Valab NOS DAC - subjective listening and modifications - Page 112

Received my Valab (basic) just after Christmas.
Straight away it was better than my MkII Dacmagic, which seemed too forward in the mid-ranges.
It went through some strange phases before it was properly run in - losing bass and then getting it back.
Anyway, this thread inspired me to pick up a solding iron and start moding for the first time (to the extent that the tip on my cheap iron was very thick, so I filed that down using an angle grinder .
Received 2 x .47 Mundorf Supremes in the post today.
Did I tell myself to try out my solding skills on some old boards first? Yes I did.
Did I actually do this? Of course not, I'm a bloke.
The soldering may not be the best in the world, but it's been plugged in and
the music is sounding much better straight away. Better seperation and better
bass kick.
Only thing is, I think I'm losing some off the high end. Any suggestions for this? I assume shoving in some 0.001ufs might help.
For a non-audio/electronic background, it still seems weird to me who the caps can actually change the sound coming out of the speakers!
Anyway - thanks to the many contributors to this thread and to anyone thinking of trying to mod for the first time - have ago.
BG

Bad-Gerbil, If you used the 0.47uf caps for coupling, output caps... then this is prob to low, you would lose a lot of bass. Strange then your reporting the opposite,... losing out in the highs? Pic?

I put an alligator clip lead across the output cap on the right channel of my V2.5 valab dac. Since my preamp has an input cap inline, I felt it would work. Luckily, it does work and nicely too, more details, clarity, and tighter bass. The other channel sounds mushy in comparison. I Got my 340R tx2575 resistors ready to install as well. I will take the thing to an expert to do the actual soldering. Gonna bypass everything after the I/V resistors, just a wire to the rca's.

This may be a crazy idea, but what would happen if i put 130 or 140 or 150 volts into the stock valab instead of 110?

I have attached a picture from earlier in the thread. Just below the output caps there is a black ferrite. Just below the black ferrites are what I think (and measure) is a 25 ohm resistor. They are green. If you look at some older versions that resistor is not there - it is replaced with another ferrite. That green resistor is connected directly to the IV resistor on 1 side. The other side goes to the ferrite & small surface mount cap to ground. (this is the output filter we do not want). It also goes directly to the Output Cap.

The Output Cap then goes through a 47K resistor to ground. I figure I want to get rid of that 47k resistor also?

My plan is to disconnect the end of the 25 ohm resistor that connects directly to the IV resistor. Doing this will remove the 25 ohm resistor, the ferrite bead and cap, AND the Output cap and 47K ohm resitor from the circuit.

Now I will take my new output cap and connect one end to the IV resistor and the other end directly to ground. (My star ground point)

Sound ok???

Thanks again!

I'd definitely NOT connect the output cap between the I/V resistor and ground....an eery silence will be yours.....

the coupling cap should go between the I/V resistor "live"and the 'live' center pin of the RCA connector, the 'cold' end of the I/V resistor should be connected to your star ground.

You will indeed want to get rid of the 47 k output resistor.

Putting 150V on a 110 V AC piece of equipment may result in smoke signals or dealy silence due to KIA voltage regulators as the secondary voltage will be increased to 12V in case you are using the blue wire but to 16Volts if you are using the yellow wire (highly recommended mod). I did not check the specs of the regulators but it may just be too much, in any case using a bigger & better transformer capable of delivering more currrent would be a better approach if you are looking to improve SQ

Thanks for that Marcelnl, OK the Ouput cap gets connected to the RCA plug! duh...

Back to my original question - in original setup all the current that goes through the coupling cap ALSO goes through this 25 ohm resistor, that is why I was a bit concerned about it.

Not sure what this "yellow wire" mod is. ??

aahhh, that may be from the chameleon thread....
the deluxe version (well any PSU with the R Core transformer) has two secondary windings of which the blue has 9 Volts AC and a blue wire has 12V AC.
With 16 DAC chips the power supplied by the blue wire is barely enough and the the blue wire supplies 12V leaving a bit more grunt for the supply.
(Not sure whether the yellow wire is capable of supplying more current than the blue one...)

Folks did connect the yellow wire on the Chameleon and clearly heard SQ improvements
I connected the yellow wire and also had some improvement.

using the normal 9 volt secondary wire should leave enough room to use a higher line voltage ...only question is why and how would you do that, and the point of using a transformer capable of more current is still appbiccable.

i am sorry i meant to say the stock valab nos dac, version 2.5 without the 30 watt power supply,

jeez, I need a digital microscope to see these tiny wires......solder by feel worked I managed to do the Dir mod , and I must say that it sure hits the spot !! (well I cheated by taking digital pictures and blowing them up on the computer to see whether I managed to unsolder properly, afraid as I was of connecting +3.3 V to ground)

more air, soundstage is wider & deeper, more calm in the music and better detail, this mod sure is worth wile although a big magnifying glass sure is to be recommended for executing this one...

On my V3 board I find it very hard to distinguish the printed circuit....and on this board the 3.3 V reg is on its belly with the Dac chips

Some distance needs to be travelled, detail in the low end is very good but the top end is lacking in comparison to what I was used to. Brilliance, space around instruments and absolute definition is somewhat less than what I was used to but this is with the stock coupling cap and the digital input unmodified.

Skibum : I'm now also quite sure that the 25 Ohm resistor you're referring to is in fact a 1 mH coil, on the V3 board there is one connecting the Dac sub board too(color code brown black red silver).

Replaced my 3A Schottky's with Hexfreds. The Hexfreds sound better. I felt the Schottky's were a downgrade from the originals. The Hexfreds are an upgrade.

Replaced my mk132's with Texas Components. Very nice, sophisticated, worth the money.

I'm about done polishing this one.

can someone help me out here pls? I must indeed have popped an eye out as I seem to have trouble finding the info (well it is caerfully hidden in some 100 postings). I'm considering taking out the input caps but can not find whether that is possible without adding the input tranny?

Already added Mundorf silver/gold/oil 1uF input caps to my 'power' amp (all 0,8 Watts) so I can get rid of the output cap :-)

BTW: I am looking at some surgical magnifying glasses to enable me to see what I am doing, why don't they make a discrete version without all that smd stuff for us .....

Wow~ just wow you get a gold freaking star. I wish I had known what the hell i was doing when I read this post. I thought you where mistaken and it was a 1MH resistor. That was before I even knew what the hell an inductor was. I feel like a freakin idiot. I removed one of the Green 1MH inductors from the filter network, after trying to find some at the local radio shack (they don't sell them) and put it in place between the Dac and Main PCB, where I had previously put a 1MH Resistor and bam, everything works like new again. Talk about learning something the hard way, countless hours spent trying to fix this problem, and all it was is a 5 cent inductor!

Valab 3.0 Fixed!

Edit: i tried bridging the dac board and pcb with a piece of silver wire, and it did not work either, that inductor is required there. It can't take much stress either, I broke mine in half pretty easily.

Way to go Wood !

yo guys, I just replaced the RCAs and rewired with soft 5N silver clad in teflon/air (custom made pushed -not pulled- wire from the good old days) bypassing the output caps connecting straight to the I/V resistor.
Also cut off out the digital input selector switch (I never will use optical) and I replaced the 0.01 input cap (for the time being) with an 0.01 wonder cap I had lying around.

I must say the effect is on par with the DIR mod, WOW !
The sound stage widened but most importantly deepened, the black is blacker, and individual instruments loosen themselves from the sound. The top end is now present and I hope it will be as silvery liquidy as with my 1541 plus custom Tube output once the TX 2575s come, but it sure sounds promising already.
Not a hint of harshness, some more detail in the high would be nice though.

Everything obviously will have to settle/burn in, but very promising indeed!

Nice one Mike!!

Oh that low pass filter is a nightmare, what were they thinking? Glad your getting mojo out of that girl now marcelnl. I think the TX's will go a long way to give you more detail.