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Another video on Spectral Analysis for audio

97.95.43.235
Posted on May 22, 2016 at 00:01:29
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 I like this particular unit but using PC based sound cards can be challenging when testing power amps if you don't pad the inputs. It would be nice they made one ready to go because most of us that do this a lot tend to make mistakes due to fatigue and there goes the sound card.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

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RE: Another video on Spectral Analysis for audio, posted on May 22, 2016 at 00:48:23
Triode_Kingdom
Audiophile

Posts: 10049
Location: Central Texas
Joined: September 24, 2006
 I run my card from a box on the test bench that has an input pot on the panel. Whenever I change connections or amplifier settings, I just turn the pot down all the way. I tried clamping diodes at one time, but they introduced measurable distortion, even when signals were below the threshold. The best protection for the soundcard IMO would be an ultra low distortion opamp positioned ahead of the card. If the amplifier were powered by a low voltage +/- supply, that would prevent excessive output. The soundcard I use has the specs below. All the dedicated gear I've seen that beats this is much more expensive, even on the used market. Most of it also won't calculate THD and IM.






 

RE: Another video on Spectral Analysis for audio, posted on May 22, 2016 at 01:22:04
LinuxGuru
Audiophile

Posts: 582
Location: European Union
Joined: November 11, 2008
 1) Link to video is not shown (at least on Mozilla Firefox).

2) Pete Millet designed and made excellent sound card interface for PC card exactly for the purpose of measuring THD / IMD.

http://www.pmillett.com/ATEST.htm

http://www.diyaudio.com/forums/tubes-valves/155405-test-measurement-interface-soundcard.html

 

The link is OK, posted on May 22, 2016 at 08:11:18
Triode_Kingdom
Audiophile

Posts: 10049
Location: Central Texas
Joined: September 24, 2006
 I can view it; Firefox 46.0.1 & Win XP.

 

RE: Another video on Spectral Analysis for audio, posted on May 25, 2016 at 08:27:26
TRUFI
Audiophile

Posts: 622
Location: So. California
Joined: March 16, 2002
 I am looking into PC test analysis. Check out the the link below for the Virtins DSO. With a PC and the included software, this device functions as an oscilloscope, spectrum analyzer, multimeter, data logger, signal generator. No sound card required.

Anyone have comments or experience with these units?

 

RE: Another video on Spectral Analysis for audio, posted on May 25, 2016 at 15:25:56
Triode_Kingdom
Audiophile

Posts: 10049
Location: Central Texas
Joined: September 24, 2006
 It's my opinion a dedicated analog scope will serve you better as a primary instrument. The VT's 100V input rating is somewhat lacking for tube work. Also, the full-scale sensitivity of 20mV (+/- 10mV) might make some measurements difficult. My 30-year-old scope is capable of 500uV/division (4mv full scale) with a 1:1 probe. I would often need an external, low-noise amplifier to see hum and noise if not for that.

I think the VT might be useful for PC-based spectrum analysis and distortion measurements. These functions could overcome some of the limitations of the scope, although I would want to know if the 62dB dynamic range applies to spectrum analysis over the range of 10Hz - 100kHz. The -45dB crosstalk spec will certainly limit certain types of amplifier analysis, such as measuring the crosstalk of stereo preamps and amplifiers. In comparison, the relatively inexpensive soundcard I use claims 113dB input dynamic range and -130dB crosstalk at 1kHz.

All this aside, if you can only have one piece of test equipment, and particularly if you dislike buying used gear, the VT can do a lot of work for the money.



 

RE: Another video on Spectral Analysis for audio, posted on May 26, 2016 at 06:45:47
TRUFI
Audiophile

Posts: 622
Location: So. California
Joined: March 16, 2002
 Thanks. I do have a 40 year old Tek scope. I was planning on using the VT for spectrum analysis, THD, IMD measurements. Supposedly it will also function as an LCR meter. Does a lot for the money and I have a spare PC available.

 

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