Musiland 03 US

Musiland has introduced a new version of their MONITOR series of USB audio interfaces. The Monitor 03 US will be available in July and incorporates a series of advancements as summarized in the table below.

You can see from the photo the I2S lines (they are on the same pins as before). Like before, easy to tap to feed a higher-end external DAC. Is it worth it to get the new 03 US for modding? Possibly if you also plan to use the DAC and headphone sections are the enhancement are mostly in those areas.

Enhancements in the USB/FPGA sections are small and perhaps not worthwhile to pay 3X the price of a Monitor MINI

Comparison with 02US

Feature	02US	03US	Comparison
USB Interface	CY7C68013A-56PVXC	CY7C68013A- 56LTXC	Same device, different packaging SSOP vs QFN. Still USB2 speeds since CY is just barely releasing the USB3 version of the device
Clock	24 Mhz Crystal	24 MHz CTS-CB3 Oscillator	Phase Jitter (12kHz-20MHz): < 1 ps RMS. Functionally it is the same as before, it provides the reference clock for the CY USB chip which then feeds the FPGA. Using an oscillator will likely result in lower overall jitter.The clock in my device is a 50ppm, 3.3V part
FPGA	XC3A50A	XC3S200A	The larger FPGA has 4 DCMs that can be dedicated to generate the 44.1 and 48K family of sample rates. Rather than reloading the multipliers every time there is a change in sample frequency family, they can be loaded at all times enabling fast switching of sample frequency [How the clocks are generated]. Thus there is no “fast” and “precision” Sample Rate Control modes in the Musiland control panel
DAC	PCM1793	PCM1798	Dynamic Range: 113 dB vs 123 dB THD+N: 0.001% vs 0.0005%The PCM1798 is capable of supporting 384Khz sample rate even if not specified in the data sheet. Thus 384Khz SR is supported without resampling all the way up to the DAC
I/V	OP275	MC33079	Noise: 6 nV/√Hz vs 4.5 nV/ Hz Distortion: 0.0006% vs 0.002% Slew Rate: 22 V/µs vs 7.0 V/µs Bandwidth: 9 MHz vs 16 MHz Perhaps the weak link of the entire design? MC33079 is not a well known “audio” device (say as compared to the OPA 4134). See section below for Musiland’s point of view
Head Amp	None	TPA6120	03 has a high performance headphone amp: SNR: 120 dB; THD+N: 0.00014%. This is also used in other “high-end” designs
Output	Toslink, Coax	Toslink, MULINK	Mulink is a Musiland proprietary interface for 32 bit transfer and beyond. It is here to connect to their DACs and future technologies
USB Interface	USB2	USB3	03 has a USB3 connector, leveraging the higher power of USB3 (900mA vs 500 mA). The interface speed is still USB2 because of the CY chip used.
Power	Mains DC-DC supply	USB DC-DC supply	According to Musiland, “new technology” has been developed for DC-DC step-uo, step-down and regulation in order to all the electronics to >90% of their performance from USB power. The first implementation of this technology is the Musiland 03 US
Other	–	EEPROM	There is an I2C EEPROM chip on the backside of the board
Street Price	$125	$160	Already available at TaoBao for about 200 RMBs more than the Musiland 02US. Also available from Tam Audio
More Photos	Soomal	Soomal	Overall, you can see an advancement of manufacturing technology with the use of finer-featured devices

About the choice of opamp

As shown  in the table, every component in this new device is “top notch” and well known in the audio circles, except of the opamp.

The new opamp used for I/V conversion has lower noise, but higher distortion as compared to the previous device and especially compared to popular opamps such as the OPA4134.

In addition, the slew rate is also lower: 7 V/us vs 20V/us. Should this be a “concern”? As explained here, even 7 V/us is an overkill for up to 20KHz audio content:

SLEW RATE: Despite what you may have heard or read you only need 0.2 V/uS slew rate per volt of RMS output to perfectly reproduce any signal you’ll ever find on a CD. That number has been verified by several well respected audio engineers like Douglas Self. And it’s conservative–It assumes a worst case full output at 20 Khz which pretty much never happens anywhere but on a test bench. The E7 has about 1.8 volts maximum output, so it needs 0.36 V/uS for the absolute worst case.

Here is another observation from the same blog:

…Any op amp with a slew rate of 3 V/uS or greater is fast enough for nearly any audio application on the planet. And op amps like the 5532 can easily have bandwidths out to 200+ Khz in most applications which results in negligible phase shift or “delays” in the audio band.

Update 7/1/11:

I asked the question of opmap choice at the Musiland forums. This is the answer I got:

Why not use OPA4134 instead of MC33079?
It seems every component is top class for audio except MC33 …
glt 发表于 2011-7-2 00:33

这是为了声音的细节，对于声卡来讲，小信号工作的时间更多。
MC33079小信号放大的性能远超OPA4134，其输入截止电压(OFFSET VOLTAGE)仅有0.15mv，对声音的细节刻画要远好于OPA4134和OPA4228。
乐之邦是一家崇尚技术和科学的厂家，会根据应用合理的使用元器件，而不是别人用什么，乐之邦就用什么。
这也是为什么乐之邦能经久不衰，把其他竞争对手相继甩开的主要原因。

Basically the MC33079 is a better fit to their system as compared to other “more popular” opamps such as the OPA4134. Key in their research is the “small signal” behavior and in particular the offset voltage. Looking at their data sheet, the OPA4134 has an offset voltage of 0.5mV  whereas the MC3309 has an offset voltage of 0.15 mV…

Input offset voltage translate into errors in an opamp circuit. According to this entry:

Another practical concern for op-amp performance is voltage offset. That is, effect of having the output voltage something other than zero volts when the two input terminals are shorted together. Remember that operational amplifiers are differential amplifiers above all: they’re supposed to amplify the difference in voltage between the two input connections and nothing more. When that input voltage difference is exactly zero volts, we would (ideally) expect to have exactly zero volts present on the output.

I suppose as a head amp, it is important to care about noise and offset voltage especially because the device is seldom used at full output (as in the case of a DAC alone) and the volume is controlled in the digital domain. In this two parameters, the MC opamp has better specifications than the OPA part. I believe the choice made by Musiland on the MC opamp makes good engineering sense.

Here is a photo of my own Musiland 03:

8/30/11: Becoming more available. You can purchase in Hong Kong for HK$1080 That is about US$ 140