QuantAsylum QA400 and QA401

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Bob Cordell

Member
Joined 2006
cordellaudio.com
loyaltolex said:
Thanks.
Re my comment - 6dB low; if the signal was sourced from a differential output pair, for any given output level ("the reference level") the voltage from only one of the BNC would be half of the total voltage across the differential pair, hence my comment, that unbalanced level (using one BNC) would be 6dB low from the "reference level".

I seem to remember seeing - many days back (read OP71 days) a topology for dual op amp creation of balanced outputs. Due to clever feedback application shorting to ground of the pin3 output increase the Pin2 output voltage by 6dB - thus the unbalanced output level always equalled the balanced level.

And for the record I refer to pin2/pin3 in the XLR/AES standard not the actual pins of the OP71!

Denis Bohn - if he is on this forum would be an expert on this.

Sound System Interconnection is still one of the best around imho
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I think the THAT Outsmart chip also does the balanced output function.

Cheers,
Bob
 
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Davey

Account Closed
Joined 2001
loyaltolex said:
I seem to remember seeing - many days back (read OP71 days) a topology for dual op amp creation of balanced outputs. Due to clever feedback application shorting to ground of the pin3 output increase the Pin2 output voltage by 6dB - thus the unbalanced output level always equalled the balanced level.
Click to expand...

As noted by other posters, that's not an uncommon configuration. It's implemented on Behringer device outputs...among others.

However, the QA401 does not have such a 6db "auto-correction" implementation. If you need that "extra" 6db, you'll need to adjust it manually.

Dave.
 
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Davey

Account Closed
Joined 2001
On to another topic: I've had to isolate my QA401 from laptop USB power and supply it externally (Schitt Wyrd in this case.) Some distortion making its way into the measurements if using my laptop power.

Dave.
 

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1audio

Member
Joined 2004
Paid Member
I believe the QA401 pushes the USB power spec. at a little over 500 mA. USB 2 is listed as 500 mA max. Most PC's have electronic disconnects that trigger at 1A but may trigger lower. If the supply is at the minimum spec. then odd things might happen. The best way to check would be to probe the +5V on the USB cable.
 
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benb

Member
Joined 2010
Davey said:
Thanks.

Plugging into my desktop computer yields a much better result, so it does appear my laptop computer (a fairly new Acer E-15) causes/accentuates the issue. Whether this is entirely USB power related is unclear to me.

Dave.
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Is this with the laptop running on its internal battery, or with the adapter (a SMPS, of course) plugged into the wall? I can imagine this could make a difference, maybe a big one. Of course the desktop also runs on a SMPS, but it might have better filtering.
 
jan.didden

jan.didden

AX tech editor
Joined 2002
linearaudio.net
Paid Member
kasey197 said:
I wonder why they didn't just use two USB ports to get round the power consumption issues.
:D 'Optional extra USB port for Xtra performance' :D
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I think at one time you could buy adapters that did this. It's not just soldering the wires together, it's more involved but definitely not rocket science. Don't know they still exist.

IIRC USB3 can source 1A but I don't know if that is enabled if you connect a USB2 peripheral to a USB3 port.

Jan
 
agdr

agdr

Member
Joined 2010
agdraudio.com
Davey said:
On to another topic: I've had to isolate my QA401 from laptop USB power and supply it externally (Schitt Wyrd in this case.) Some distortion making its way into the measurements if using my laptop power.

Dave.
Click to expand...

An interesting test sometime would be to put a powered USB hub between the laptop and the QA401. One thing that comes to mind is NwAvGuy's ODAC. Had problems for years with some USB ports requiring galvanic isolation (or a USB hub inserted) until and George B. and JDS labs tracked it down to ceramic capacitors on the USB power lines of a few laptops. The low ESR ceramics caused a voltage regulator in the ODAC to oscillate. They changed voltage regulators and the problem went away. Apparently they had to dissect a laptop causing the problem to find out what USB parts had been used.
 
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davada

R.I.P.
Joined 2004
jan.didden said:
I think at one time you could buy adapters that did this. It's not just soldering the wires together, it's more involved but definitely not rocket science. Don't know they still exist.

IIRC USB3 can source 1A but I don't know if that is enabled if you connect a USB2 peripheral to a USB3 port.

Jan
Click to expand...

The power with USB is negotiated. You get a certain amount of start up current, 100mA for USB2 and ask for more up to 500mA. I haven't looked to see what it is for USB3.

Here we go.

"Version 3.1 now supports 5 V, 12 V, and 20 V on the pins to allow the higher power output without excessive current, but even the current has been increased to a maximum of 5 A which is much higher than before."
 
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Davey

Account Closed
Joined 2001
agdr said:
An interesting test sometime would be to put a powered USB hub between the laptop and the QA401. One thing that comes to mind is NwAvGuy's ODAC. Had problems for years with some USB ports requiring galvanic isolation (or a USB hub inserted) until and George B. and JDS labs tracked it down to ceramic capacitors on the USB power lines of a few laptops. The low ESR ceramics caused a voltage regulator in the ODAC to oscillate. They changed voltage regulators and the problem went away. Apparently they had to dissect a laptop causing the problem to find out what USB parts had been used.
Click to expand...

Using a "powered USB hub" is essentially what I did by using the Schitt Wyrd. An external box like that off-loads all the power requirement from the laptop.

I suppose the ODAC anecdote you mentioned might be a similar issue, but I'm certainly not going to dissect my laptop for an equivalent troubleshooting routine. :) The workaround I have is perfectly acceptable in my case.

Dave.
 
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MarkS

Member
Joined 2004
Just to update on the Windows 7 x64 QA400 driver signature issues.

The manufacturer has since been in touch and supplied me with a new set of dual signed x86 & x64 QA400 drivers, which installed successfully and the QA usb box is now recognised by the QA software.

I’ve also run a number of shut down, disassemble, restart and reassemble tests with the Lenovo laptop and the QA usb box without any problems.

Hth.
 

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MarkS

Member
Joined 2004
I would observe that in the course of resolving this digital signature problem I've installed the QA400 software and hardware on a total of five computers, a desktop and two laptops running Win7 x64, a laptop running WinXP x32 and a iMac running WinXP x32 under VMWare.

The one thing they have in common is that they all show different shrapnel at the bottom of the screen for the same loop test with the supplied leads :D
 
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