E1DA Cosmos ADC

[IVX]

Problem fixed. The rheophores of C15 were long enough to touch the case. APU, extracted from its case, works flawlessly with the power bank. I cut the excess wire and APU now is ok. For the rest, impeccable calibration, verified with REW. Always thanks.

Oh, sorry about that, the case tube is fully and thick anodized and even C15 pins were longer than I ordered, anyway the anodize can withstand and isolate them from GND shorting for some time. This is the first case like that, I'll cut pins from today just in case.

 

[IVX]

dear @IVX will the 3.5mm stereo to xlr male cable from apu to adc as per the attached image work ? there are no cables available with mono 3.5mm plug at one end and xlr at other end.

well, I don't know, do you have the pinout?

 

[Skj]

I just wanted to ask can we use stereo 3.5mm to xlr cable instead of mono 3.5mm to xlr for connecting apu to adc ? Can i power apu and adc from 4xAA battery pack ?

 

[staticV3]

I just wanted to ask can we use stereo 3.5mm to xlr cable instead of mono 3.5mm to xlr for connecting apu to adc ?

All 3.5mm plugs will work fine on the APU's outputs. TS, TRS, TRRS, it does not matter.
What matters is the pinout of the cable (which 3.5mm contact is connected to which XLR contact).

 

[Skj]

see there is no unusual pin out for xlr to stereo 3.5mm cable. it is always same. hot to tip, cold to middle sleeve and ground to ground sleeve. issue is that 3.5mm mono to xlr cable is not available. 3.5mm stereo to xlr is available. as per the pinned diagram in discord output from apu is through 3.5mm mono pin and input to adc is trough xlr male. wherein hot is connected to tip and cold and ground connected to sleeve of 3.5m mono. btw one more question ? can we keep the shielding floating at 3.5mm end ?

All 3.5mm plugs will work fine on the APU's outputs. TS, TRS, TRRS, it does not matter.
What matters is the pinout of the cable (which 3.5mm contact is connected to which XLR contact).

 

[Skj]

the input and output pin on apu are 3.5mm or 2.5mm ?

 

[Skj]

did anybody try usb audio recorder pro app for recording to android ? it bypasses android os.

 

[Skj]

any guide for recording from mic through apu ?

 

[IVX]

Skj, just in case: https://e1dashz.wixsite.com/index/cosmos-apu
We sell a short type of XLR_Female/3.5mm and XLR_Male/3.5mm cables, I take XLR_Female/3.5mm(), 3.5mm end to the APU, XLR female to the Rode mic 5m cable(has 2pcs in the giftbox), that 5m cable goes to the mic. APU to ADC needs XLR_Male/3.5mm cable. That's it. Be careful with the 48Vdc power, turn it On only if the mic is plugged in. Do not unplug the mic on the fly, switch the APU Off, wait for 15s, and next you can unplug the mic safely.

 

[Skj]

thanks a lot. there were issues mentioned earlier about poor measurements with SE out of dacs. will there be such issues with apu too as apu out is also se ?

 

[Skj]

Tried usb audio recorder pro Android app today with focusrite scarlet 2i2 interface. App bypasses android and allows to select stereo mono, input rate. Saves in flac and wav. So far not received cosmos adc so could not check it with cosmos adc. The app has very clean no nonsense ui, very simple to use. Best part it bypasses the Android.

 

[Skj]

Dear @IVX what is better, whether to float shield at "apu end" or to short it with cold wire coming from Xlr? I want the cleanest recording.

 

[IVX]

The rule is very common, there is nothing special. All Cosmos devices have balanced inputs only, hence, need to keep a balanced connection along the entire cable length. I.e. In+ and In- should be placed in the same position and inside the same shield. On an SE DUT site the In- should be tied to the GND. For example, this is a right way to connect Cosmos ADC in mono mode to the RCA.

 

[Skj]

To record guitars with passive pickups well (i.e. high and complex output impedance) you will need an interface with a very high impedance input - this is commonly marked as 'Instrument' or 'HiZ' inputs on professional audio interfaces.
Alternatively you could use a DI box to interface a high-impedance passive pickup to a low-impedance ADC input (such as the ones on Cosmos ADC).

Connecting a passive guitar pickup directly to the Cosmos ADC (i.e. without a DI box in between) will likely result in significant low-passing of the guitar signal, which will be an audible degradation of the signal - regardless of otherwise perfect AD conversion.
This would not happen with a pro audio interface with a HiZ input.
From that perspective the Cosmos ADC is not an ideal choice for this use-case, as you need an additional box to make it work well.

As far as pure audio performance specs are concerned, electric guitar is a very band-passed and relatively low-dynamic range instrument so most ADCs will be able to capture it cleanly - the Cosmos ADC is definitely an overkill for this; though I do appreciate the viewpoint of "better safe than sorry"

In summary almost any solid pro audio interface with a HiZ input will be OK to directly record electric guitar into - though I'd suggest interfaces with good SW support and low-latency drivers. Thus far my favorite manufacturer is RME, due to amazing SW support, good audio performance and rock-solid drivers.

BTW I measured audio performance of a lot of pro guitar gear, and I can tell you that in many cases you can be happy when SINAD reaches 60dB - no where close to the stellar 120dB of the Cosmos ADC. Still such gear is used on stages and studios around the world and no one is complaining.

Guitar means electric by default? Cosmos adc apu combo is great or even best source on earth for recording live performance through a pair of condenser mics. Many audiophile labels still do live recording through a single stereo mic without any processing at all. Chesky, waterlily acoustics to name a few.

 

[weme]

I am somewhat surprised at the voltage values listed (Mono). I had assumed that the Mono/Stereo switching was done internally in the ADC.
In Stereo Mode, I measure the same voltage values for L/R. The overdrive indicators works in Stereo Mode. In Mono Mode there is no display on the left (red).
Otherwise the ADCiso seems to function normally.

Who can clarify this?

 

[IVX]

not only internally, also needs to tie together L+R ADC's XLR i.e. both XLRs should have the same signal.

Cosmos ADC | index

e1dashz.wixsite.com

 

[weme]

Thank you for your spontaneous reply!

You don't give any error hints - so the ADCiso should be OK!?

Of course I have also read your notes on Mono/Stereo on your homepage and the Mono feed via Y-cabling is also clear. However, as I only work with single-channel or stereo signals, I have noticed the different voltage values.

BTW.:
I also like the new design of the ADCiso.
I would clamp the two USB cables between a small aluminium bracket and an aluminium strip. The aluminium bracket would then be screwed to the free thread. Or you could mount the ADCiso on a plate and clamp the cables there.

 

[IVX]

Sorry, I didn't understand your table above and just gave a very common hint which helps in 90% of cases. The link https://e1dashz.wixsite.com/index/cosmos-adc
contains all data needed to decide whether the unit is Ok or not, for example, there is a list of input impedances, and mono/stereo impedance difference is also noted.
If you have measured ADC's input voltage and found >.5db mismatch between channels dbfs or so, it is the ADC problem.

 

[weme]

You are right, my table was not readable (wrong labelling, just modified - indication of switch positions (6.7V |10V) was unnecessary). Hence this description:

A generator (Ri 200 Ohm, 1 kHz) is connected to ADCiso(Left) or ADCiso(Right) via XLR cable. The ADCiso is in Mono Mode. Measurements are made with REW (OS Ubuntu), voltage values are now normalised.

REW Input Device: R
REW RTA: ADCiso(R): 0 dB
REW RTA: ADCiso(L): only noise

REW Input Device: L
REW RTA: ADCiso(L): -6 dB
REW RTA: ADCiso(R): -6 dB

The switch positions of the ADCiso (6.7V to 10V tested) play no role in the 6 dB difference between the relevant voltage values.

On your homepage you write:
"... it is a MONO ADC with summed Left+Right inputs mapped on the Left channel (Right input is always mapped to the Right channel). In the MONO mode, both channels need to be tied together L+ to R+, L- to R-."

This circuit design probably leads to the 6 dB reduction.
I didn't want to use a Y-cable because of the further reduced input resistance.

 

[staticV3]

@weme maybe this helps clear things up:


If you want to use Mono mode for maximum ADC SNR, then you need to use a splitter to input the same mono signal to both Cosmos inputs.
You then analyze or record the Cosmos ADC's Left output channel, which will output the averaged/summed signal.

If you do not want to use a splitter, then Mono mode is useless and you're better off using Stereo mode on your Cosmos ADC.