The arguments over cheap scopes will never end. They are cheap, they have compromises. Depending on your application you can live with the compromises or not. Same if its a Keysight, Tektronix or LeCroy. The compromises are not deal killers for most audio applications. And for $100-$150 you can get a lot of work done. I worked with a group designing microprocessors and memory chips who only had 4 channel 50 MHz scopes. Somehow we managed.
I’ll jump on in here… I was looking at cheap scopes just a little bit ago. Right now I’m eyeing an Agilent DSO3102A. It’s got good specs, does FFTs which is important for me, and costs less than $200. I was also looking at an HP 54645A for a similar price, but it’s older and the sample rate isn’t as good.
I would not be inclined to buy an early DSO. Too complex a device for what it can do and those are big and power hungry. Scopes are going down the computer price/performance curve. A Siglent or Rigol would be a current good choice given both performance and quality, but you will be into it for over $300.
I have a Siglent (and 8 Tektronix) but I have found these both to be quite useable and pretty cheap:
https://www.amazon.com/Portable-Osc...ld=1&keywords=DSO1511E+&qid=1633495892&sr=8-3 $118 at Amazon or cheaper from China
and this https://www.amazon.com/YEAPOOK-ADS1...449a8&pd_rd_wg=uh4ul&pd_rd_i=B08L3FRKYF&psc=1 for around $160. They both will run on internal batteries which is great. And they are both more useful than they look. Neither would replace the Siglent (or the Tek 7854) but for convenience they are unbeatable.
I have a Siglent (and 8 Tektronix) but I have found these both to be quite useable and pretty cheap:
https://www.amazon.com/Portable-Osc...ld=1&keywords=DSO1511E+&qid=1633495892&sr=8-3 $118 at Amazon or cheaper from China
and this https://www.amazon.com/YEAPOOK-ADS1...449a8&pd_rd_wg=uh4ul&pd_rd_i=B08L3FRKYF&psc=1 for around $160. They both will run on internal batteries which is great. And they are both more useful than they look. Neither would replace the Siglent (or the Tek 7854) but for convenience they are unbeatable.
Now that is THE project indeed, hats off to the developer. His repository is packed with extremely useful info, from schematics, FPGA stuff, reverse engineering stuff, linux scope app source, even embedded linux build help. A truly unique source of information. Thanks for pointing it out here.
But if you try to do FFTs with an 8 bit scope you will very quickly realize it is pretty useless for audio.
With 8 bits, you have 48dB range, at best. That's just below 1%.
For any serious FFT (meaning for distortion measurement in audio) you really need something dedicated, like a $ 50 soundcard
.Jan
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Which means having flexible bandwidth limiting, since you don't care about the noise between 20kHz and 100MHz for audio, usually.... 1k resistor puts out 40µV rms upto 100MHz bandwidth but only 0.6µV rms between 20 and 20kHz.
With a 100MHz front-end without bandwidth limiting you may see far more noise than you expect. My old Rigol 'scope had adjustable bandwidth limiting and it was very handy for low bandwidth stuff like audio. My newer Siglent only has 20MHz limiting alas.
20Mhz is more than enough. The oscilloscope need to see more over 20Khz to be able to see parasitic oscillations that is possible to appear in amplifiers. I "measured" over 5Mhz oscillations in one audio amplifier.
If you want to see only 20Hz to 20Khz better use a quality PC audio board and you will have better noise performance and much more better resolutions (min 24 bits comparing with 8 bits - 12bits).
