Jcat launches the new, 'Femto' USB card

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The Jcat USB Femto is fitted to the current server build. There's a nice lift in clarity and removing grunge using the card, a very worthwhile addition and highly recommended. I did notice a variation in potential of the metal bracket and the 0V of the ATX power supply of about 12mV. Running a small braid from the metal bracket to the case of the ATX power suppl fixed that, now that voltage is <0.001mV.

Using the ATX power at the moment, just wondering if an external 5V is worthwhile considering the ATX supply has (usually) very good regulation and low impedance (it's a 900W unit, came with the case). The 0V is grounded to the incoming ground wire from the AC, but like the metal bracket, other parts like the mobo and SSD were at different potentials, braids to the frame fixed that. I don't have a scope or meter sensitive enough to see if this would affect the output, but the ears like it for sure. Simple to do.

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49 minutes ago, Summit said:

 

ATX power are much better than many here give it credit for. To use a LPS of good quality that are separated from the rest of the computer are beneficial thou, not only because the LPS itself is better but because it prevent all the noise, emi etc from the mother board to pollute the USB card and USB signal.   

The other issue is that are standards for ATX power supplies are built to require them to maintain voltage levels within tolerances, and for values at 5V at high currents or 1.3V, that's not so simple. For the JCAT card, the 5V is not a major problem, since the current demand is small. Wasn't there a problem with the SOtM tX-USBexp that if the 5V external failed, the card would smoke?

From Sotm

"The external power input voltage is +6.5V  +9Vdc, and the input current is 2A max.

While using the external power supply, please connect the internal 4 pin IDE power connector. This is to protect in any case if the external power get fails."

 

 

 

developer-specs-atx2_2.PDF

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On 13/04/2018 at 1:01 AM, jermaink said:

How much PCIe bandwidth can the JCAT cards utilise? Is there any point having it in an x4 slot rather than a x1 slot?

Surely 1x would be plenty enough?

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48 minutes ago, jermaink said:

 

I was thinking in terms of playing DSD256 and DSD512 (I've had intermittent playback issues, which I actually traced to the motherboard).

 

When I was installing the new motherboard, and I was wondering if it was worth actually having the JCAT card in a higher bandwidth slot (if it would even be utilised). If anyone has technical info, that would be great to know.

I follow your reasoning now and would agree. Maybe someone can chime in the mathematics of throughput. Playback of DSD512 is particularly onerous on the CPU(s), so feeding data could be a problem. The player application should offload work to several CPU to ease that burden, HQplayer has techniques for that , not sure of Roon though.

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19 minutes ago, mansr said:

A single PCIe 2.0 (quite old) lane provides 4 Gbps throughput. That's more than 8x the raw bit rate of USB 2.0, which is what DACs typically use. In comparison, stereo DSD512 uses about 45.2 Mbps. PCIe bandwidth is not an issue here.

That settles that, thank you! Means I can leave the JCAT card in the 1x lane.

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2 hours ago, Nenon said:

 

I can confirm that too as I am listening to a computer I just built for a friend of mine. Switching from the JCAT to any of the motherboard USB ports collapses the entire sound stage, makes the sound flatter and harsher, the bass becomes boomier with less accuracy. Also, some motherboard USB ports sound better than other, but the JCAT USB output is way better. 

The good thing is if one wants to hear what 'jitter' sounds like in digital audio, the switching between the JCAT USB output and the motherboard USB makes it really easy to hear :). 

Which goes to prove that using 'raw' USB from a desktop/server/laptop should not be used. Although I don't use the Femto USB board everyday now, it was a no brainer to install the JCAT net Femto for Ethernet with similar results.