magnetic BNC adapters- I can't say I have every seen one. Most are made from brass. Steel is too hard to machine for these applications. They are usually made on screw machines that crank out connectors in 100's per hour. You will find nickle plating even under the goals. The Nickle is slightly magnetic but not enough to show in this application.
The distortion created by magnetic conductors is quite low, well below the floor of a QA401. It may show up at about -150 dB but that is near the limit of the best known instrumentation and far below almost any active circuit.
RE saving the plots. There are several ways. Most of the time I just use the snipping tool in Win 10. Its the easiest. But you can also save to the clipboard and go from there with the QA401 software.
The distortion created by magnetic conductors is quite low, well below the floor of a QA401. It may show up at about -150 dB but that is near the limit of the best known instrumentation and far below almost any active circuit.
RE saving the plots. There are several ways. Most of the time I just use the snipping tool in Win 10. Its the easiest. But you can also save to the clipboard and go from there with the QA401 software.
I use MWSnap, a freebie screen grab prog that easily can be configured to always load at Windoze boot time...
A quick magnet test shows that the knurled twist ring on a bnc connector is steel, this is consistent across several brands of bnc connectors here, not that it matters at the end of the day...
I had a few RCA connectors, the cheap ones, with iron in them I suspect. The measurement system at that time was with Asus Xonar DX and ARTA. With that poor connectors and chinese iron conductors the noise and the thd increased with 20dB, from -100dB at -80dB. The same problem with the iron chassis of the amplifier. Maybe the connectors without magnetic field of the transformer they did not trouble.
Finally ordered some BNCmale-RCAfemale connectors from Mouser. My BNC connectors from the oscilloscope probes and tones generator are nonmagnetic indeed, or maybe very weak. Here in my town, I just found only strong magnetic BNC-RCA connectors.
Finally ordered some BNCmale-RCAfemale connectors from Mouser. My BNC connectors from the oscilloscope probes and tones generator are nonmagnetic indeed, or maybe very weak. Here in my town, I just found only strong magnetic BNC-RCA connectors.
Hi Demian
Just looking at your QA401 as a possible measurement solution and test rig for a production environment. You said that a compromise in the design was to derive the opamp power supply from the USB 5V supply which could only yield +/- 6.5V. Is it possible to improve the performance by bypassing the existing supply and running the opamps stage at +/- 12V ?
Also is it possible to controlled this device from C++ Builder ?
cheers
david
Just looking at your QA401 as a possible measurement solution and test rig for a production environment. You said that a compromise in the design was to derive the opamp power supply from the USB 5V supply which could only yield +/- 6.5V. Is it possible to improve the performance by bypassing the existing supply and running the opamps stage at +/- 12V ?
Also is it possible to controlled this device from C++ Builder ?
cheers
david
I had very little to do with the QA401 except suggesting to Matt to look at the AKM ADC's and DAC's. Matt at the QA web sight would be best suited to answer your questions. however the opamps are not inhibiting the performance of the QA401. The limitation is the available power from USB 2. More power would enable more features however the performance (THD and THD+N) is limited by the ADC and the DAC.
Demian or Everyman,
Do you know if QA is discounting the QA401 for DIYAudio folks? I'm interested in one though for me kind of pricey, but still good value, yes?
Is there anything else that can touch it's performance for under:
How much more Umphf....does the QA401 have versus QA400?
As I am a lowly QA400 owner.
Cheers,
Do you know if QA is discounting the QA401 for DIYAudio folks? I'm interested in one though for me kind of pricey, but still good value, yes?
Is there anything else that can touch it's performance for under:
$1000
$2000
$3000
That doesn't need to be refurbished or if someone gets lucky, etc.$2000
$3000
How much more Umphf....does the QA401 have versus QA400?
As I am a lowly QA400 owner.
Cheers,
Sync:
I believe you have at least one conventional analog analyzer in your collection. If so use it as a front end for your QA400. The weakness of the 400 is twofold. First Max input is limited. Second its distortion is not super low. The analog front end addresses both.
Duke Aguiar is writing an app note on using a QA401 with an AP1 this way. You get the best of both.
I believe you have at least one conventional analog analyzer in your collection. If so use it as a front end for your QA400. The weakness of the 400 is twofold. First Max input is limited. Second its distortion is not super low. The analog front end addresses both.
Duke Aguiar is writing an app note on using a QA401 with an AP1 this way. You get the best of both.
How about the RTX 6001? The diyAudio Group Buy is over, but RTX makes it available as a regular product. Performance is top notch, and it's a gazillion times more flexible than the QA thingies, because it works like a standard USB audio interface, so you're not locked in to the QA software.
just got a RTX6001, very early days but seems to be living up to its promise so far.
Hi Sync,
The RTX unit really does perform extremely well, certainly something I've waited for years to own but thought I never would. As etlasr has said, it is living up to it's promise with the only glitch resolved by the designer within a matter of days. Now I'm just waiting for the repair kit to arrive. Compare that with the normal case of having to return the instrument for repair.
Best, Chris
The RTX unit really does perform extremely well, certainly something I've waited for years to own but thought I never would. As etlasr has said, it is living up to it's promise with the only glitch resolved by the designer within a matter of days. Now I'm just waiting for the repair kit to arrive. Compare that with the normal case of having to return the instrument for repair.
Best, Chris
QA401 beginner questions
I finally pulled the trigger on a QA401. Early xmas present to myself (or at least that's how I'm rationalizing it ). I've read the user manual, familiarized myself with the software, and have acquired BNC cables and terminators. I've done some Googling about testing methodology, but before I start any actual measurements, I should probably ask some questions. I'll primarily be testing preamps and headphone amps.
First off, what output voltage amplitude(s) make for good diagnostics? I know consumer line level is 0.316 Vrms / 0.9Vpp. Are there others at which I should test?
When testing, should I bypass the input volume potentiometer? If not, is there a "sweet spot" of pot travel?
Lastly, when testing a preamp, what value load resistor should I use? For headphone amp testing I have 32, 80 and 300 ohm wirewound resistors.
Any other advice from QA401 users is most welcome
I finally pulled the trigger on a QA401. Early xmas present to myself (or at least that's how I'm rationalizing it ). I've read the user manual, familiarized myself with the software, and have acquired BNC cables and terminators. I've done some Googling about testing methodology, but before I start any actual measurements, I should probably ask some questions. I'll primarily be testing preamps and headphone amps.
First off, what output voltage amplitude(s) make for good diagnostics? I know consumer line level is 0.316 Vrms / 0.9Vpp. Are there others at which I should test?
When testing, should I bypass the input volume potentiometer? If not, is there a "sweet spot" of pot travel?
Lastly, when testing a preamp, what value load resistor should I use? For headphone amp testing I have 32, 80 and 300 ohm wirewound resistors.
Any other advice from QA401 users is most welcome
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Here is a pretty comprehensive guide: Sound System Interconnection Without knowledge of the other end of the XLR I'm not sure anyone can answer your question definitively but I think you want either configuration 1 (with the BNC's at the left side) or configuration 5. Common mode would be the defining issue. If there is significant ground currents between the boxes then #1. If they share a seperate ground #1. Otherwise read the article treating the two BNC's like a single XLR with the shields as pin 1. Let us know what worked for you.
I would correct that first. Connecting pin 1 to signal ground is a problem waiting to happen.
Jan
Well, SY made me do it?
http://syclotron.com/ImPassePreamplifier.pdf
I suppose pin 1 is in the completely wrong place, but I made a reasonable assumption.
I am connecting this to a pair of bridged F4, which on page 7 also implies pin 1 to ground, under the “mono balanced” configuration:
http://www.firstwatt.com/pdf/prod_f4_man.pdf
All that to say, I am getting a good amount of 60Hz on the FFT with the grounds of the QA401 connected pin 1 on both the input and output cable. The 60Hz isn’t present in loopback. It’s enough that it will interfere with my measurements. I will try a few things and report back.
http://syclotron.com/ImPassePreamplifier.pdf
I suppose pin 1 is in the completely wrong place, but I made a reasonable assumption.
I am connecting this to a pair of bridged F4, which on page 7 also implies pin 1 to ground, under the “mono balanced” configuration:
http://www.firstwatt.com/pdf/prod_f4_man.pdf
All that to say, I am getting a good amount of 60Hz on the FFT with the grounds of the QA401 connected pin 1 on both the input and output cable. The 60Hz isn’t present in loopback. It’s enough that it will interfere with my measurements. I will try a few things and report back.