Cosmos APU/LPF

Cosmos APU

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Specifications:

Device purpose

/marketing target: Cosmos Analog Processing Unit a single-channel device

top performance THD+N and Noise/DR measurement tool for Cosmos ADC

Status: production

Materials: Sandblasted/black anodized aluminum/laser mark/THAT1510/OPA1612/RT6863S

Viking resistors, Murata, TDK, ELNA caps, Taiwanese connectors and switches

Dimensions: PCBA 90x50x29mm

104x61x39mm

Weight: PCBA 34g

Assembled unit 157g

Power: USB-C +5V rail, 350mA idle current, isolated power is recommended

(charger, power-bank >600mA)

Inputs: 3.5mm jacks TRRS pinout as +In/-In/GND/GND respectively

Notch: balanced (FDA) up to 10Vrms(active clamp to 15Vpeak)

gain = 20db + 0/6db(switchable), Zi=20/10kohm bal/unbal

the Notch ratio = -30db at 1kHz or 10kHz(switchable) Q = 50

Residual Noise 950nVrms(A) typical(gain 20+6db, Fnotch=1kHz)

Residual distortions: @1kHz@4.5Vrms 2nd/3rd <-150db/-150db

@1kHz@9Vrms 2nd/3rd <-150db/-150db

@10kHz@4.5Vrms 2nd/3rd <-130db/-130db

Residual THD+N BW20-20k@1kHz@9Vrms <-131db unweighted

(practically achieved with DAC+LPF source)

@1kHz@4.5Vrms <-127db unweighted(practically achieved with DAC+LPF

sourse)

Preamp: balanced (FDA) up to 3.5Vrms(10oHm to TVS clamped!), gain =

34/60db

Zi=47/23.5k bal/unbal, 100pF input capacitance i.e. able to use as a phono- preamp with no RIAA correction, which would be accuratelly applied in a digital domain.

Residual Noise <130nVrms(A) typical at +60db gain or <260nVrms(A) at +34db.

The practically achieved Dynamic Range AES17 in the cascaded Preamp->Notch

@1kHz -60dbfs(10mVrms) >153db(A), @1kHz -60dbfs(5mVrms) >150db(A)

Preamp inputs, just in case, have internal low-noise phantom power 48VDC+/-4V

2x6.8kOhm for use with condenser mics(Neumann, AKG, Rode, and so on).

The phantom power increasing the noise of the Preamp for 12nVrms(A) i.e.

130+12nV

Do not turn On that power without a mic connected, that may damage the device

tied to the APU's preamp input! Please wait for at least 10s after the phantom

power is Off, to safely plug/unplug anything to the Preamp input.

Outputs: 3.5mm jacks TRRS pinout as +Out/GND/GND/GND respectively

unbalanced up to 10Vrms, Zo = 47ohm

Frequency response: Notch: 5Hz-200+kHz Fnotch=1k

0db referred to 50Hz 1kHz -30db, 2kHz -0.5..-0.6db, 3kHz -0.2db

Preamp: 10Hz-1MHz+ -3db@60db gain, 10Hz-5MHz+ -3db@34db gain

The calibration file for Cosmos APU 1kHz Notch for REW

Reviews:

https://www.l7audiolab.com/f/e1da-cosmos-apu-2/

https://archimago.blogspot.com/2022/05/early-look-cosmos-apu-high-performance.html

Important notes

Please, before you decide to buy Cosmos APU, make sure that you completely understand what is it. Analog Processing Unit is the first in its kind device on the market, hence, you need to understand do you really want:
a) to do the measurement of your DAC/AMP distortions@1kHz/10kHz at <-150/-130db harmonics level, or THD+N@1kHz down to -132db. In that case, you need the Notch part of Cosmos APU.
b) measuring your DAC/AMP DR/SNR with the residual APU's noise 130nVrms(A) with the Preamp of Cosmos APU.
c) to rip vinyl records with the Preamp of Cosmos APU + Cosmos ADC with built-in DSP RIAA EQing. Please, check Cosmos ADC page to find the CosmosAdc_v13_RIAA.hex.
d) to use a Pro condenser mic with 48V phantom power with the Preamp of Cosmos APU.

Remember that the input voltage for the APU's Preamp should be <=3.5Vrms, and <=10Vrms for Notch. Overvoltage of inputs may damage the unit, as a result, usually, input 0603 10ohm resistors will be burned.

Often the 2nd harmonic(H2) APU performance strongly depends on the symmetry of your particular bench/setup, hence, it is a good idea to use a power-bank, USB ISO, or battery-powered laptop for the ADC after APU. Often, a symmetry-related issue would be noticed if H2 levels are different after changing the input polarity.

A good example of the extremely low distortions measurement you can find in Archimago's blog
https://archimago.blogspot.com/2022/05/musings-hunt-for-150db-thd-with-victors.html
Remember, it is not always a trivial task. One of the places where you can discuss tech details is our Discord channel or diyaudio.com thread

To avoid accidentally turning On the phantom-power and further damaging the DUT tied to the Preamp input, we placed the blocking red plastic bar into the 48V power switch. Please, take it out before working with a condenser mic. Never turn On the 48V power without a mic but if you did that, please do not insert the plug into the 3.5mm input jack at least 10s after 48V power is Off, or also, you can see the orange LED(48V auxiliary indication)D light inside of the jack, please wait for the light dimming down.

Need more tech?

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REW with the calibration file DAC+LPF->CosmosAPU->CosmosADC

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AES17 Dynamic Range test performs at -60dbfs level by measuring the THD+N A-weighted. That plot shows the residual THD+N (A) of the LNA at 1-10mV level sweep. 2mV corresponds 2V 0dbfs DAC like CS43131, and -82db needs to subtract 60db to get AES17 DR = 142db. A typical high-performance DAC with 5Vrms 0dbfs could be measured down to 150db and so on.

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MM 5mV 10ohm source APU gain 34db Cosmos ADC+digital_RIAA 1.7V sensitivity

THD+N -89db or -97.7db(A). Due to H2 and H3 being very low, SNR is also 97db(A).

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MC 250uV 10ohm source APU gain 60db Cosmos ADC 1.7V sensitivity, THD+N -66db or -78db(A).

Due to H2 and H3 being lower than the noise floor, SNR is also 78db(A).

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The gain of Cosmos APU preamp is +60db(1000x times), hence the scale units are nVrms(A).

After the APU unit turns On, you can see 5s of settling, from 6s the input noise reaches 130nV, about 9s 48V power was turned On, and after 1s reached 142nS. Hence, APU's phantom power adds just 12nV to the preamp noise, that's a nearly ideal result as I think The test was performed with a shorted preamp's inputs(In+ to In-) and biased to the GND by 2x6.8kOhm resistor as a dummy condenser mic.

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The PCBA without the case offered cheaper but uncalibrated i.e. need to adjust 4 trimpots

to set 1k/10k Notch's frequencies and -30db ratios for both. The best option for DIYers,

however, if you gonna deal with so crazy low noise/distortions you have to add some shielding

for the board anyhow!

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The PCBA adjustment is easy but please use a long sweep for the best results.

Cosmos LPF

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Ok, now we have instruments to measure ultralow harmonic distortions, what about the sine source for that? Here are a couple of options:
1) analog sine generator, RC structure around the opamp.
Pros: minimal possible harmonic distortions depending on the quality of the used opamp and capacitors/resistors. Inexpensive.
Cons: fine-tuning is required, and no software level/frequency control(pure analog thing). To get low THD the RC impedance is better to keep higher than we need for the lowest noise i.e. for THD+N.
2) DAC + Low Pass Filter, DAC's harmonics and noise are reduced higher than LPF cutoff frequency(1000Hz).
Pros: also minimal possible residual harmonic distortions depending on the quality of the used opamp and capacitors/resistors. Inexpensive, no fine-tuning is needed. The DAC gives us a software level control, THD+N vs level test is possible. Also, so-called anti-harmonic THD compensation technique is available or DAC's THD compensation(for ESS products, see 9039S). It's an easy way to get a stable sine gen with the lowest possible THD, and THD+N.
Cons: a single frequency 1000Hz LPF, requires a DAC(ideally if balanced one). DAC's harmonics were just reduced by the factors versus frequency. For example, H2 reduced for 8db, H3 for 16db, H5 25db etc. Anyhow we need a decent DAC to work with the LPF.

I have used DAC+LPF approach for years, the first time in my AC power regenerator project in the early 2000th(MCU 10bits PWM output turned to the .01% THD sine). Today I using DAC+LPF as a sine source to calibrate my Cosmos devices, and I found that idea works just fine at <-150db of harmonics level, and THD+N -131db(BW 20-20k) with no recalibration.

Cosmos LPF is a PCBA with 2 3.5mm jacks inputs, and 2 3.5mm outputs, powered by USB-C. We gonna supply that as PCBA with no case(the board contains only low-impedance networks, and may work at the workbench), however, Cosmos APU's case is suitable and you can ask our Aliexpress about that.

Cosmos LPF is a product for the DIY market, which means a potential user may read schematics, and get some clues about the unit.

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Specifications:

Device purpose

/marketing target: Cosmos Low Pass Filter

top performance THD/THD+N sine gen LPF stage for Cosmos APU/ADC

works with DACs as a harmonics+noise filter, AP SYS2522 gen+Cosmos LPF got THD+N -124db instead of original -118db.

Status: production

Materials: OPA1612/OPA1656

Viking resistors, Murata, TDK caps, Taiwanese connectors and switches

Dimensions: PCBA 90x50x29mm

Weight: PCBA 29g

Power: USB-C +5V rail, 180mA idle current, isolated power is recommended

(charger, power-bank >500mA)

Inputs: 3.5mm jacks#1 TRRS pinout as +In/-In/GND/GND respectively

LPF inputs Zin = 3.2/1.9kOhm Lo/Hi gain 2.5/7db THD<-150db. THD+N<-131db

and switchable Bal2Unbal stage Lch inputs gain 0db

3.5mm jacks#2 TRRS pinout as +In/-In/GND/GND respectively

switchable Bal2Unbal stage Lch or/and Rch inputs Zi = 670ohm gain 0db

See the schematic diagram above for more details regarding the 10poles switch

THD/THD+N measured with 9039S DAC

Outputs: 3.5mm jacks#3 TRRS pinout as +Out/-Out/GND/GND respectively

LPF balanced output up to 10Vrms, Zo = 200mOhm 100mA, Noise 1.2uVrms

3.5mm jacks#4 TRRS pinout as +OutL/+OutR/GND/GND respectively

Bal2Unbal stage unbalanced outputs up to 6Vrms, Zo = 100mOhm 100mA,

may drive headphones >32ohm. Noise 440nVrms

Practical results and the discussion you may find here or in our discord channel.