Electronics > Projects, Designs, and Technical Stuff
Analog Disovery as Audio Analyzer
jaxbird:
--- Quote from: fivefish on December 15, 2015, 09:02:26 am ---jaxbird, big kudos to you on this project.
More questions: I assume the software will work with line level signals?
How about what if I need to measure DUT gear with balanced input/output, I'm thinking I'll need to convert the signals from the AD to balanced and vice versa before feeding it to the DUT gear. Have some kind of breakout box with the balanced converter circuits before the AD box? will that screw up the readings?
-- how about a "normalize" function, say measuring freq response, have the software automatically normalize the resulting curve to 0dB reference.
--- End quote ---
The Discovery got 2 differential inputs accepting up to +/-25V with 2 attenuation levels, to measure larger amplifiers more attenuation is needed.
For balanced signals, the differential inputs are fine, but for balanced output it would be best to add something like this:
You'd just need to check the Ref 1kHz box to set reference level at 1kHz level, otherwise it displays the voltage gain referenced to input level.
jaxbird:
--- Quote from: mtdoc on December 15, 2015, 08:45:36 am ---
I suspect there is no significant difference between hardware versions. Scope bandwidth on V2 is advertised as 20 MHz with BNC adapter on the NI website and 30MHz on Digilent's site. The spectral characteristics diagram for V2 on it's wiki page is the exact same as the one on page 16 of the V1 technical reference manual. In fact the V2 wiki looks to just be a web adapted version of this manual. Digilent made a silly marketing decision with V1 to market the scope as 5 MHz because they "did not want to confuse students" who might not understand the concept of a -3dB bandwidth. You can read this on page 16 of the technical reference manual.
I think once Digilent was bought by National Instrument, NI decided to put the AD in a new case and call it V2 with a more accurate bandwidth advertised. (though I question the 30 MHz bandwidth given the 100 MSPS for both scopes ADC, regardless of the -3dB measurement)
I'll be happy to be proven wrong but I think the only additional hardware of note is the addition of external power input to augment the power supply - the least useful feature of the AD IMO. Basically I think V1 = V2 just without the fancy case, ext power input and marketing fluff.
--- End quote ---
I wasn't even aware that NI had bought Digilent, but I guess they fit in nicely in the low end compared to Ni's more high end products.
I think you are right, they could have made some minor adjustments to the front end (just component values as the AD8066 should have enough bandwidth).
The added power supply features are probably worth the extra $20. I just had a look at microchipdirect.com, they used to sell the original for just over $200 to non students, but now it's the same $259 as everywhere else.
jaxbird:
--- Quote from: bson on December 15, 2015, 09:36:58 am ---
--- Quote from: jaxbird on December 15, 2015, 06:26:25 am ---In essence what you are saying is that there is no point in standardized testing of amplifiers as using resistive loads are not equal to speaker loads.
--- End quote ---
Yes. Did you follow the suggestion to run a simulation with different kinds of loads?
--- End quote ---
You seem persistent, so let's do a little experiment, instead of a simulation, to find out how much difference there really is and what it looks like.
Here is a comparison between using a typical small 2 way speaker with an impedance between 5 Ohm and 20 Ohm, compared to a 6 Ohm resistive load.
2 Way speaker's impedance for reference:
6 Ohm load resistor's impedance: (not very exciting)
Distortion measurement with Speaker load:
Distortion measurement with Resistive load:
The only difference here is that the amplifiers distortion is actually overall lower with the speaker load ;) Especially at the frequencies where the speakers impedance is higher.
timofonic:
269USD? I thought it would cost 100USD as much...
Is his really interesting?
miguelvp:
There is also the NI edition for students only:
http://sine.ni.com/nips/cds/view/p/lang/en/nid/213328
It does come with Multisim Student Edition as well.
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