Tubulus Concentus I2S cable and DS Mk2

I just received a Tubulus Concentus I2S cable and hooked it up between my PST and DS Mk2. I did get screws with thinner heads for the I2S connectors on the back of the Mk2, as discussed in other threads.

The DAC is showing the red light even though music is playing. I have read that this issue can arise when using non-PSA components, so I was surprised when it happened when playing from the PST (playing from a USB stick not a disc, if that makes a difference).

Have other Tubulus users gotten a green light? My local hardware store had pan head screws, not real wafer screws; they are certainly thinner the original screws and the cable seats more firmly. Maybe I have to order true wafer screws? But if others using this cable get the red light also, then it’s not a problem with the connection.

I’ll post my observations about SQ after the cable has a chance to break in.

Glad you got it to work, looking forward to the results.

The connection light situation is a bit odd in my case (posted this elsewhere but no response). I’m running PST to DS Mk2 via Dragon48 and get a green light on I2S 1 but a red light on I2S 2. This is playing via disc. On hybrid SACDs both layers play correctly (according to the display screen) on both inputs. Hard to say what is going on.


Same for me. I recently switched to a I2S Tubulus Concentus cable from PST to the I2S-1 input of the DS Mk2 and the light on the DS mk2 remains red.
I suspect the DS Mk2 UI is not fully cooked yet, they probably fix this with future updates.

Thanks to both of you for the replies. @jerryd6, I’d say it’s more than “a bit” weird that you get different behavior between the two I2S inputs, using the same cable (and a very high end cable at that, recommended by PS Audio). @2muchgear, your experience reassures me that there is probably nothing wrong with my cable or its connection to the DS MK2. It will be interesting to see what happens with the next UI release. FWIW, I am using the I2S-2 input.

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I updated to the new 2.5.0 FW and the tubulus still shows a red light. I tried 2 other HDMI cables plugged in the same input ( a neotech and an AQ Vodka) and they do lit green so it is only happening with the tubulus cable for me.

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The Purist Audio Design HDMI cable that I used before the Tubulus arrived also got a green light with the MK2. I’ll try the firmware update tomorrow but will probably get the same results as you do. The Tubulus cable sure sounds good, though.

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When you replaced these screws was there any movement in the I2s input that made it difficult to install the new lower profile screw as in moving around so it made it difficult to “aim” the new screw?

Not as far as I could tell. I inserted the new screws carefully and gently, because I realized that it might be possible to push the connector away (further into the DAC); the goal is to have the screw threads pull the connector towards the back panel. Seemed to work OK for me.

Thanks exactly what I was asking. The back and forth and to and fro movement both making hard to impossible to get the thread to align and grab, I do not want to have to open the beast by pulling the cover which is cool looking but a super pain. Were these in fact the M3 0.5 X 6mm that I read were correct here in the forum that you used? Thanks again magistar!

Yes, the size is correct.

Thanks, I’ll pop them in.

Would it work to just replace one screw at a time so the input is held in place?

I assumed that the two I2S inputs were separate (i.e., two different small connectors vs one larger connector with two plugs); but I don’t know that. Somewhere on this forum there are pictures of the interior of the Mk2, which might show this. In any case I did one at a time.

The Tubulus is not an HDMI cable, but an I2S cable using HDMI connectors (similarly as there are I2S cables using RJ45 connectors).

So, what‘s the difference? In order to transfer I2S over a cable, you need 12 lines, which are soldered to pins 1 to 12 of the HDMI connector (so far at least vendors agree upon). This leaves pins 13 to 19 of the HDMI connector for other purposes. Some vendors use these for additional „convenience“. This is where all agreement ends. PS audio seems to use one of them to communicate the preemphasis bit (pin 15?) from the DMP to their DAC. Other vendors may use them differently.

This leads to all sorts of dilemma. As an owner of matching devices of the same vendor, you might want to use a real HDMI cable, i.e. one that connects all pins of the HDMI connector, such that you get the full functionality out of your gear. However, such a cable might not be optimized for I2S and audio. In order to switch to an I2S cable, you actually need to find out which pins your source and DAC combination relies on, and then check with the vendor of the cable, or order it according to your specification (which Tubulus offers). Alternatively, you can rely on trial and error.

If you combine devices of different vendors, it might actually be of advantage to have a real I2S cable, omitting the connection of all or some of the non-I2S pins. This way you incompatibilities between different vendors. For such an example you might want to look at
Holo Red impressions. You might see what kind of dilemma cable manufacturers are in.

Regarding the Mk2, the sound quality should not be affected, unless you want to play some of the very few CDs that featured the infamous preemphasis. You might however miss some convenience, like green light instead of a red.

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You’re right, I didn’t look carefully. Somehow I got the idea that each I2S input had two screws instead of one.

It appears the inputs are attached to the PCB so they are lightly holding on as you change the exterior screws to the flatter ones that accommodate the fatter cable ends.

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@jens42 , thank you. I had picked up some of this information from other threads, but you put it all together and laid it out clearly. Very helpful!

Update: I emailed Tubulus about the red light issue and received a nice reply. They are aware of it and it is indeed caused by pin 19 not being connected. They are working on a cable update to address this. It will be released in “coming months.” So don’t hold your breath, but it’s good to know they are on the case.


Ugh. So what does that mean for current owners? SOL?

Learn to live with that red light. :sunglasses:

I’ve now been using the Tubulus long enough to have a handle on its SQ. I was using a Purist Audio Design I2S cable ($300), which is good – very listenable, with decent details, slightly on the warm/analog side (which I like). The Tubulus is a step up in many ways: most significantly in natural, lifelike sound of instruments and voices; also in detail, instrumental separation, black background, and soundstaging. Not a gigantic leap upward, but clearly an improvement.

I think the Tubulus offers very good value in a mid-price cable. It’s possible that the high-end AudioQuest I2S cables are better, but I’m in no position to buy one now, and I certainly can enjoy my system with the Tubulus while I sort out the whole streamer issue.