Valab Dac-First Impressions - Page 100

I sent Kevin (the creator of Valab) the following email and his response is below mine. Based on his advice, I've let it just burn-in, but I have a fan blowing right on it, which is keeping it very cool and it sounds decent. I'm planning on letting it burn in with the fan for a couple more days and then try it without the fan. My suspicion is that once it gets hot, the static will emerge again, but I'll post again after a few more days.

Here is my email to Kevin:
Here is Kevin's response to me:

Well that was quick! I ordered the DAC on Saturday, it arrived in Holland on Friday. Just installed it, and got it running on Linux (had to remove Pulseaudio first). Awesome! Sounds very good so far, can't wait to get back to you after some burn in and testing!

LL1574

Lundahl LL1574 arrived.

Sounded a little closed in at first. After some 60+ minutes some air returned. I was never happy with the vdH coax interconnect. I got what looks like milspec Belden which turns out to be pure threaded silver coaxial. Made an interconnect from it and now the combination is a bit better than the Pulse transformer and vdH carbon type cable.



I am at pains to describe all of why it is better. Theres things like when a drum skin is hit. You now get this sound of the pre-hit. Very delicate detail things like that but less bright than the previous transformer. Softer. More colorful, maybe. I know it is a little more engaging and insightful.

This pulse transformer trick was a nice one waiting in the wings. And I think a silver coax makes a difference.

Does anyone have any suggestions on mods to the DC-30W? If not I think I'm done.

Just got Horowitz's newest never released stuff from the Yale vault. Right after Enrico Rava's ~ New York Days.

Just sent my turntable's bearing assembly out for work and I don't think I will miss using it for a while.


EDIT: After more listening I have to say the Lundahl transformer is more than just a bit better than the previous transformer. For instance the Blind Faith CD was always a mush. That CD has lost most of it's sibilance and is now very involving. The cymbal crashes are still crappy but all the rest is far better. It is very worth going the Lundahl route.

Che Lundahl:

tons of information

This Lundahl transformer is a big big win. There is tons of information being easily served up. Going back to what Bill said about delivering a clean digital signal, about how that would really show what the DAC can do. It's no joke.

I have two pulse transformers that are jump balls. One is the pull from my VALAB the other is new. If you want one gratis, shipping and all, queue up FIFO.

Hi Pat,
Nice to hear that the Lundahl transformer is working very well. There's only one little thing you might have not seen. The LL1574 is a AES/EBU to SP/DIF converter. This means that the incoming signal should have a 110R impedance. You are probably not getting the best out of the transformer as you are feeding it with a 75R SP/DIF signal.
You should actually use the LL1572 when you want an 75R galvanic isolation. I ordered mine to (The LL1572) but it has a delivery time of approx. 4 weeks.

not 100ohm?

I thought I saw a 100ohm resistor on the board where the coax came in. I have to go recheck.

The terminationresistor on board should be 75R for a coaxial sp/dif signal. If they used 100R you should exchange that one for the correct value. Quite important. :-)

I double checked with Lundahl today and we indeed need the LL1572. The LL1574, which you use, is only needed when you want to feed the DAC an AES signal.

ah well

I must have misread the 100ohm or there is another resistor behind dropping it to 75. Which is why I got the transformer with the 110 secondary. Dang. I will just swap back to the other Pulse trans I pulled .... More detail keeps coming on. Can that be the DC-30W?

?

I took a look at the values posted on K&K for all the digital transformers and only one shows a 75ohm outward facing resistance which is the LL1574:

Digital Audio Transformers
Type Impedance Ratio Usage/Comment
LL1572 110 : 110 ohms Digital audio
LL1573 110 : 110 + 110 ohms Digital audio splitting
LL1574 110 : 75 ohms Digital audio AES/EBU : SPDIF interface
LL1593 110 : 110 + 110 + 110 ohms Digital audio splitting

aes/ebu

aes/ebu is the standard format for data recvd and sp/dif is basically the same. differences between the two are impedance and connectors but the DAC will be reading data by way of aes/ebu format. [so far as I am reading now] The resistance is 110ohm for that network. The SP/dif comes in at 75ohms. You can either bang them together or match them with the Lundahl.

using a 75/75ohm transfor give galvanic proection but does not match to the internal aes network. The Lundahl does that extra step up.

All the other Lundahl transformers look like you will have to add a 75ohm resistor to the outerfacing tap since they are all 110ohms.

Now a 75:75ohm will look at the interal resistors set to 110ohms ... which is what it looks to be on the VALAB. Which is why the 1574 is a mathcing transform in this case.

This is a more informed version of my muddy thinking when deciding to buy the LL1574. I will still check that board for what resistors are laying in the path.

Some things where unclear to me too, that's why I contacted Lundahl. Actually the LL1572 handles all impedances with a 110 ohm maximum. The outgoing secondary always needs to be terminated. In our case of the valab this already happens on the board so there's no need to terminate it again.
In case you have the LL1572 and want to go into the Valab with an AES/EBU signal, the only thing you have to do is replace the 75R on the PCB for a 110R resistor to get the correct termination.
In the case of your LL1574 the transformer requires the 110R input and gives you a 75R on the output. I think there mst be an easy solution for this but I have to check that.
If you want to be sure that you have got it at the right end you can contact lundahl. They are very helpful.

things are still unclear

I have the 75ohm tap tied to the RCA and the 110ohm tap going to the PCB.
I do not find a 75 or 110 ohm resistor on the board and I broke both my meters.

If you have a DM can you measure where it says "coax" on the board?

If it reads 110 I can stay with the Luindahl. Well, actually the other transformer is a 110 to 110 so conceivably I am better off with at least 75 ohms at the RCA.

But if the board reads 75ohms I can swap back in my 1:1 @75ohm Pulse transformer.

cap can go

It alos looks like the input hits a .1uF cap which, as I am reading, can be removed if you have caps on the digital out on your transport.

My CDP has a 765ohm transformer so I think I will remove that small cap to see what happens.

I bought the Valab a month ago and after noise from one channel I returned it to Kevin for replacement. I hope everything goes OK, but this thing with Valab is very stressful lottery.

there is a difference

swapped back and forth between the Lundahl LL1574 and the PE-65612 and the Lundahl delivers a warmer weightier denser more present thing. The PE is brighter wider sparklier.

I was going to leave the PE in on the strength that the 75ohms might be the correct load but go tired of it and switched back to the LL.

Whew. What a drill.

rhodes54, You are going to have 110ohms going at the PCB same as the 1574 but then have 110 ohms out to the RCA. Word is that as long as the cable is not too long you will have no problems.

I sent an email to Michael asking what the machine loads at the RCA. Even if he replies with '75ohms' I am keeping the LL1574 because it sounds better than my previous transformer.

2+2=5 as dostoievski says.