E1DA Cosmos ADC

[pkane]

Then Cosmos is unable to be used with most DACs in unbalanced operation? Anyone here cares to actually test some DACs in on RCA outputs, please?

Is the ADC running in mono or stereo mode when you’re testing unbalanced?

 

[pkane]

Then Cosmos is unable to be used with most DACs in unbalanced operation? Anyone here cares to actually test some DACs in on RCA outputs, please?

Here's what I did: I connected half of the balanced output from ADI-2 Pro to the Cosmos ADC (ground and -, leaving + disconnected). ADC was in mono (summing) mode.

EDIT: updated captures to be at the same dBFS level due to balanced/single-ended differences.

The result:

With a fully balanced connection:

 

[trl]

Paul, in both situations I get same huge harmonics.

Now related to changing Cosmos's scale, to get a higher input impedance, here's the highest one:

ODAC v1 - Cosmos ADC on 10V RMS scale
​

Although I do understand that Cosmos's input impedance is very low indeed and per ODAC's designer "The ODAC can be connected to any input that accepts standard Redbook 2 Vrms line level audio and has at least a 10K input impedance" (source: http://nwavguy.blogspot.com/2012/03/odac-update.html) I still think that Cosmos should be able to measure all DACs properly, at least on the 10V scale where I see no improvement.

Per https://e1dashz.wixsite.com/index/cosmos-adc Input ranges/impedance:
1.7Vrms 640Ω
2.7Vrms 1kΩ
3.5Vrms 1.3kΩ
4.5Vrms 1.66kΩ
6.7Vrms 2.46kΩ
7.6Vrms 2.82kΩ
8.5Vrms 3.12kΩ
10Vrms 3.48kΩ
43Vrms 13.6kΩ
Note: unbalanced impedance about 30% less.

However, on Burson Conductor V2+ (TO92 transistors buffer) and on ODAC v1 I can't measure unbalanced DAC-out with Cosmos ADC due to the above issues, but on Topping D90 and ASUS Essence One (LME4562 buffer) I can measure perfectly.

 

[IVX]

@IVX, sometimes reading the various settings returns bogus values (usually but not always zero). What's with that? It happens with both your tweak application and mine.

I suspect the HID implementation in the chip.

 

[IVX]

Since Day1 I had troubles measuring non-balanced signals. On Motu M4 and Clarett 2Pre I get very good results, while on Cosmos ADC I get crappy ones, see below:

View attachment 163423
ODAC v1 measured on Cosmos ADC (1 ch., Stereo mode) - SINAD of 45.5 dB

View attachment 163424
ODAC v1 measured on Motu M4 Input #1 - SINAD of 95 dB
​

What am I doing wrong? It doesn't matters if I'm using an RCA - XLR cable (V+ connected to hot, V- connected to GND) or the default Cosmos ADC cables with spades, I get the same huge harmonics. It happens on all DACs but Topping D90 MQA (which has a very low output impedance).

Any thoughts, please?

​

ODAC v1 contains no any opamps-buffer at all just 220ohm in serial to pcm5102. Even 10k will affect the THD performance there, it is such a kind of junk-DAC, you can try to measure that at 10V ADC setting.

 

[mansr]

ODAC v1 contains no any opamps-buffer at all just 220ohm in serial to pcm5102.

Ugh.

 

[IVX]

I believe, ODAC v1 is such a DAC which really helps to hear the difference between an RCA audio cables ))

 

[audiofun]

ODAC v1 contains no any opamps-buffer at all just 220ohm in serial to pcm5102. Even 10k will affect the THD performance there, it is such a kind of junk-DAC, you can try to measure that at 10V ADC setting.
View attachment 163554

the one you had is a v2. v1 is similar.

sdac is significantly better is that respect.

 

[trl]

you can try to measure that at 10V ADC setting

I did already Ivan, see my above graph; sme huge harmonics. Same thing happens with another DAC that has a discrete output buffer made of TO92 transistors, so quite a beefy buffer.

 

[trl]

Ugh.

There are opamps inside the DAC chip itself, it's normal this way.

 

[IVX]

trl, Remember, XLR GND and In- should be shorted at the unbalanced DUT side.

 

[trl]

Did that already, thank you, but I'm not getting any improvements. I'll still dive deep into this. However, if this is really from the low input impedance of the Cosmos ADC, then there will be more audio sources that will not be able to work properly on Cosmos. After all, I guess AP devices are having an input impedance of 100 kOhms for a reason.

 

[IVX]

sure, on the other hand, you can quickly detect junk DACs that have troubles being loaded at a few Kohms.

 

[MC_RME]

Per https://e1dashz.wixsite.com/index/cosmos-adc Input ranges/impedance:
1.7Vrms 640Ω
2.7Vrms 1kΩ
3.5Vrms 1.3kΩ
4.5Vrms 1.66kΩ
6.7Vrms 2.46kΩ
7.6Vrms 2.82kΩ
8.5Vrms 3.12kΩ
10Vrms 3.48kΩ
43Vrms 13.6kΩ
Note: unbalanced impedance about 30% less.

These values represent stereo mode (1 input used) and balanced. If you measure mono, by splitting the signal to both XLR inputs, you get half these values, 1.4 k Ohms for 7.6 V rms.

For unbalanced the normal connection method (with standard cables and adapters) is to short XLR pin 3 and 1. The input impedance at 7.6 V setting then drops to 1.68 k Ohms stereo (40% less) and 840 Ohms in mono mode. At lower level settings you get definitely screwed.

You can stay at the higher impedance values by using Ivan's 'measure the unbalanced signal balanced' method (TM and pat pend), by using only input pins 2 and 3 for the unbalanced signal.

 

[solderdude]

@trl When you want to know if the ODAC has issues with the low load simply use the Motu and put a 1k resistor in parallel to (both) outputs and see what the Motu shows.

 

[trl]

sure, on the other hand, you can quickly detect junk DACs that have troubles being loaded at a few Kohms.

ODAC and Objective2 are the first interesting DIY audio projects in the world that proved audio transparency baked up by measurements done with AP equipment and these audio devices started a hole new generation of objectivists audiophiles! Based on AP's measurements made by its designer, ODAC is a transparent-enough DAC; in an A/B test, with FLAC songs, I can't tell which one is ODAC and which one is D90.

Ivan, don't get me wrong here, I DO LOVE COSMOS ADC and I consider it's the most affordable audio measuring equipment in the world, but given that AP, dScope and Quantasylum devices are all having a default input impedance of 100 kOhms what do you think of adding a switchable input impedance on a future Cosmos ADC, like dScope Series III has: "100kR, 600R or 150/200R (jumper)"?

However, looking for others to see if they encounter impedance issues, hope I'll be the only one having issues here.

Thank you for understanding!

 

[Rja4000]

I'll be the only one having issues here.

You're not.
Let's call it a "point of attention"

 

[IVX]

trl, if I want to keep max voltage 10Vrms, I need to make +/-16VDC(instead of +/-6.5VDC now) rails inside of COsmos ADC for the buffers. That dramatically increases the current draw and actually may reach USB2(500mA) or even USB3(900mA) limit. Technically it is a trivial task but seems I'll not able to offer you so simple USB-C power.

 

[Rja4000]

trl, if I want to keep max voltage 10Vrms, I need to make +/-16VDC(instead of +/-6.5VDC now) rails inside of COsmos ADC for the buffers. That dramatically increases the current draw and actually may reach USB2(500mA) or even USB3(900mA) limit. Technically it is a trivial task but seems I'll not able to offer you so simple USB-C power.

I hope if you do a "pro", 1U rack version, it will include a PS or be powered by PD USB-C.

 

[staticV3]

ODAC and Objective2 are the first interesting DIY audio projects in the world that proved audio transparency baked up by measurements done with AP equipment and these audio devices started a hole new generation of objectivists audiophiles! Based on AP's measurements made by its designer, ODAC is a transparent-enough DAC; in an A/B test, with FLAC songs, I can't tell which one is ODAC and which one is D90.

Ivan, don't get me wrong here, I DO LOVE COSMOS ADC and I consider it's the most affordable audio measuring equipment in the world, but given that AP, dScope and Quantasylum devices are all having a default input impedance of 100 kOhms what do you think of adding a switchable input impedance on a future Cosmos ADC, like dScope Series III has: "100kR, 600R or 150/200R (jumper)"?

However, looking for others to see if they encounter impedance issues, hope I'll be the only one having issues here.

Thank you for understanding!

The Cosmos ADC was intended as a tool for E1DA customers to calibrate their 9038S and 9038D units, which have an output impedance of .1/.07Ω, and so input buffers would've only reduced the dynamic range.

The input impedance is clearly stated on the website and the AliExpress shop, so it should be easy to decide whether the Cosmos ADC is the right tool for you.

A future Cosmos ADC Pro with buffered inputs and gain control via UAC2 is planned.