[English] Test of the SPEC RMP-UB1, the Diretta USB Bridge from SPEC 1

Since december 2020 and the first test of the Diretta protocol, this solution of ethernet bandwidth management between a server and a dedicated PC (named « Target ») link to a USB DAC, finally never left home and remained as my main source. You can read in english the article on Diretta here and 2 other articles describing what you need and how to setup Diretta (français and anglais).

Diretta designers communicate on the low requirements of the “target” whatever we are about memory (RAM) and load of the different processes. They are indicating that small PC like LattePanda or Rasberry Pi are enough to enjoy the performance. I ran few tests with a LattePanda, and one of the conclusion is that paying attention to a LattePanda power supply brings additional sound quality to the sound (deep, impact,..). In my personnal case, the “target” is probably over-designed compared to Diretta recommendation, but, adding high level component like a JCAT USB XE and Netcard Femto PCIe boards drives the restitution to highest levels in terms of aeration and fluidity. It is important to keep in mind the level of prices between this optimized “target” and a Lattepanda.

Motherboard Asus P10S-i

CPU Xeon E1260L

Passive cooling in a HDPlex H3v2 case and ATX HDPLEX 400W LPSU


JCAT Netcard Femto

Diretta is built around an software solution embedded in a USB key for the target (Linux OS, very light) and on an ASIO driver on the “host”. But Diretta is not only a software solution and its business model is also to go to support OEM with modules like the LUCIA one. This LUCIA solution is visible here. For this reason, well known brands start to have a look to such solution and SPEC Corporation seems to be the first one proposing 2 products known as “Diretta USB Bridge” :

RMP-USB1 Ethernet & SFP

The difference in the 2 products is only through their network connectivity : in one case it is an ethernet (RJ45) input and in the other a SFP connector. The tested model is the one with the ethernet input. SPEC integrated in a case, with the same design as the rest of the brand, a LUCIA module with a proprietary power supply and customized USB inputs that are supporting a visual effect through different color to indicate the state of the product at the logo level (red : start, Orange : USB DAC recognized, green : device playing). Concerning the power supply, while this is a high impacting part of the product in terms of performance, few information are available. You can have few more in the following link : Stereosound.co.jp

High-quality analog power supply utilizing know-how as an audio maker Sound using large-capacity analog power supply and high-quality sound parts Realized making. A mica capacitor and an electrolytic capacitor are used to obtain a transparent sound.

Interesting to note that Mica Capacitors are part of the SPEC brand and you could find more information here.

Inside RMP-UB1

To conclude on the connectivity, like Ypsilon and its Phaethon, the power switch is nicely placed below the device, close to the front plate and easy access. The RMP-UB1 with ethernet connectivity is presenting the following inputs/outputs :

  • USB-A port supporting a wifi dongle connection. Still need to understand the interest…
  • un USB-B to enhance the device to a “host” fucntion. This functionnality is supposed to be release during 2021 spring.
  • 2 USB-A outputs to be connected to a USB DAC.

The RMP-UB1 SFP has not any input for the wifi Dongle.

The design made of wood and aluminium is superbe and the chassis is shared with the amplifier RSA-888DT of he brand.

While we have finishing the introduction round, it is time to plug the product. In my case it is quite straightforward as the system was setup for Diretta. Just need to adjust the ASIO parameters in the ASIO driver configuration on the “host” (see below)

Once the power switch is on, only few seconds are requested for the logo on the front plate to move from red to orange and ready to play as the DAC is recognized. The device is recognized very quickly and much more stable than my previous “target” which sometimes, needs a reboot.

In my case; tests have been realized with Roon. While music is playing, the logo is turning to green indicating that everything is running fine. Even if this functionnality is not a “killing one” it is good to have it and…it is very nice.

First thing, the burn-in has been long. The device was 100% new. Stabilization appeared after 7 days and fully stabilized after 10 days (24/24 burn-in). It reminds me the behaviour of some BelCanto products like the RefStream and it is switching power supply not supporting to be unplugged. Need nearly 48hours in order to have this product singing as before the powering down. Difficult to say if it comes from the Lucia or the power supply, not a big deal but good to keep in mind if you are going to test a fresh new product.

Below, you would find the tracks which supported the test.

What is striking first, when the product is stabilized, is the high level of details and well defined stages. It is strongly audible on the “Silent Way” of Wolfgang Haffner. It is very easy to follow the different plays of the different instruments, the dynamic of the piano are bringing a lot of majesty in the restitution. Moving to the live version of “Fragile” of Nils Landgren & Michael Wollny, cover of Sting title, aeration and 3D effect are the most impacting criterias. The voice is fulled and unknown playing instruments in the back is bringing an hypnotic effect, driving us more and more deep in the title.

“Day one” of the movie Interstellar is also a very bewitching title according to the increasing intensity all along the track, with the orchestration appearing step by step. The 3D effect is enveloping the restitution. Pushing a bit more the volume on this quite high dynamic range title, the SPEC RMP-UB1 is doing better than my bodybuilded “target” PC with its JCAT boards powered in 5V by an Uptone JS2 Linear Power Supply( LPSU).

Let’s close by Lambchop that a neighbour and vinyl expert brought to my knowledge few weeks ago. Beyond the discovery, the album “is a woman” is tremendous in terms of emotion, simple and true. I listened to this title with this friend on a LP and his AMG Viella turntable. In this case, what is striking is the weigh of the voice and its impact. Back home, i jump into Qobuz to discover the digital version and launch on my Bodybuilded “target” PC the title “The Daily Growl” . I can not find this impact, probably to the analog version previously listened. Few days after, i launch the comparison with the SPEC, and this famous impact is back. Still perhaps a bit of gap with the analog version but to be franck..not so much.

In a summary, and compared to the bodybuilded “target” PC, this SPEC RMP-UB1 is clearly a success according how simple it is to put in place, it is stable, wonderfully built and bringing tremendous sound performance. What is really fun with this device, is that the impact of the different parameters of the ASIO driver (see this article) is much more audible than with the optimized “target”. I use to listen music with Audirvana or Roon and between the “preset profiles” named “Sync” and “Sync-low” (sync-low is usually used with HQPlayer as with “sync” the CPU workload is too much when transcoding to DS128). With the SPEC, i finally come back to to the “sync” profile with latency to “prefer” and a buffer close to 4. In this configuration, the SPEC is bringing much more than my bodybuilded “target” PC in terms of details, aeration and opening. The association Diretta and SPEC is, without any debate, un success which open to other questions like the quality of the SPEC power supply : would it be possible to go further in terms of PSU ? What about the functionnalities “HOST” mentioned in the manual ? Still some miles to do to close this topic.

Un big thanks of French distributor of SPEC, Patrice ALAPETITE from Next Audio (Facebook). Thanks also a lot to Piet De Vries, the dutch distributor of SPEC for the long discussions, support and the Diretta follow-up on the Diretta Users facebook page. Piet De Vries AudioTweaks.nl (Facebook)

Let’s continue the discussion on the forum here.

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