PC Mirroring and E70

@matt, really great having pc mirroring back. I was wondering what sorts of numbers you were seeing with the E70 you bought fairly recently.

Hi @Moto, I have not tried the E70 specifically. Are you seeing something unexpected?

No. After trying lots of permutations on attenuation, I still can’t get snr better than 99db. That’s with balanced out, pins 2 and 3 into l+ and l- on my qa402. Tried pin 1 grounded and not to bnc shell. Not any significant difference.

Sorry, I might be missing something. I asked if you are seeing something unexpected, and you replied “no” but then you indicated you can get SNR better than 99 dB. Are those statements contradictory?

Not sure what results I should expect from the QA but a little surprised that the snr was so low and that I couldn’t find a configuration to get a better number given that I get so much better from another adc.

Hi @Moto, Are you sure that Windows isn’t doing a rate transcoding? That is a certain way to botch the SNR. If your DAC is showing 44.1 and your QA40x SW is at 48, then Windows will unhelpfully transcode it for you, and the results aren’t good. Most DACs that you plug into Windows default to a pretty lousy mode of operation, and the only way to know is via spectrum analysis.

Additionally, you have to make sure your windows volume is set to max, that Windows hasn’t decided to add “bass boost” or EQ etc.

So I left the city where the E70 is but here I have a QA403 and smsl su-9n. Using the same config, at 4v(-.5db) in to the QA(12dbv), atten at 18db, both QA and windows/dac at 48k full volume, no effects on, I get thd -128db and snr 110.5.
The results with Cosmos adc are thd -128.6 and snr 120.2db.
Is that what I shoukd expect from the QA403?

I don’t know as I don’t have this DAC. What are you seeing for THDN and SNR if you use an app like REW to generate the tone and the QA403 to measure the tone? In other words, do you think the mirror generation is deficient?

I thought you had the E70 Velvet which is very similar.
I can’t get a wiring config that gives me a decent balanced output measurement.
Using the rca out I get thd -121.7db and snr 116.4 when using PC mirroring. When I use REW to generate the tone, I get thd -122.7db and snr 117.2. This difference while not significant, is consistent over many runs.

The above is with a 5.8 dbv input signal at 6dbv fs.
If I change to 12 dbv fs of course the thd is better but the snr worse. The differences above between pc mirroring and REW remain though.

What is the optimal cable config for measuring balanced out from the dac into the QA403? I am still struggling with that.

Last question. In pc mirroring, if the QA is in Stop, but the GEN button is pressed is the signal meant to be on to the external dac?

Yes, I have an E70 but I haven’t used it since we did the last round of experiments here.

For cabling, I’d take the XLR and split it into the + and - (make sure the the adapter isn’t merging the - with ground). And then run the + and - into the + and - on the QA40x. And the ground to the BNC shell.

I just checked, and when mirroring, if the GEN button is toggled, then the mirroring starts/stop.

@matt, that is what I tried in the first example in this thread. I have an xlr connector with test clips on the leads and used that to connect to the QA + - inputs. Tried with the braid clip on and off the bnc shell.
Rca still much better.
Maybe I need to make up a cable with xlr and 2 bnc connectors. Hmmm.