E1DA Cosmos ADC

[AnalogSteph]

I can even wee on the plot when the display is ON and the difference between power brick . Great success!

I think you'll want to correct your typo there... Any UK-based readers are probably dying with laughter.

 

[IVX]

I get a THD+N of almost -111dB and this is only 3 dB shy of what Amir had. This is great!

try to increase the ADC input level up to .1-.5db to find the lost 3db

 

[horias2000]

try to increase the ADC input level up to .1-.5db to find the lost 3db

Yes, I will try to modify the ADC input range.

 

[FrenchFan]

Yes, I will try to modify the ADC input range.

Just a little calculator with E1DA box
It is wrote in octave but you can use with all language

Out for 200Kohms scaler input resistor

------Input------
Resistor = 200000 ohms
Temperature in °C = 25
E1DA adc Calibre in Vrms = 2.7
E1DA scaler gain in dB = 0
BW = 19980
------Resolve-----
Input rsistor Noise (Vrms) = 8.11151e-06
Noise in dBFS(ADC output) = -110.445

We are not far

 

[IVX]

FrenchFan, 2pA/Hz^.5 is the current noise of OPA1612, which needs to be included in the account.

 

[FrenchFan]

FrenchFan, 2pA/Hz^.5 is the current noise of OPA1612, which needs to be included in the account.

Hi Ivan

It's been 30 years since I did this kind of calculation.
You're making my old neurons move.

I did the calculation again with Stephan's simulator:

Helpful Audio-Related Calculators

The specs of the OPA1612:

In fact we have 50Khoms equivalent in input:

If I do not take into account the noise current
my little script gives me:

------Input------
Resistor = 50000 ohms
Temperature in °C = 25
E1DA adc Calibre in Vrms = 2.7
E1DA scaler gain in dB = 0
BW = 19980
------Resolve-----
Input resistor Noise (Vrms) = 4.05576e-06
Noise in dBFS(ADC output) = -116.466

Using Stephan's simulator

With I noise = 0 , we find the same noise voltage
of my resistor.

with dBV = -107.8

To adjust with what I measured (-104dBFS), I put
Inoise = 2.3nA/sqrt(HZ) (Which remains in the spec)

dBV = -95.5

So a difference of 107.8 - 95.3 = 12.3 dB

Which I add to -116.466 = -104.166 dBFS

This is not too bad as a measure result

 

[pma]

Big congratulations, @IVX . I am feeding your ADC with a terrible input signal with 10ns edges and hundreds kHz modulation frequencies, and it still holds strong and measures what it should, without spuriae. I think AP could only dream about such behavior.

 

[IVX]

BTW, I am trying some LPF proto, standalone one, with a switchable gain 2.5db/7db or 4.65V/8V with 9039S as an input DAC. That possible to use with AP as well, for instance, my old 2522 gen has THD+N 124.5db@1k after the LPF. Actually, the results below are limited rather by APU than LPF.

 

[BKDad]

BTW, I am trying some LPF proto, standalone one, with a switchable gain 2.5db/7db or 4.65V/8V with 9039S as an input DAC. That possible to use with AP as well, for instance, my old 2522 gen has THD+N 124.5db@1k after the LPF. Actually, the results below are limited rather by APU than LPF.

~ 1.8 KHz cutoff?? 2 KHz?

 

[IVX]

1k

 

[BKDad]

1k

I was just going by the looks of the plot. Looked like -3 dB was between 1.8 KHz and 2 KHz. But, you oughta know what you designed to!

Also, just curious - why LPF instead of BPF? I'd think that removing noise below the 1 KHz tone would be a good thing, too. Kind of an AES17-2015 supplement. The REW and other software notch would ignore what's in that notch window, while the BPF actually gets rid of the generator imperfections above and below the AES notch.

 

[johny_2000]

BTW, I am trying some LPF proto, standalone one, with a switchable gain 2.5db/7db or 4.65V/8V with 9039S as an input DAC. That possible to use with AP as well, for instance, my old 2522 gen has THD+N 124.5db@1k after the LPF. Actually, the results below are limited rather by APU than LPF.

So this is proto of the Ultra-low THD 1kHz Sine Wave Generator?

 

[IVX]

nop, it is the Low Pass Ffilter.

 

[johny_2000]

nop, it is the Low Pass Ffilter.

Is the USB connection for power?

 

[IVX]

right. A bit cleaner sine is achieved today(Tweak_9039 is used):

 

[johny_2000]

right. A bit cleaner sine is achieved today(Tweak_9039 is used):

Looks very promising. This unit, combined with a high performance DAC, is the absolute best competitor to the high performance AP analog signal generator, except in single frequency mode (note: the most useful). It's time to complete the project and bring to market a 1 kHz active LPF device for measurements.

 

[IVX]

 

[BKDad]

View attachment 400727

I'm no expert, but is this pinout for the audio connectors different from the A + K version?

 

[IVX]

it is 3.5mm jacks and not AK pinout but APU-like pinout.

 

[BKDad]

OK, that makes sense. If this becomes a commercial product for you, we'll need to get a cable to go between a #9039S and the LPF box. I guess that a balanced cable or two is needed for a #9039S to drive a balanced device under test from the AK output of the DAC anyway.

Gets complicated with all the cables! Still way more convenient and more reasonable for a hobbyist than an AP box. Not to mention the price difference.

BTW, ever see this one?

TI Differential BPF