If "I" am using 50 ohm terminators, why does this unit need the unused differential inputs shorted? When and why not? What is best 50 ohm vs 75 ohm? Short or no short? Hmmm? Confusion stirs in my mind...
Also, when you have +_ inputs AND +_ outputs "I" think it would be practical to share hook-up diagrams for specific scenarios. "I" feel the creators of this product are... I am reluctant to say this...arrogant and very advanced in engineering sciences. These people often find it less than themselves to share the basic user/interaction information as it may be less then they think. Rudimentary knowledge is hard to share when 'You' think your product is for genius thinkers like 'you'.
Why make a product to share with the layman and NOT make a layman's user guide? Why not make a product that is for 'everybody'?
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The QA401 is probably one of the most amazing DIY audio design test tool boxes ever made in a USB format for the price. "I" am certain the authors of this product could expand their client base 10x to 100x in 24 months if they embraced the very market the product fits into.
As an example of how head-in-*** these people are: when I received my brand new QA401 it(2"x4"x 8") was inside a cardboard box sliding around like a XXXX-ing 'Twist and Whirl' inside a ?????? 10"x5"x10" box!
The device I purchased was banging and slapping around inside a hollow posted cardboard box like it had the value of a corn on the cob. I HAVE NEVER SEEN ANYTHING LIKE IT!
I am sorry to post this but it is real.
Furthermore, when I got my slider slip pack QA401 in the mail I immediately contacted Quantasylum with my concerns via email...there is no PHONE NUMBER! Are you stupid or what?
In text, I received a third party 'voice' of a witness inquiry far distant from the actual hooligan that sent the shipment. Nobody at QA is actually there, they are kind of out of body when they write to you. The dialog I have in my email is like 3rd 4th 5th person disconnected from reality.
So here is my final review of the QA401:
Genius product for Genius users only....perhaps?
The manual is not a manual. It's a bla bla bla of features.
Product is amazing if you can find a friend to figure it out.
User MUST have 5-10 years practical lab experience with fine chemical and/or electronic scientific equipment usage of equipments
User must not email creator with questions(unless they are intelligent and prod thoughts in creator's mind)
Bla bla bla it goes on and on...
Also, when you have +_ inputs AND +_ outputs "I" think it would be practical to share hook-up diagrams for specific scenarios. "I" feel the creators of this product are... I am reluctant to say this...arrogant and very advanced in engineering sciences. These people often find it less than themselves to share the basic user/interaction information as it may be less then they think. Rudimentary knowledge is hard to share when 'You' think your product is for genius thinkers like 'you'.
Why make a product to share with the layman and NOT make a layman's user guide? Why not make a product that is for 'everybody'?
-----------------------------------------------------------------------------------------------
The QA401 is probably one of the most amazing DIY audio design test tool boxes ever made in a USB format for the price. "I" am certain the authors of this product could expand their client base 10x to 100x in 24 months if they embraced the very market the product fits into.
As an example of how head-in-*** these people are: when I received my brand new QA401 it(2"x4"x 8") was inside a cardboard box sliding around like a XXXX-ing 'Twist and Whirl' inside a ?????? 10"x5"x10" box!
The device I purchased was banging and slapping around inside a hollow posted cardboard box like it had the value of a corn on the cob. I HAVE NEVER SEEN ANYTHING LIKE IT!
I am sorry to post this but it is real.
Furthermore, when I got my slider slip pack QA401 in the mail I immediately contacted Quantasylum with my concerns via email...there is no PHONE NUMBER! Are you stupid or what?
In text, I received a third party 'voice' of a witness inquiry far distant from the actual hooligan that sent the shipment. Nobody at QA is actually there, they are kind of out of body when they write to you. The dialog I have in my email is like 3rd 4th 5th person disconnected from reality.
So here is my final review of the QA401:
Genius product for Genius users only....perhaps?
The manual is not a manual. It's a bla bla bla of features.
Product is amazing if you can find a friend to figure it out.
User MUST have 5-10 years practical lab experience with fine chemical and/or electronic scientific equipment usage of equipments
User must not email creator with questions(unless they are intelligent and prod thoughts in creator's mind)
Bla bla bla it goes on and on...
I read these amazing threads where designers share their secrets and many design details with students and laymen. There are some seriously cool sharing people on DIY AUDIO. That is a fact.
I think, if you share your idea here on your own volition, you should back it up and make it DIY AUDIO worthy.
Am I nuts? Am I the crazy person?
Jan, speak to my QA401 particulars to keep this on track.
I think, if you share your idea here on your own volition, you should back it up and make it DIY AUDIO worthy.
Am I nuts? Am I the crazy person?
That is exactly what I am referring to! Jan, you exemplify my thoughts with your curt educated reply."One" could also take the view that if "one" would need a drawing how to hook it up, "one" would most probably not be able to use and interpret results in an optimum way anyway...
Jan
Jan, speak to my QA401 particulars to keep this on track.
The QA401 people are not diyaudio. They need to worry about the next installment on their condo just like you and me so they must sell product.
They are not set up to handheld a beginning diyaudio enthousiast, although they have gone out of their way before to support us with advice and even with custom software adaptions. Above and beyond etc.
So I think your several negative posts are not justified.
Jan
The product is not expensive. It works as well as more expensive products, the manual is not very good. It is useless to measure are normal power without knowledge of input capacitance, the software caused many glitches with windows, installation was critical.
I received the product in a nice box with padding and probes. Everything was very professional.
To connect the product mr. mosfets you need bnc to rca. plug rca cable to amplifier input and voila. For the output you need probes set at 1X, do not use probe self reducer with power output, it doesn't work. Also it is very complicated to measure with resistor dividers because the QA has an input capacitor to reduce signal. it is complicated at this point.
I received the product in a nice box with padding and probes. Everything was very professional.
To connect the product mr. mosfets you need bnc to rca. plug rca cable to amplifier input and voila. For the output you need probes set at 1X, do not use probe self reducer with power output, it doesn't work. Also it is very complicated to measure with resistor dividers because the QA has an input capacitor to reduce signal. it is complicated at this point.
if you bought a good set of wrenches they won't come with instructions on how to replace a cylinder head gasket. I think that is the leap involved here. Its important to do homework before getting deep into testing. Many people have come up to speed and understand the complexity of the tasks but not without a lot of homework and experimentation.
On this type of instrument, whether its QuantAsylum, Jan Didden, RTX, AP, Shibasoku or the other options out there, the basic understanding that you know what you want to measure and the basics of that type of measurement is understood. The directions are to help the user find the expected connections and controls. Details like differential measurements and balanced vs. unbalanced drive are understood to be "prerequisites" to the task.
We can be very helpful on this forum if we understand the questions and your goals. This is a small niche with lots of specialized knowledge to be gained to get the best results. You are not the only one who is a novice at this and others can learn from your efforts. One of the challenges some of us have is that we have been doing this stuff for so long we don't know what we aren't explaining.
Users of the RTX are asking similar questions and we are trying to help them as well.
There are a few basic primers on making audio measurements. This is one that can be very helpful despite its age: http://lcweb2.loc.gov/master/mbrs/r...ektronix Cookbook of Standard Audio Tests.pdf and here is another more current example: http://www.ti.com/lit/an/slyt135/slyt135.pdf
On this type of instrument, whether its QuantAsylum, Jan Didden, RTX, AP, Shibasoku or the other options out there, the basic understanding that you know what you want to measure and the basics of that type of measurement is understood. The directions are to help the user find the expected connections and controls. Details like differential measurements and balanced vs. unbalanced drive are understood to be "prerequisites" to the task.
We can be very helpful on this forum if we understand the questions and your goals. This is a small niche with lots of specialized knowledge to be gained to get the best results. You are not the only one who is a novice at this and others can learn from your efforts. One of the challenges some of us have is that we have been doing this stuff for so long we don't know what we aren't explaining.
Users of the RTX are asking similar questions and we are trying to help them as well.
There are a few basic primers on making audio measurements. This is one that can be very helpful despite its age: http://lcweb2.loc.gov/master/mbrs/r...ektronix Cookbook of Standard Audio Tests.pdf and here is another more current example: http://www.ti.com/lit/an/slyt135/slyt135.pdf
First there is a power reducer, input capacitor and resistor to ground, then has a 220uf ? capacitor in serie and a 1k input serie resistor, goes to a buffer, 100ohm resistor serie then 33nf, then ADC input 720ohm.
If you divide the input power by 2, the ADC doesn't receive half the power at all frequencies.
Figure the ACD max input is 3Vpp into 720ohm, much attenuation of the input signal is required.
Mine has an input impedance of 100K in both attenuator positions. Some of the circuitry you are looking at is after the input buffer. The input has two ranges, 30V and 3V. Its a resistive divider. i would expect a trimming cap so the response is correct at both settings. The ADC has a passive low pass filter that works above 750 KHz and DSP for dealing with aliasing below that frequency. Nothing unusual in any of that. Mine is within 2% accuracy without additional calibration.
As soon as I have some bench space I'll reconfirm all of this.
As soon as I have some bench space I'll reconfirm all of this.
I assume you're talking about a Thevenin equivalent circuit by grounding the source end of your 2 ohm output impedance? (I think you might confusing yourself on the interfacing here.)
Anyways, I suggest to perform some sweep testing of the QA401 inputs with a 3rd-party generator of known flat response and low output impedance. You will find the QA401 input resistance is 100k ohms and flat as a pancake......just as Demian has alluded to.
Dave.
Hi gabdx
I think that you may be confused? A typical audio amplifier is a VOLTAGE OUTPUT DEVICE, driving a 2 Ohm load need output Z of < 10 to 1000x smaller than 2 ohms. If the output Z is 2 ohms the open circuit voltage could be 20 volts and with load only 10 volts. This would make the amplifier have very poor damping factor, run hot and sound bad along with other problems.
The amplifier driving the QA401 should not have a problem as loading the amplifier output.
Duke.
I think that you may be confused? A typical audio amplifier is a VOLTAGE OUTPUT DEVICE, driving a 2 Ohm load need output Z of < 10 to 1000x smaller than 2 ohms. If the output Z is 2 ohms the open circuit voltage could be 20 volts and with load only 10 volts. This would make the amplifier have very poor damping factor, run hot and sound bad along with other problems.
The amplifier driving the QA401 should not have a problem as loading the amplifier output.
Duke.
I would never drive the qa from the amp lol.
I mean that using a 1/8 divider doesn't translate in a 1/8 voltage divider because of the amplifier variable with frequency output impedance as well as the input of the buffer. You can try with your QA400. It is not a big deal though.
Why not? I do it all the time. That's one of the reasons the 20db pad was included in the QA unit. It's an excellent feature.
It seems to me you need to reassess your understanding of the interfacing involved here. I agree with Duke, it appears you're confused on the basics.
Dave.
Someone said they would test it.
load the amp with 8 ohm or watever you like and take the voltage from 1 ohm, calculate the voltage reduction and see if the QA watever model reads the proper value.
Well then, just fabricate yourself a simple -20db attenuator with say a 18k/2k resistor pad.
FYI, I just performed a quick test with my QA401 (attenuator off) with a 7 ohm / 1 ohm resistor pad. The plot shows -18db as expected across the frequency range.
Dave.
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Do you have a QA400 or a QA401?
The QA400 has a pretty low input max limit. However an input attenuator is pretty easy to fabricate.
You can't count on the QA400/401 to know that you have a passive attenuator. Further if you have 8 reasonably close tolerance 1 Ohm resistors the voltage across one is 1/8 the voltage across all 8. If you see a difference then something is suspect since Ohms law is pretty robust. However the difference between the open circuit output voltage and the loaded output voltage is indicative of the internal resistance of the amplifier.