Cosmos APU
Specifications:
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Device purpose
/marketing target: Cosmos Analog Processing Unit a single-channel device
top performance THD+N and Noise/DR measurement tool for Cosmos ADC
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Status: production
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Materials: Sandblasted/black anodized aluminum/laser mark/THAT1510/OPA1612/RT6863S
Viking resistors, Murata, TDK, ELNA caps, Taiwanese connectors and switches
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Dimensions: PCBA 90x50x29mm
104x61x39mm
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Weight: PCBA 34g
Assembled unit 157g
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Power: USB-C +5V rail, 350mA idle current, isolated power is recommended
(charger, power-bank >600mA)
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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.
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Outputs: 3.5mm jacks TRRS pinout as +Out/GND/GND/GND respectively
unbalanced up to 10Vrms, Zo = 47ohm
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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
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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
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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.
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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.
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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.
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Need more tech?
REW with the calibration file DAC+LPF->CosmosAPU->CosmosADC
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.
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).
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).
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.
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!
The PCBA adjustment is easy but please use a long sweep for the best results.