AMB Ɣ2 technical measurements

amb Ɣ2 technical measurements

Standard Prologue
If you are unfamiliar with audio measurements please use a search engine with the query:
"audio measurements" or "audio measurement handbook"
Look for publications by Richard C. Cabot and also by Bob Metzler, both from Audio Precision. There are other useful publications as well. These will provide basic knowledge.
Interpretation of the following measurements is beyond the scope of technical measurements posts.

The data presented were collected as follows:
1. PrismSound dScope III, picoscope 5243B
2. Tecnec 75R spdif cable
3. Single Ended cables Mogami 2964 1 meter with Amphenol RCA connectors
4. 100 Kohm load used for measurements
5. dScope analyzer sample rate 48 KHz unless otherwise noted
6. DAC 44.1 KHz sample rate, 24 bit depth unless otherwise noted
7. Audioquest Forest and Schiit Pyst USB cables
8. Vaunix Lab Brick USB hub
9. Shielded 14AWG and 16AWG power cables
10. A filter mode unless otherwise noted
11. Soft clip ON unless otherwise noted

Measurements are made in accordance with AES17:2015

Measurements for record commenced after warmup of at least 48 hours.
Measurements were performed over a period of several months.

Index
Post 1 - measurement setup description, highlights
Post 2 - spdif input - SE RCA outputs
Post 3 - USB ASIO input - SE RCA outputs
Post 4 - Filter response part 1 - step response (square wave)
Post 5 - Filter response part 2 - Imaging
Post 6 - Anticlip feature
Post 7 - External Power Supply
Post 8 - Comparison with ODAC (Original Generation)
Post 9 - reserved for additional data and corrections

Notable highlights:
Ɣ2 is one of the better WM8741 DAC implementations.
spdif performance is decidedly better than USB.
Very low distortion.
Power supply noise spectrum is notably low for a SE output at -118 dBFS with spdif and external power supply.
SE output Dynamic Range of 121 dB.
SE output Cross-talk is approaching dual mono with > 125 dB isolation.
Very low jitter, especially with spdif input.

The AMB Ɣ2 preceded the ODAC by three years. Considering how NwAvGuy denigrated other DACs, the Ɣ2 embarrasses the ODAC both technically and in listening evaluations. See post 8 below for details.

2009 AMB Ɣ2 introduced
2012 ODAC introduced

amb Ɣ2:


Measurement setup example:


Listening evaluation example:


Ɣ2 is eminently listenable. USB implementation is dated, however spdif + external power supply allow the Ɣ2 to perform its best. A far better auditory experience than the Original Generation ODAC.

 

spdif input - SE RCA outputs

Ɣ2 Dynamic Range spdif input SE output

Excellent performance, especially considering SE outputs, size and price of this DAC.

Dynamic range, in simplified terms
1. find maximum output voltage at 0 dBFS
2. find residual noise with a -60 dBFS 1 KHz stimulus, removed from analysis by window notch
3. Dynamic Range is the difference between maximum output and residual noise
Specifics are in AES17 section 9.3 (measurebators do your homework please)
Example here:
https://www.maximintegrated.com/en/design/blog/spec-dynamic-range.html

Why we have a -60 dBFS stimulus
Some clever codec designers include an output gate that shuts off when there is no signal present. This has the dual benefit of lowering output idle noise while also gaming the measurements. spdif became wise requiring a -60 dBFS stimulus so any such gates are open during measurement and true Dynamic Range performance measured.

Ɣ2 A04 THD+N THD nth-HD FFT spdif input SE output


Ɣ2 50 + 7000 Hz spdif input SE output - Left Channel


Ɣ2 Gain Linearity spdif input SE output - Left Channel


Ɣ2 THD+N vs Frequency spdif input SE output - Left Channel


Ɣ2 Residual Noise SE spdif input SE output


Ɣ2 Inferred Jitter spdif input SE output

This is an exceptionally clean jitter measurement!

Complete spdif input SE output analysis report pdf attached

 

USB ASIO input - SE RCA outputs

Ɣ2 Dynamic Range ASIO input SE output


Ɣ2 A04 THD+N THD nth-HD FFT ASIO input SE output


Ɣ2 50 + 7000 Hz ASIO input SE output - Left Channel


Ɣ2 Gain Linearity ASIO input SE output - Left Channel


Ɣ2 THD+N vs Frequency ASIO input SE output - Left Channel


Ɣ2 Residual Noise ASIO input SE output


Ɣ2 Inferred Jitter ASIO input SE output

Again a very clean jitter response, especially from USB power!!

Complete ASIO input SE output analysis report pdf attached

 

Filter response part 1 - step response (square wave)

Measurement conditions
1. Ɣ2 gain set to A, B or C filter as noted
2. 44.1 KHz sample rate except where noted
3. USB ASIO input
4. SE output to oscilloscope
5. Ɣ2 anticlip on

Filter step responses are independent of inputs and outputs.

filter A Linear phase, slow rolloff
filter B Minimum phase, slow rolloff
filter C Linear phase, brickwall

Ɣ2 20Hz square -3dBFS ASIO input SE output - Filter A


Ɣ2 20Hz square -3dBFS ASIO input SE output - Filter B


Ɣ2 20Hz square -3dBFS ASIO input SE output - Filter C




At 0dBFS ringing is softly clipped:

Ɣ2 20Hz square 0dBFS ASIO input SE output - Filter A


Ɣ2 20Hz square 0dBFS ASIO input SE output - Filter B


Ɣ2 20Hz square 0dBFS ASIO input SE output - Filter C

 

Filter response part 2 - Imaging

Measurement conditions
1. Ɣ2 filter set to A, B or C filter as noted
2. dScope signal generator set to -6 dBFS white noise
3. 44.1 KHz sample rate except where noted
4. spdif or USB ASIO input
5. SE output to dScope
6. Ɣ2 anticlip on

filter A Linear phase, slow rolloff
filter B Minimum phase, slow rolloff
filter C Linear phase, brickwall

Ɣ2 imaging spdif 44K input SE output - Filter A


Ɣ2 imaging spdif 44K input SE output - Filter B


Ɣ2 imaging spdif 44K input SE output - Filter C



Ɣ2 imaging ASIO 44K input SE output - Filter A


Ɣ2 imaging ASIO 44K input SE output - Filter B


Ɣ2 imaging ASIO 44K input SE output - Filter C

 

Anticlip feature

Ɣ2 anticlip appears to reduce the output by 2 dB.
It does not appear to influence the soft clipping of filter ringing.

Ɣ2 SigGen gamma2 440 Hz sin 0dBFS 500uS div 5MHz filter ASIO SE - fltr A - anticlip off


Ɣ2 SigGen gamma2 440 Hz sin 0dBFS 500uS div 5MHz filter ASIO SE - fltr A - anticlip on


Ɣ2 SigGen gamma2 20 Hz sqr 0dBFS 200uS div 5MHz filter ASIO SE - fltr A - anticlip off


Ɣ2 SigGen gamma2 20 Hz sqr 0dBFS 200uS div 5MHz filter ASIO SE - fltr A - anticlip on


Ɣ2 SigGen gamma2 20 Hz sqr 0dBFS 200uS div 5MHz filter ASIO SE - fltr B - anticlip off


Ɣ2 SigGen gamma2 20 Hz sqr 0dBFS 200uS div 5MHz filter ASIO SE - fltr B - anticlip on


Ɣ2 SigGen gamma2 20 Hz sqr 0dBFS 200uS div 5MHz filter ASIO SE - fltr C - anticlip off


Ɣ2 SigGen gamma2 20 Hz sqr 0dBFS 200uS div 5MHz filter ASIO SE - fltr C - anticlip on

 

External Power Supply

Measurement conditions
1. Ɣ2 filter set to A
2. 44.1 KHz sample rate except where noted
3. spdif input
4. SE output to oscilloscope or dScope

An external power supply is only needed when the Ɣ2 is used with an input other than USB and is not connected to USB power. However Ɣ2 performs better with an external power supply and not connected to USB. When using USB input it appears that the Ɣ2 doesn't benefit from the external power supply.

I expected spdif operation with external power to behave better than USB powered operation. When considerably inconsistent measurements were obtained in succession, I knew something was amiss. This is why one doesn't just push the button, run a measurement, then post the result.

Here is an animation of Ɣ2 inconsistent dynamic range measurements acquired in rapid succession:

Those are wildly varying from 91 to 123 dB.

Ɣ2 residual noise also measured inconsistently:



-84 to -107 dBFS should make one suspicious that something is seriously wrong.

I began to suspect the external power supply. Attaching an appropriately sized resistor to create a load similar to the DAC, which is approximately 150 mA, power supply spectrum and time domain ripple measurements were observed.

Jameco power supply with 150 mA load - spectrum:

Clearly the spectrum is changing over time.

Jameco power supply with 150 mA load - time domain ripple:

Ripple varies over time from nearly ok to a decidedly horrible 100 mV.

It is likely that some component(s) in the Jameco power supply has deteriorated but not sufficient to cause complete failure. Keep in mind the Jameco power supply may be over 12 years old. The deficient behavior did not occur immediately but after approximately 15 minutes of warm up. Another good reason to warm up components before taking measurements for the record.

Switching to an iFi X power supply, DAC results improved greatly, yielding consistent results in successive measurements as observed below:

Ɣ2 dynamic range spdif in SE out


Ɣ2 residual noise spdif in SE out


Gain Linearity was also highly influenced by the power supply

Ɣ2 gain linearity spdif in SE out - Jameco power supply


Ɣ2 gain linearity spdif in SE out - iFi X power supply

Much improved performance when the compromised, aging power supply was replaced with the iFi X.

 

Comparison with ODAC (Original Generation)

Comparison of AMB Ɣ2 to ODAC (original generation, not necessarily representative of current ODAC versions)
NwAvGuy made considerable noise about the superiority of ODAC via design by measurements. The following comparisons reveal AMB Ɣ2 clearly measures better and preceded ODAC by several years. Someone didn't do their homework, or worse, purposely misled a large number of people.

Jitter

ODAC inferred jitter ASIO input SE output


Ɣ2 inferred jitter ASIO input SE output

Ɣ2 demonstrates superior jitter performance than ODAC

Ɣ2 inferred jitter ASIO input SE output

Ɣ2 jitter is better still with spdif and iFi X external power supply


Step Response (low frequency square wave)

ODAC step response 0dBFS ASIO input SE output

I have never observed this egregious behavior from any other DAC of the hundreds I have measured. ODAC oscillates between the two states during state transitions.

Ɣ2 step response 0dBFS ASIO input SE output

Ɣ2 behaves as expected with a single transition and the usual pre and post transition ringing consistent with a linear phase filter.

1KHz sine -90dBFS 16 bit performance

ODAC 1KHz sine -90dBFS 16 bit performance

Discrete bit levels are noisy and indistinct

Ɣ2 1KHz sine -90dBFS 16 bit performance

Each of the discrete bit levels are apparent and with much lower noise than ODAC

 

reserved for additional data and corrections

 

Have you measured an ODAC before? Maybe (also due to age?) its performance has deteriorated over time ...

Measuring another unit would provide confirmation (and the final nail in the coffin )

 

I will be publishing measurements from the OG ODAC I own in the near future. Along with Mousai msd192 which is another WM8741 implementation.

I have measurements from years ago and recent. They are not significantly different. I presented the step response oscillation years ago at an AES meeting.

 

His name is NwavDouche just for the record

Thanks or the measurements! Very cool to see proof of a conman.

 

This post is a great example that just looking at a certain set of data doesn’t tell you the full story.

From the FFT it appears that the γ2 is much worse than the ODAC. The time domain however shows a different story.

 

Was this unit with the optional SRC4192 ASRC?

 

Yes, this Ɣ2 has a BB SRC4192, as does the Walnut X.3, also an WM8741 based DAC as measured here.

 

That goes a long way to explaining the low jitter.

Excellent work as always!