if you're happy with a pc based solution try pete milletts:
Test & Measurement interface for Soundcard
i just built mine, but its not tested yet
Test & Measurement interface for Soundcard
i just built mine, but its not tested yet
What do you intend to measure with the spec an?
A spec an is useful for figuring out the composition of a frequency spectrum. So, for example, if the distortion of an amp is mostly even order or odd order harmonics. It's also useful for debugging hum issues.
It can be used to measure THD, though, only the fancier spec an's have a THD function. For measuring THD, I find that a dedicated distortion analyzer works the best.
What to look for in a (used) spec an:
- Does it work?
- Is the screen bright and in focus?
- Frequency range
- Minimum and maximum frequency span
- Resolution bandwidth
- Noise floor
- Input voltage range(s)
- Input over-voltage protection
Note that an external computer sound card with a sound card interface (see the one made by Pete Millett as an example) can be a pretty darn decent audio spec an.
On my website, I have a write-up on distortion measurement equipment. You may want to take a look at it.
~Tom
A spec an is useful for figuring out the composition of a frequency spectrum. So, for example, if the distortion of an amp is mostly even order or odd order harmonics. It's also useful for debugging hum issues.
It can be used to measure THD, though, only the fancier spec an's have a THD function. For measuring THD, I find that a dedicated distortion analyzer works the best.
What to look for in a (used) spec an:
- Does it work?
- Is the screen bright and in focus?
- Frequency range
- Minimum and maximum frequency span
- Resolution bandwidth
- Noise floor
- Input voltage range(s)
- Input over-voltage protection
Note that an external computer sound card with a sound card interface (see the one made by Pete Millett as an example) can be a pretty darn decent audio spec an.
On my website, I have a write-up on distortion measurement equipment. You may want to take a look at it.
~Tom
The PC sound card based analyzers work quite well for audio analysis (especially 24 bit ones), but are typically limited to just the near audio band.
They are fast too and dual channel (useful for comparing input to output in real time). And storing spectrums are easy on the PC. You can do special tracking oscillator and analyser methods too for filter analysis.
A more conventional swept filter spectrum analyzer will typically be slower, but maybe higher resolution, and will provide wide band analysis (like say 5 MHz for a 7L5 Tek scope plug in). This is useful for finding HF resonances (NFDBK stability checking) or parasitic oscillations above the audio band. (although one would want more like several hundred MHz capability for that) Some units will have an optional or built in tracking oscillator for filter analysis. If you are using any kind of switchmode power supply electronics in your build or system, then a several hundred MHz unit will be needed to check for EMI compliance and interference effects.
With either kind, you need to be careful about overloading the input to the analyzer/sound card. Easy to blow them up, and costly.
They are fast too and dual channel (useful for comparing input to output in real time). And storing spectrums are easy on the PC. You can do special tracking oscillator and analyser methods too for filter analysis.
A more conventional swept filter spectrum analyzer will typically be slower, but maybe higher resolution, and will provide wide band analysis (like say 5 MHz for a 7L5 Tek scope plug in). This is useful for finding HF resonances (NFDBK stability checking) or parasitic oscillations above the audio band. (although one would want more like several hundred MHz capability for that) Some units will have an optional or built in tracking oscillator for filter analysis. If you are using any kind of switchmode power supply electronics in your build or system, then a several hundred MHz unit will be needed to check for EMI compliance and interference effects.
With either kind, you need to be careful about overloading the input to the analyzer/sound card. Easy to blow them up, and costly.
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DL4YHF's Audio Spectrum Analyser
Get Speclab.
It's free. The finest piece of amature software I've ever seen. Absolutely superb!
Doc
Get Speclab.
It's free. The finest piece of amature software I've ever seen. Absolutely superb!
Doc
An audio spectrum analyzer is fairly expensive. I paid $800 for mine (early 1980'ies vintage). If you don't know what to do with it, I suggest using a computer sound card until a need for a dedicated instrument arises.
"Check performance" is not very specific. You can check performance with an oscilloscope and a voltmeter. Which parameters are you looking to measure with the spec an? Don't expect to be able to measure THD below 0.01 % on 1980'ies vintage spec an's. My HP 8903A distortion analyzer measures down to 0.003 %. If you want lower, you'll be looking at the $50k Audio Precision SYS-2700, AP SYS-1, or similar.
If you have money burning holes in your pockets, look at any of the Agilent audio spectrum analyzers. They're probably in the $30k~$50k range. If you don't have that much money burning holes in your pockets, I suggest looking at an HP 3562A Dynamic Signal Analyzer. It's a precision audio-range signal source plus an audio spectrum analyzer (FFT based). That'll set you back around $1k maybe less if you happen to find a good deal, maybe $2k~$3k for a calibrated unit. There is also a dedicated audio spec an in the HP 35xx-series. I forget its number. As you can see on my website (deep link in my previous post), there's also the HP 3581A which can be used with an XY plotter as a spec an. There's also the HP 3580 which is the same 1970'ies vintage as the 3581. Even older gear like HP 181 (I think it is) might work as well, though, I forget its lower frequency limit. That's in the $400-ish range.
Tektronix also has some offerings that went into the rack-based oscilloscope boxes.
Or you could spend $100~$200 on a solid external USB/FireWire sound card and get going that way. TrueRTA is a pretty good software package as far as I can tell. A soundcard-based solution does have some shortcomings but is pretty cost effective.
~Tom
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That would be the HP 3580A. I have used one of these for years and they are great for sweeping filters. They top out at 50KHz, but the adaptive sweep and 1Hz bandwidth along with the built in tracking generator fills the bill very nicely. Unfortunately none of the older HP analyzers mentioned are supported by mother. And they are not easy instruments to support without scrap units. Some of the parts inside are matched and selected by HP making upkeep difficult if they fail.
Attachments
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The one I had in mind was the HP 3561A dynamic signal analyzer. I think it's basically a one-channel version of the 3562A analyzer portion. So no source. That's a bit less than a 3562A, but you can't measure THD without a precision (low THD) source so I don't find it all that useful by it self. But it can be used as a spec an....
The 3580, 3581 are easy to fix from a circuit perspective. There's nothing more complicated than 7400-series logic as I recall. But as you say, many of the parts were selected and matched by HP and are hard to come by these days.
~Tom
...and $0 to about $250 or so for an interface to attenuate the amp output down to 2V or so, so you don't smoke the input of the sound card. The $0 solution is a simple voltage divider from your scrap box across your 8R load resistor to feed the soundcard what it needs and the $250 or so is for Pete Milletts sound card interface which has a scalable attenuator, high input R, low output R (buffer), an accurate AC voltmeter, and a few other nifty features.
I've recently tried the $0 solution above, but it doesn't %$^#!!! work for some reason. I have a voltage divider consisting of a 470R and 500R pot across an 8R load resistor. Pot wiper out to soundcard line in.
Works great at variably attenuating the amp output (looking at the sine wave on my scope) until I connect it to the sound card input........
And then you have a ground loop, or in case of a bridged amp, a short circuit between output and ground.
Hi ,
I use a software solution with speclab and an external soundblaster card with a homebrew testfixture to connect devices under test.
And I also have older hardware solutions. An spectrum analyzer from "Spectralab" model SD330, probably one of the ever first made spectrum analyzeres at all. This piece of equipment is made in 1977. I got it for few euros at my local scrapyard. The other one is an HP3580. I came across it on a ham fair. Sticker on it says its former geman telecom gear.
The properties between the older hardware and the modern software solution are miles apart from each other . The quality of the measures depends mainly on the soundcard.
Get speclab and you will happy with it.
regards
Wolfgang
Hi , it is absolute neccessary to insert an isolation transformer if you like to test in- or output on floated potential e.g bridged outputs or electronically balanced inputs. The mains input of the device under test shoud feed via an isolation power transformer. Ground loops can lead to self oscillation which are dangerous for power stages . Isolation leakage currents can turn your soundcard and the computer easily into worthless scrap
That means your test setup shold be meticulous and clean, doblecheck before turn it on.
73
Wolfgang
That's what I have been using for 6 or 8 years now. I bought one of Petes interfaces but never had the time to build it.
Some HP test equipment used their proprietary SOS (Silicon On Saphire) microprocessors in the early 1980's. These chips are UNOBTAINIUM today and they do fail. I bought a HP3585A spectrum analyzer at a hamfest for $100 in non-functioning condition. I soon found out why it was $100....dead chip. The CRT's are hard to get too.
I think the HP8903A audio analyzer used an SOS chip. I am not sure since I have never seen one of them fail. I worked in the cal lab of a large manufacturing plant where we had hundreds of 8903A's
OK ....question can this DL4YHF's Audio Spectrum Analyser be used for THD measure ?
or ...is there a tutorial on how to use this tool in audio frequencies
or ...is there a tutorial on how to use this tool in audio frequencies
Note that for THD analysis you would need to be able to measure the harmonics. If a soundcard-based solution can't see frequencies above 22 kHz, then THD measurement capabilities would be quite limited. For example, THD-20 (i.e. using a 20 kHz tone) would be impossible. Even THD for 1 kHz would only be able to use four harmonics. Faster sampling than 44 kHz should enable higher frequencies to be utilized.
If you do look for a "real" spectrum analyzer, make sure that you pay attention to the low-frequency specs. Most of them are for RF and don't go below 10 MHz.
If you do look for a "real" spectrum analyzer, make sure that you pay attention to the low-frequency specs. Most of them are for RF and don't go below 10 MHz.
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I wish I could find a good open-source software based analyzer that also supported USB/Firewire (maybe wireless?) input sources, and ran native on OS X (maybe X11) and Linux (why not the iPad too?). I prefer to avoid Windows, but as a last resort might do it in a virtual machine under Virtual Box (open source and free to individuals virtualbox.org ). Then the whole PC installation can be easily copied as a drive file to a USB flash drive or something, for easy deletion and replacement when it gets infected. If one is simply doing repairs, most gross faults are easy to see with the triangular wave from a function generator, and a scope. The distortion from simple higher distortion low/no feedback tube amps is often visible. A distortion analyzer with a scope on the output is very revealing if one understands what it is doing. Full hardware-based spectrum analyzers will generally require either good scrounging/repairing skills or plenty of money, sometimes both. Test equipment is addicting, and with many finding some particular use they like each instrument for. It is easy to want many types. Many have been unsupported for decades and it may take buying another unit to have parts. At one point I was looking at buying another analyzer for the knobs. Really. But it had broken knobs too. Some get brittle and fall apart. Some of the plug-in analyzers are hard to test without extender cards. Those are rare and sometimes sell for as much or more than an analyzer. Digging through the manuals and museum type sites one can find app notes for using spectrum analyzers. Those can provide insight into what they can do and how they work. There are many uses for r.f. analyzers in ham radio. The 7L5 is not only good for audio, but can tell you when an A.M. transmitter is occupying too much bandwidth. Trying to pick up a weak specialized satellite signal that requires nulling the cross-polarized interference from adjacent transponders is easy when watching to null the interference on an analyzer. If you're trying to pick up a distant FM station and want to filter out a strong local station that overloads your preamp, an analyzer will show what's going on. Are you hearing multiple AM or FM signals jumbled together on some frequencies and want to know if its distortion in your radio or cross talk at the transmitter site? Time for a spectrum analyzer. It's an expensive tool to help aim a TV antenna, but it works for that too. Often many tools can be used for a particular task. My HP 300A Harmonic Wave Analyzer is tunable to measure one harmonic at a time. Those came out in 1948, it has a wood cabinet. The 330B tube type analyzers have been frequently used as movie props. One was in the Battlestar Galactica series. Studying designs of test equipment is educational. For a while I felt like I was about the only one that paid attention to intermodulation from the voltage swing of one signal affecting the gain and phase of other signals, and the feedback loop response, by modulating the junction capacitance. It hit me when I noted overshoot that changed with voltage level. Much later I saw that Tektronix was using varactor diodes in emitter circuits to vary high frequency correction with voltage level (compensating for elsewhere in the circuit). Besides the utility, once one digs into test gear and sees all of the level of innovation, its easy to have a love of gear as a fine art form. Another place to broaden horizons is ham radio. Many might enjoy many aspects of ham radio, or even just articles written for it. All the back issues of "Ham Radio" magazine are available at archive.org. I think they even had an article on building a spectrum analyzer. One of the issues had an ad for the assets of a tube factory being sold off, with descriptions of the equipment. Fascinating history buried in strange places.