ... just kidding, couldn't help myself either!

Seriously I have yet to try it in the Control Dac. This however will be the first Mod on the C-Dac.

Meanwhile my Mod Dac (as described on page 50 of the old forum) is rolling through 500 hours, 300 post Cryo. Sounds absolutely outstanding. A total success.

I will slowly start to Mod the C-Dac and see where the bang for the buck lies. Perhaps for the 220uf on the regulator we will need to place the 8 47uf directly on the Dac chips like in my Mod Dac. I will get 220uf in on Tuesday and report my findings.

Pat I see you are still determined to get that transformer coupling going. I remember nominating you for that job a couple of months ago. A worthwhile adventure in my book.

And so it begins.
post #5 of 2010
...anyone got an extra $300 to try those cables. Sure look interesting, and at the very least a well-made work of art.

Nope, I'm not hi-jacking the thread ...watching with interest the mods you guys are up to and may pull the trigger on this DAC and toss in some V-Caps as recommended by Empirical.

BTW, has anyone tried feeding the Valab 24/96 HDtracks or similar?
post #6 of 2010
Here's a link to the data sheet for the V regulator used in the Valab,
http://www.promelec.ru/pdf/LT1084.pdf take a look at page 6. I was taking a look to try and get an idea of what size caps are needed and man there is a bunch of mumbo jumbo depending on different scenarios. What struck me was in one scenario they recommend using a 150uf electrolytic or a 22uf solid tantalum cap on output of the VReg. I am a little confused by this, why would the cap values be different depending on the use of an electrolytic or tantalaum? If there is some sort of difference between the type of caps does that mean we've been barking up the wrong tree when it comes to output capacitor values. The 2009 dac uses 10uf tantalums, my early production 2008 dac used 47uf phillips caps (electrolytic?). Just wondering if a 50uf electrolytic would be more appropriate for use as coupling caps?
post #7 of 2010
Thread Starter 

CMR

Phill,

Kevin would reply that the Cable/Tranny provides more common mode rejection, thusly lower noise thusly more -more-.

snailmail on it's way, BTW.

Quote:
Originally Posted by tubes View Post
Hello Pat, I have a question, I'm getting distortion from my PC, Just Kidding!!!

The transformers sound like a good idea but what would be the advantage if the coupling caps stay in place, it's another part in the path.

Bill, you never let us know what you thought of the 220uf cap for the V Reg. I did the same but took it out, in my Teradak the 220uf sounded a little too vivid/sharp.
post #8 of 2010
Okay I can post here because my noise is not coming from my computer. It´s there also on the optical and coaxial outputs. Do you here get a sine wave and if so is there any easy way to fix it for someone who can´t solder or anything
post #9 of 2010
Hello Phil, Pat, Bill and others,

I am happy we have this new post to get back to mod and enjoying of this nice little DAC. Hoping to learn more and be brave enough to do some mods when the time comes. Please keep up the great work all!

Regards,

Kenobi
post #10 of 2010
Thanks Pat, I'll put em to good use.
post #11 of 2010
Oqvist. No sine waves here. There's no quick fix for noise that I'm aware of unless it's a damping issue. Some have reported noise during break in that has dissapeared after final break in.
post #12 of 2010
hi guys

there is 3-1000uf caps for power stage filtering could I change to 3 -1500uf caps or should I stick with the stock values.


Rich
post #13 of 2010
Don't know that larger values will make all that much of a difference in a regulated power supply. Better quality caps is another story, maybe others that have made a change can expand on this.
post #14 of 2010
Thread Starter 

the method

There was talk I overheard of about a method of 5.
Meaning 5x is the thing.
If you use 1000uF then 220uF on the Regualor the 47uF on the DACs.
That's one way.

What I did was close. I replaced the stock caps with Rybycon 1000uF low impedance for power filter, 10uF for regulators, then 4.7uF for each DAC.

Focus was the biggest dividend from the effort.

Then I replaced 100uF for all other small electros and it seemed like the clock benefited most.

Output caps were a two step process for me. First I used BG bypassed by non-polar BGs. Nice and weighty. I switched out to .22uF Obbligatos keeping the bottom 4.7uF BG and bypassing the .22uF with a .01uF PIO. A lot more energy and clarity. Way more open.


Quote:
Originally Posted by r8833 View Post
hi guys

there is 3-1000uf caps for power stage filtering could I change to 3 -1500uf caps or should I stick with the stock values.


Rich
post #15 of 2010
thanks,

I had some surplus 1500uf panasonics fm caps that I was gonna try. I will stick with 1000 uf because I have already put in the 220uf at regulator. I changed to rikens at i/v and also changed to 4.7uf mundorf supremes for output cap and is sounds really good so far

Rich
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