Yes, please look here .http://www.diyaudio.com/forums/solid-state/248105-slewmaster-cfa-vs-vfa-rumble-320.htmlI have never used ARTA so i can't tell you if it is the software or not.
I know that it is a good program but I have never learned to use it.
Can you post a picture of your FR plot?
jer
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I will try with buffer and report again.Yes, not only does the buffer isolate the input impedance of the soundcard but it also isolates the changing impedance from the Cables Capacitance loading as well.
I believe that the cables capacitance is the biggest culprit now that you have brought it up.
jer
Regards.
Thimios.
Yes, I agree JCX there should be the ground hooked up going to the input of the sound card if any as that is its point of reference.
But, I have had it work without it just the same, although it can raise the noise floor as well making the measurements worse than what they really are.
I have had the very same setup not work the next day due to a movement of one of the power cables or something of that nature.
Ground Loops are a PITA but they must be understood in order to deal with them.
As I have mentioned before I have been slowly venturing in to the world of very small measurements and getting the noise floor low enough and my electrical surroundings quiet enough proves to be very challenging at times and changes from day to day.
CFL's are the worst!!!
jer
But, I have had it work without it just the same, although it can raise the noise floor as well making the measurements worse than what they really are.
I have had the very same setup not work the next day due to a movement of one of the power cables or something of that nature.
Ground Loops are a PITA but they must be understood in order to deal with them.
As I have mentioned before I have been slowly venturing in to the world of very small measurements and getting the noise floor low enough and my electrical surroundings quiet enough proves to be very challenging at times and changes from day to day.
CFL's are the worst!!!
jer
I'm so glad I'm not doing that as my day job anymore - that was well over a decade ago and I'm sure it's only getting harder to find "quiet".
Sounds like a case for pseudo-differential transmission.
Let's assume you have a resistor voltage divider at the amp output, R1 vs. R2.
Now what you need is a balanced input. (These can often take higher input levels as well.)
So how do you wire up your voltage divider for a balanced output (e.g. XLR female)? Simple:
Resistor divider output connects to "hot".
Amplifier output ground connects to "cold" via a resistor of value R1||R2. So if R1 = 10k, R2 = 1k, it would be a 909R.
Amplifier output ground connects to shield. (Shield may remain unconnected at input side.)
Impedance wise, this is perfectly balanced, so you get all the benefits of a balanced connection in terms of common-mode rejection.
If unbalanced inputs are all that you have, you must eliminate the ground loop in the test setup. When using a computer soundcard for everything, this would be expected to be running from output to amplifier to attenuator to input. That's why some people put a ~1k resistor in the ground connection before the input - basically they might just as well not connect it there at all.
Let's assume you have a resistor voltage divider at the amp output, R1 vs. R2.
Now what you need is a balanced input. (These can often take higher input levels as well.)
So how do you wire up your voltage divider for a balanced output (e.g. XLR female)? Simple:
Resistor divider output connects to "hot".
Amplifier output ground connects to "cold" via a resistor of value R1||R2. So if R1 = 10k, R2 = 1k, it would be a 909R.
Amplifier output ground connects to shield. (Shield may remain unconnected at input side.)
Impedance wise, this is perfectly balanced, so you get all the benefits of a balanced connection in terms of common-mode rejection.
If unbalanced inputs are all that you have, you must eliminate the ground loop in the test setup. When using a computer soundcard for everything, this would be expected to be running from output to amplifier to attenuator to input. That's why some people put a ~1k resistor in the ground connection before the input - basically they might just as well not connect it there at all.
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