Hi, i just got a QA401 and I have a few questions. To begin I was measuring voltages at about 8-9VDC through the input before I realized the max input voltage is 5vDC. I was a fool to not check the manual for this. I wasn't concerned because the attenuator shut itself off and didn't reengage after the initial click but after a few measurements it was showing a red error on screen that said "input clip" with high levels of harmonics on screen.
So I stopped DC coupling it after that but I am wondering if this could have damaged the unit? The manual says the input is clamped to 7V but while it seems to work still I am measuring higher noise floor than I was before, should I be concerned?
Also before this incident even happened I took a look at the signal generator from the QA401 and I noticed that the signal keeps shutting off and on in 1sec intervals, this happens on all of the output terminals. Is this supposed to happen?
So I stopped DC coupling it after that but I am wondering if this could have damaged the unit? The manual says the input is clamped to 7V but while it seems to work still I am measuring higher noise floor than I was before, should I be concerned?
Also before this incident even happened I took a look at the signal generator from the QA401 and I noticed that the signal keeps shutting off and on in 1sec intervals, this happens on all of the output terminals. Is this supposed to happen?
Yes that behaviour is intended by QA. The unit samples exactly the number of samples thst is required for the FFT.
The inputs are AC-Coupled via 6V3 electrolytics, therefore the time-delay you have observed.
well I will tell you exactly what is happening with my divider, probably it is a resistor mismatch, nothing very dramatic I believe, but still to confirm.
Hi All
Food for though: Attenuator parts need to have good and stable properties to maintain GREAT PREFORMANCE. Choosing the resistors need tight tolerance and low ppm count or you will a poor PAD. Using an unknown type you can get a tight resistance value and poor ppm count (Change in value as temperature changes, like self-heating).
Dale/Vishay CMF 60 D, C, E are 1/4W to 70 degrees & 1/8w @125 degrees and 100 ppm, RN60C 50 ppm and RN60E 25 ppm.
I have attached a Linear Translator that may give some insight to this accuracy problem.
Duke
Food for though: Attenuator parts need to have good and stable properties to maintain GREAT PREFORMANCE. Choosing the resistors need tight tolerance and low ppm count or you will a poor PAD. Using an unknown type you can get a tight resistance value and poor ppm count (Change in value as temperature changes, like self-heating).
Dale/Vishay CMF 60 D, C, E are 1/4W to 70 degrees & 1/8w @125 degrees and 100 ppm, RN60C 50 ppm and RN60E 25 ppm.
I have attached a Linear Translator that may give some insight to this accuracy problem.
Duke
Hi gabdx,
I bought some cheap 100 watt metal ones (8R and 4R) that cost me $7 each. Outstanding value. Yes, no matter what dummy load resistor you buy, it must be mounted to a heat sink. There are some tubular ones available good for 175 watts that are convection cooled. They might work and they're a lot less expensive than mine. Currently the price for the Dale resistors I have is only $60 some odd each.
It cost me another $40 each for the heat sinks to be milled flat. The mounting surface is large, so it has to be machined to be flat or you won't get the thermal performance you expect.
One of my guys blew one resistor up. I was impressed. All I could do was laugh. That cost me $50 at the time, probably 33 years ago now.
-Chris
I bought the industry standard Dale 250 watt, 8R 1% dummy loads and they have performed perfectly for 30 some-odd years now. There are some less expensive ones that perform better than the 10 watt resistors. Those can change value quite a lot with temperature and are typically 5% or 10% ... or 20%.
I bought some cheap 100 watt metal ones (8R and 4R) that cost me $7 each. Outstanding value. Yes, no matter what dummy load resistor you buy, it must be mounted to a heat sink. There are some tubular ones available good for 175 watts that are convection cooled. They might work and they're a lot less expensive than mine. Currently the price for the Dale resistors I have is only $60 some odd each.
It cost me another $40 each for the heat sinks to be milled flat. The mounting surface is large, so it has to be machined to be flat or you won't get the thermal performance you expect.
One of my guys blew one resistor up. I was impressed. All I could do was laugh. That cost me $50 at the time, probably 33 years ago now.
-Chris
Hi Chris, I am reading that thread on the 'cables influence sound' on the forum and it is very polemic. Maybe this is what influences my readings, I am talking very small differences, it could be that the divider create another type of distortion with the cable lenght. Anyway it is a mind opener for me because I don't have any logic explanation. All you guys told me the QA is fine. I just don't know.
I wouldn't use round resistors cause they are inductive and super expensive. I was using those in calibration and they are over 100$ a piece. I always carried a couple massive ones to test high voltage equipment, like 100 watts ones
.
Talking about resistors, I actually found one type which sounds super nice. I prefer them to the PRP and all boutique ones (caddock, dale, etc) building feedback less preamp cards and dac modules with 3 different types, I prefer by far the sound of fireproof gray resistors with metal film 1/2 watt. However for tube stuff they can only be used for around 150V, I use special certified 600V ones for critical parts which also sounds better than // cheap resistors.
I wouldn't use round resistors cause they are inductive and super expensive. I was using those in calibration and they are over 100$ a piece. I always carried a couple massive ones to test high voltage equipment, like 100 watts ones
. Talking about resistors, I actually found one type which sounds super nice. I prefer them to the PRP and all boutique ones (caddock, dale, etc) building feedback less preamp cards and dac modules with 3 different types, I prefer by far the sound of fireproof gray resistors with metal film 1/2 watt. However for tube stuff they can only be used for around 150V, I use special certified 600V ones for critical parts which also sounds better than // cheap resistors.
Hi gabdx,
Yes, the high voltage resistors have to be that way, and are therefore more linear.
The tubular resistors I was referring to are much less expensive than $100. They will be slightly inductive, but not enough to matter. If you test high power at higher frequencies, you would probably burn out the zobel networks in a solid state amplifier.
I'll have to have a look at that thread, but I find that wire, unless it is a stupid type (like co-ax, individually insulated strands or similar) doesn't have any effect unless it is too small and has high resistance. What matters more is the connection and crossover (in a normal speaker). Of course, high levels of RF could cause trouble that a shielded cable solves. Then of course it comes out the "winner". Common sense really should dictate what wire you use.
-Chris
Yes, the high voltage resistors have to be that way, and are therefore more linear.
The tubular resistors I was referring to are much less expensive than $100. They will be slightly inductive, but not enough to matter. If you test high power at higher frequencies, you would probably burn out the zobel networks in a solid state amplifier.
I'll have to have a look at that thread, but I find that wire, unless it is a stupid type (like co-ax, individually insulated strands or similar) doesn't have any effect unless it is too small and has high resistance. What matters more is the connection and crossover (in a normal speaker). Of course, high levels of RF could cause trouble that a shielded cable solves. Then of course it comes out the "winner". Common sense really should dictate what wire you use.
-Chris
Hi Demian,
I have got the software. I asked quantasylum support and they loaded it up. I have got the manual too, but it´s not to easy to work with. For me it´s difficult to understand the level settings for example in the FR measurement modus. What is the output level?
Second problem: The QA 400 is made to work with Hi Z inputs. But they write in their manual an output impedance of 68 Ohms, which is quite low I think. Is it possible to measure low impedance studio gear with input impedance of ca. 2kOhm?
thankyou for help
best regards
jo.
I have got the software. I asked quantasylum support and they loaded it up. I have got the manual too, but it´s not to easy to work with. For me it´s difficult to understand the level settings for example in the FR measurement modus. What is the output level?
Second problem: The QA 400 is made to work with Hi Z inputs. But they write in their manual an output impedance of 68 Ohms, which is quite low I think. Is it possible to measure low impedance studio gear with input impedance of ca. 2kOhm?
thankyou for help
best regards
jo.
Some ASIO in Sunday's 1.613 preview release
Hmm.... yeah just getting caught on Github on all that has happened since the last stable V1.51 last year! Wow.
Releases * QuantAsylum/QA401 * GitHub
All preview, but some major positive changes, fixes, and additions it appears. Lol including just making it work again at all after the Windows 1803 "bomb" went off. Thank heavens I'm still on Win 7 on the laptop. Sounds like a new stable release (since 1.51) is imminent.
In Sunday's V1.613 preview, right at the bottom of the list, I see:
Added ASIO driver. Only left channel 48K atten active is functional right now. See "readme" in driver directory for instructions on how to install as its not installed by default. This driver won't be actively supported by us,, but we'd love to hear from you if it works as provided. With this driver, you should be able to move back and forth between Arta and the QA401 software. Note, though, that both apps cannot be running at the same time. if you have an Asio app open and try to open the QA401 app (or vice versa), the USB open will fail.
Cool! V1.60 Preview from March seemed to really be the start of the new code development effort, adding multitone and a bunch of other stuff. Looks like the '401 is getting beefed up!
Hmm.... yeah just getting caught on Github on all that has happened since the last stable V1.51 last year! Wow.
Releases * QuantAsylum/QA401 * GitHub
All preview, but some major positive changes, fixes, and additions it appears. Lol including just making it work again at all after the Windows 1803 "bomb" went off.
Thank heavens I'm still on Win 7 on the laptop. Sounds like a new stable release (since 1.51) is imminent.In Sunday's V1.613 preview, right at the bottom of the list, I see:
Added ASIO driver. Only left channel 48K atten active is functional right now. See "readme" in driver directory for instructions on how to install as its not installed by default. This driver won't be actively supported by us,, but we'd love to hear from you if it works as provided. With this driver, you should be able to move back and forth between Arta and the QA401 software. Note, though, that both apps cannot be running at the same time. if you have an Asio app open and try to open the QA401 app (or vice versa), the USB open will fail.
Cool! V1.60 Preview from March seemed to really be the start of the new code development effort, adding multitone and a bunch of other stuff. Looks like the '401 is getting beefed up!
