Zero global feedback

The Cube SE is designed to offer low distortion without global feedback. Main feature of the design is that identical MOSFETS are used to cancel non-linearities.

A minimum amount of semiconductors is used to ensure a short signal path. AC coupled circuits offer DC protection.

The absence of global feedback leads to more musicality.

Single ended

The Cube SE is a single ended design.

Single ended designs eliminate cross-over distortion. Unlike push-pull circuits, single ended designs mainly produce even-order harmonics. Even-order harmonics sound natural while even smal amounts of odd-order harmonics sound harsh.

MOSFET

The Cube SE is a simple MOSFET based design.

Lateral MOSFET properties are essential for maintaining musicality. With MOSFETS simple drive circuits can be built, also MOSFETS are self protecting.

Transformer

The Cube SE uses a Toroidal transformer.

These transformers emit minimum magnetic field and produce less interference. We do not use SMPS (switch mode power supplies) as these emit too much interference.

Modular design

The Mosaic UV is based on a modular design.

The layout of each module has been optimised for maximum performance. The modular design enables us to build and easily test the separate modules before plugging them into the mainboard. All pins on the Mosaic UV are gold plated.

DAC module

The Mosaic UV DAC module uses a passive resistor matrix to generate the output signal.

Please note that this is NOT a regular R2R design but uses ternary logic. The matrix design eliminates all issues related to zero crossing.

All the DAC modules use high accuracy resistors, and the lowest level bits are tuned with extra resistors to provide optimal low level performance.

USB module

The Mosaic USB module

I have been developing software for over 30 years and I was convinced that from a digital/software point of view that digital music was just a sequence of bits and if they arrive at the DA converter without error then it is irrelevant how or where the sequence of bits are created. So in my mind using any PC with any playback software that was bit perfect should sound the same. Unfortunately this is not the case and some PC's "sound" better than others and some playback software "sounds" better than others.

If however you look at digital music from an analog/component point of view each "1" or "0" is an analog voltage level on an electronic part. So for a 3.3 V part 0 V on a pin is a "0" and 3.3V is a "1", but what about 0.8V, and 2V or even 1.65V ? A digital world "1" and "0" are implemented in an analog world using ranges of voltages representing "1" or "0".

In a digital world a stream of bits representing music samples is a square wave that switches between logic "0" and logic "1", in an analog world this square wave can be represented as an infinite summation of sinusoidal waves, and square waves contain a wide range of harmonics that can generate EM radiation and interfere with nearby circuits, also square waves are never perfect in a real-world circuits.

It is advised to use sine waves to prevent EM radiation for very sensitive circuits like AD conversion. For DA conversion however I2S square waves are used. Sinus waves are probably unsuited for DA conversion because this will result in timing errors due to range of voltage that is considered a "0" and range of voltage that is considered a "1".

Another very importent point to note is that ideal square waves only contain odd-integer harmonics while real-world signals contain all integer harmonics. When you look as I2S, the standard used for interfacing the stream of bits representing the music samples with the DA conversion, you can see it is a square wave. So it is probably full of EM radiation that will always interfere with the DA conversion circuitry.

For reference also see: https://en.wikipedia.org/wiki/Square_wave


So at some point the digital data has to be handed over to the analog conversion circuitry, this is the most critical point. Here all the accumulated "noise" from EM interference of the operating system, network, music player software and the DAC microcontroller are injected into the DA converters. The part closest to the DA converters (the DAC microcontroller) will probably have the most influence on EM interference injected into the DA converters. We think square waves are unsuitable for handing over digital music samples to the DA converters (accumulated EM interference), and we also think that sinus waves are unsuitable for handing over digital music samples to the DA converters (timing errors).

That is why we had to make our own USB firmware solution to hand over digital music samples to our discrete DA converters. Thus our goal for the USB firmware in our microcontroller was to keep it as quiet and simple as possible.

This eventually resulted in using a single core 32 bit microcontroller running on a single 12 Mhz XTAL. The firmware now uses one single interrupt for the sample frequency, uses hardware counters for timing and uses polling to handle the USB stack. This is only possible in UAC1 where latency of a few milliseconds can be tolerated by the host. It is not possible to create such a quiet and simple UAC2 solution and adhere to the UAC2 timing specs required by the host. Any UAC2 implementation will therefore produce much more EM interference that will be injected directly to the DA converters.

Because our firmware is not using I2S at all we were able to create a simple interface to hand over the samples to the DA converters while minimising the injected EM interference.

Our UBS module is compatible with UAC1 standards and doesn't need any hardware drivers on the host.

Volume control module

Our Mosaic UV DAC modules use a resistor matrix to create the output signal. The volume control module also uses resistors to attenuate the output of DAC modules. A minimum number of relais are used to provide 32 steps with 2 dB attenuation per step.

With these modules the Mosaic UV is completely passive and DC coupled.

The volume setting is controlled by the microcontroller and is available as mixer control in the USB host. Most software and operating systems can control the volume of the Mosaic UV. The volume is also controllable by an optional IR remote control.

Headphone buffer

The headphone buffer in the Mosaic UV is based on the same design as our Cube SE amplifier but then implemented as a buffer (no amplification).

After having completed our Mosaic UV USB DAC, Cube SE amplifier and our No-Box OB speakers we were not satisfied with the sound of our headphone output. From the start we wanted customers to be able to experience the same extremely quiet, incredible musical and very accurate sound through our built-in headphone buffer as through the setup with Mosaic UV, Cube SE and the No-Box OB. The headphone buffer was clearly not on the same level as the Cube SE.

We spend a lot of time and effort to get the Cube SE sound from our headphone buffer. In the end we used the same simple design as our Cube SE with some specific modifications to match the performance of the Cube SE and No-Box OB.

We used a Bayerdynamic DT 990 Pro 250 Ohm dynamic studio headphone as reference.

The headphone buffer on our Mosaic UV is very important because it makes it possible for customers to hear the sound of our Mosaic UV as we experience it through our Mosaic UV + Cube SE + No-Box OB setup when using the Bayerdynamic DT 990 Pro 250 as reference.

You can use our Mosaic UV without amplifier or speaker to enjoy the music using (studio) headphones. But on the other hand it provides a reference to determine if your amplifiers and speakers are capable of producing the same sound.

The headphone buffer in the Mosaic UV is only connected to the internal power supply. To use headphones you plug the variable output of the Mosaic UV into the headphone buffer input on the back of the Mosaic UV. Then you use one of the jack plugs on the front. Often headphones are equipped with 3.5 to 6.35 mm screw-on converters, please use the "native" plug on your headphone without converter.

Our headphone buffer can also be used to directly drive your speakers, although the volume is low you can use it to evaluate the SQ of your amplifier.

Power supply

The power supply of a DAC is of great influence on the final sound quality of the DAC because it is in the signal path. It also has to deliver a stable voltage while being able to respond quickly to load variations.

Like the rest of our designs, the built-in linear power supply is simple by design but has the precise balance needed for our Mosaic UV. The output of the buit-in linear power supply is further optimised by the dual voltage regulator module on the mainboard. This design is the result of years of testing all possible voltage stabilisation principles and it is now equipped with dual capacitance multiplier circuits for the best results.

Mainboard

The mainboard of the Mosaic UV is the backplane where all Mosaic UV modules are plugged into. Output terminals, the USB connector, the LEDs and the push-button are soldered directly to the mainboard. Also the power supply capacitors and pre-regulators are placed on the mainboard.

All Mosaic UV connectors and pins on the modules are gold plated.

Bitperfect test

The Mosaic UV has a built-in bit perfect test.

This means that we can check if all samples from a track actually arrive in the Mosaic UV without modification of the playback software or operating system.

When the track is modified by e.g. equaliser, sample rate conversion or other conversions the specially prepared test track will no longer contain the known sample values.

This can then be easily checked in the Mosaic UV. When the test track is received completely without modification the green bit perfect led will light up.

The led stays on until the stream is stopped.


Below is a graph of a 16 bit 96 kHz test track.


bitperfect


For a 16 bit file the test will start when the Mosaic UV detects the lowest value (-32678 for 16 bit), then the bit perfect routine will check if each next sample is exactly value 1 greater. When this is true for all 65535 steps then and only then the green bit perfect led will light-up. When one of the next steps deviates the bit perfect routine is aborted.


Warning: Turn down the volume otherwise a loud "plop" will be heard !
Don't use muting because then all samples that will be send to the DAC will be zero and bit perfect test will fail.

The 44.1 kHz / 16 bit test takes about 1.5 sec after first negative value.
The 44.1 kHz / 24 bit test takes about 6.3 minutes after first negative value !

The 96 kHz / 16 bit test takes about 0.7 sec after first negative value.
The 96 kHz / 24 bit test takes about 3 minutes after first negative value.


Download bitperfect test tracks

Lights out

The Mosaic UV is provided with a "lights out" function. This allows the Mosaic UV to be configured so that all LEDs on the DAC go out after 10 seconds. Only when there is a user action the LEDs will light up to indicate the new status, but 10 seconds later all LEDs on the DAC will go out again.

This function can be activated in two ways:

  • With the push-button on the back of the Mosaic UV
  • With a key on the optional IR remote control

The selected option whether or not to use the "lights out" function is stored in the Mosaic UV.

When restarting the Mosaic UV the stored option will be used for the "lights out" function.

Mosaic UV + RaspberryPi 3 Model-B

In line with our Less is More approach we created a minimal RaspberryPi image. This image transforms the Mosaic UV that is connected to a USB port on the RaspberryPi into a minimalistic UPnP/DNLA/OpenHome renderer. The Music is stored on a (Synology) NAS and music is streamed over ethernet from NAS to the RaspberryPi. A phone or pad (iOS or Android) can be used through WiFi as the UPnP/DNLA control point. The phone, RaspberryPi and NAS have to be connected on the same subnet (important !) This setup is the cleanest solution to stream music to our Mosaic UV. We advise against using a PC or equivalent device to stream music to our Mosaic UV.

rpi

RaspberryPi 3 Model-B
  • RPI3, 1.2GHz 64-bit quad-core ARMv8 CPU
  • Running Raspian Jessie Lite 2016-11-25 Kernel 4.4
  • WiFi + Bt disabled
  • Only using mpd + upmpdcli (UPnP/Openhome)
  • Average load while streaming 44.1/24 = 0.02% (top)

Music
  • Music stored on NAS
  • Music is delivered to RPI3 from minimServer + minimStreamer (UPnP/DNLA)
  • Music is transcoded to wav to offload RPI3
  • Separate setting required in minimStreamer to support transcoding
  • Tested with Synology DS216e NAS

Network
  • Required wired ethernet network connection from NAS to RPI3
  • Required WiFi router on the same subnet as RPI3 (AP)
  • Pad/Phone must connect to WiFi on the same subnet as RPI3
  • Required good connection quality to WiFi for fast response on Pad/Phone control point

UPnP/DNLA/Openhome Control points
  • Kazoo (Linn) on both iOS and Android both pad and phone
  • Lumin on both iOS and Android both pad and phone
  • FRITZ!App Media on Android both pad and phone
  • Any control point supporting UPnP/DNLA/Openhome

MinimServer and minimStreamer
  • Install minimServer and minimStreamer (http://minimserver.com)
  • Install minimWatch on pc for easy configuration
  • Use minimWatch properties menu to modify configuration
  • In Server tab add your music folder(s) in contentDir fields (+ and - keys)
  • In System tab under stream.transcode fill in:
    alac:wav24;,flac:wav24;
  • Use minimWatch to rescan your music folders
  • Use minimWatch show log to see rescan progress
  • On browser (pad/phone) you also have limited access to MinimServer functions on http port :9790 of the NAS.

Shutdown RPI3
  • Set your RPI3 to receive known ip address in your WiFi router
  • Use an ssh app on your phone/pad and login to the RPI3 using known ip address:
    ssh pi@xxx.xxx.xx.xx with password: raspberry
  • When connected to RPI3 enter:
    sudo shutdown -h
    Then wait until green led on RPI3 quickly blinks 10 times and only red light is on
  • Next time to shutdown you could login to RPI3 and press [up] button + enter to shutdown RPI3

Lights out
  • The RPI3 image is setup to switch all leds off after boot
  • Make sure the Mosaic UV is switched on and is connected to RPI3 before starting the RPI3
  • Download the Mosaic UV image using the button below
  • Unzip image
  • Use ApplePi-Baker on OSX to write RPI3 image to micro sd card (8Gb)
  • Use Win32DiskImager on Windows to write RPI 3B image to micro sd card (8Gb)

RPI3 power supply
  • Use a clean power supply for the RPI3
  • We use the power supply of our iPad air (cleanest output of SMPS that we measured)

QOBUZ + TIDAL STREAMING
  • You can use BubbleUPnP Server to stream from Qobuz and Tidal through your NAS
  • Install instructions here: https://www.bubblesoftapps.com/bubbleupnpserver/#synology_install
  • Configure using port 58050 on your NAS in a browser
  • Don't use any Media Servers through BubbleUPnP, they are already available through MinimServer and will degrade sound quality
  • In the Media Renderers tab check the "Create an OpenHome renderer" and give "Mosaic UV" another name e.g. "Mosaic UV QT", don't check the "Gapless playback" as this might interfere with our Mosaic UV volume control
  • For Kazoo e.g. select this "Mosaic UV QT" room and then you can select Qobuz or Tidal in Kazoo Settings
  • When streaming from NAS music collection select "Mosaic UV" room again, otherwise music is also passed through BubbleUPnP Server and will degrade sound quality
  • Note: we also tried upmpdcli-qobuz and upmpdcli-tidal on the RPI3, this also works but will degrade sound quality even more than using BubbleUPnP Server on NAS. We should minimise the load on RPI3 for best sound quality


Download Mosaic UV image for RPI3