I recently started shopping for a spectrum analyzer for my diyAudio builds. Everything I found works in the Gigahertz range. Many start at 9kHz. But I know people use spec analyzers on this site. can anyone recommend a specific make and model that is inexpensive and works in the 10Hz to 40kHz range?
Room Equalization Wizard software on a computer with a soundcard would work. Check out this thread:
You have several devices that will give you FFT's. Audio Precision systems & similar will give you 10Hz to 1MHz. Many DSO will get you good FFT . Some sound cards & software will also do FFT, however BW may be a big limiting factor in many sound cards.
Thank you both. I would love to get one of the Audio Precision systems but I'm not willing to pay what those things cost.
The REW software looks like the way to go. I already have a Presonus Studio 24c for measuring speakers. I just need to buy some new cables to figure out how to apply it to an amplifier or preamp.
The REW software looks like the way to go. I already have a Presonus Studio 24c for measuring speakers. I just need to buy some new cables to figure out how to apply it to an amplifier or preamp.
Rew is great, lots of features. Especially for speakers.
Specialized for electronics, amps, preamps is RightMark Audio Analyzer. I use both, rew and rightmart, preffer rew for speakers, rightmark for electronics.
https://audio.rightmark.org/index_new.shtml
Specialized for electronics, amps, preamps is RightMark Audio Analyzer. I use both, rew and rightmart, preffer rew for speakers, rightmark for electronics.
https://audio.rightmark.org/index_new.shtml
For audio you want a audio signal analyzer or dynamic signal analyzer (aka FFT analyzer), not an (RF) spectrum analyzer. RF spectrum analyzers have lots of distortion in their front ends. I mean lots. Even -35dB IMD is pretty good for RF... For audio we want -100dB or even better, that simply cannot be achieved at RF.
DSO's have high distortion too, they are designed for 100's of MHz, and most are only 8 bit ADCs anyway.
But you can do this with software from a quality PC soundcard.
My favorite affordable device is the QA403, well affordable compared to Audio Precision at least!
The QA40x is far and away the best option without spending big bucks. Been there, done that. Don't try to use a sound card / audio interface. Yes, it can be done, but calibrating it is a pain, and they're really too fragile for working on amplifiers. A few years ago, I started trying to design a low-distortion front-end for use with a sound card. At the time, you couldn't get any of the QA40x analyzers (chip shortages). As instrumentation projects go, it's a significant pain in the backside, and ultimately I couldn't do it for significantly less than QuantAsylum.
If you're measuring speakers and rooms, get yourself a decent audio interface (most of them are good enough) and your preferred software (I use ARTA).
I will caution you, even if you do find a spectrum analyzer that goes down to 10 Hz (they exist - IIRC HP made a 10 Hz to 40 MHz model), they're fragile and extremely difficult to repair. It's not the right tool for this job.
If you're measuring speakers and rooms, get yourself a decent audio interface (most of them are good enough) and your preferred software (I use ARTA).
I will caution you, even if you do find a spectrum analyzer that goes down to 10 Hz (they exist - IIRC HP made a 10 Hz to 40 MHz model), they're fragile and extremely difficult to repair. It's not the right tool for this job.
What are you looking to measure?
I've used my 9 kHz - 1.8 GHz spectrum analyzer for looking at oscillation in audio amplifiers. That's handy. But I've done that exactly once with a headphone amp that oscillated in the 100-200 MHz range. I bought the analyzer for 10 cents on the dollar at an employee surplus sale where I used to work.
Do note that RF spectrum analyzers do NOT like DC on their inputs. Even small DC voltages wreck the RF input. Also note that many of them have limited dynamic range. 80 dB is common. Some of the newer ones are a bit better, but are also a few $k to start for a cheap one.
If you're looking to measure audio spectra, so, say 20 Hz to 20 kHz or maybe upwards of 100 kHz, you're better off getting an audio analyzer such as the QA403 already mentioned. That's $600 well spent. I compared it to the APx555 here: https://neurochrome.com/pages/measuring-distortion-on-the-cheap
If, on the other hand, you're wanting to look at infrasonic frequencies, so DC to 20 Hz, you're better off with a dynamic signal analyzer such as the HP 3562A or 3563A. They measure down to 64 µHz. The AP won't do that even with the inputs DC coupled. There's a more modern version of those analyzers. I forget the model number. It's pretty expensive on the used market and doesn't do much the older analyzers don't, except it has a (now useless) 3.5" floppy drive.
If you really want to go cheap and measure audio, get a refurbished third generation Focusrite Scarlett Solo. It'll set you back less than $100. It's not the most resolving, but with nearly 100 dB dynamic range at its sweet spot it's really not bad. Do note, however, that by the time you add all the cables, adapters, and attenuators you need to use a sound card as an (uncalibrated!) audio spectrum analyzer, you're well past half the cost of a QA403, so if you're even moderately serious about it, I'd go for the QA403. Then you get a calibrated setup right out of the box.
Tom
I've used my 9 kHz - 1.8 GHz spectrum analyzer for looking at oscillation in audio amplifiers. That's handy. But I've done that exactly once with a headphone amp that oscillated in the 100-200 MHz range. I bought the analyzer for 10 cents on the dollar at an employee surplus sale where I used to work.
Do note that RF spectrum analyzers do NOT like DC on their inputs. Even small DC voltages wreck the RF input. Also note that many of them have limited dynamic range. 80 dB is common. Some of the newer ones are a bit better, but are also a few $k to start for a cheap one.
If you're looking to measure audio spectra, so, say 20 Hz to 20 kHz or maybe upwards of 100 kHz, you're better off getting an audio analyzer such as the QA403 already mentioned. That's $600 well spent. I compared it to the APx555 here: https://neurochrome.com/pages/measuring-distortion-on-the-cheap
If, on the other hand, you're wanting to look at infrasonic frequencies, so DC to 20 Hz, you're better off with a dynamic signal analyzer such as the HP 3562A or 3563A. They measure down to 64 µHz. The AP won't do that even with the inputs DC coupled. There's a more modern version of those analyzers. I forget the model number. It's pretty expensive on the used market and doesn't do much the older analyzers don't, except it has a (now useless) 3.5" floppy drive.
If you really want to go cheap and measure audio, get a refurbished third generation Focusrite Scarlett Solo. It'll set you back less than $100. It's not the most resolving, but with nearly 100 dB dynamic range at its sweet spot it's really not bad. Do note, however, that by the time you add all the cables, adapters, and attenuators you need to use a sound card as an (uncalibrated!) audio spectrum analyzer, you're well past half the cost of a QA403, so if you're even moderately serious about it, I'd go for the QA403. Then you get a calibrated setup right out of the box.
Tom
The QA403 is extremely affordable by test equipment standards. And you get a lot of performance for that $600. But I do understand that $600 is a lot to spend on a tool you'll use sporadically for a hobby.
Tom
That should be the HP 35660A and 35665A. They both work from DC (down to 244 or 122 uHz) to 102.4 / 51.4 kHz (1ch/2ch). There are kits converting the 3.5" floppy into SD card reader. Both are pretty well documented and servisible, full options firmware/ROM available online.
HP 36570A has 4ch, discontinued in 2018.
Would you happen to have a link to one of those? The ones I see all have USB I/O. I'm thinking those analyzers predate USB.
You can probably get at the data through GPIB. That wouldn't be the end of the world.
Tom
The analyzer I was thinking of is the HP/Agilent/Keysight 35670A: https://www.keysight.com/ca/en/product/35670A/fft-dynamic-signal-analyzer-dc1024-khz.html
Tom
Tom
Sure! I'm also posting everything I've found so far regarding 35660/5A, since they seem to share a lot in common being the same family. Hope they help.
HP / Agilent 35665A and 35670A Floppy Drive Emulator Kits
https://glkinst.com/test-equipment/
Plotting to PC, Options (EEPROM), power supplies, etc
http://btbm.ch/hp-35665a-plot-print-to-pc/
https://btbm.ch/hp-35665a-plot-to-pc-directly-from-gpib/
https://btbm.ch/hp-35665a-all-options/
https://btbm.ch/hp-instrument/
https://btbm.ch/hp-35665a-keyboard/
https://btbm.ch/hp35665a-power-supply-repair/
https://btbm.ch/hp-35665a-power-supply-repair-no-2-trw-p-n-095-10097-hp-p-n-35672-67501/
Service manual and other documents
https://www.ko4bb.com/getsimple/ind...nt_Keysight/HP_35665A_Dynamic_Signal_Analyzer
(The complete 35665A service manual only came out recently these past few years. SM is mostly board level only, but at least it's now complete with all calibration details. For component level detail, it can be read in conjunction with 35660A SM)
Misc documents, SDF file format
https://heartfx.net/dsa.html
LCD screen mod (for other HP instruments)
http://www.simmconnlabs.com/1401/index.html
Btw Tom, I've been reading a lot on QA403, thinking about getting one, your writings and video help a lot! Thanks!
That post is a great resource. Thank you for sharing. The KE5FX GPIB Toolkit linked to on one of the pages is excellent too: http://www.ke5fx.com/gpib/readme.htm
Tom
Tom