Products > Test Equipment
Question: Cheap pure sine wave genertor 1khz?
cncjerry:
I've found that you have to spend a fair amount on a sound card to get anything near the performance of Williams, Wien bridge, etc. First off, the sound card has to be external and then you have USB noise to contend with. You can fix some of that with good cables and opto isolated USB adapters and lifted grounds. But even then, and I've been messing with this stuff for 45yrs, it's tough to find something that will outperform those old lightbulb circuits.
One thing I didn't see was the DSA you are testing? I just bought an HP 3562a DSA and that is good for a boat anchor but the best it will do in range is 120db. It is listed at 80db but there is a way I read someplace to get it to 120db. It must be averaging or something or maybe that was the minimum signal. I've only had it a few days.
One other thing, stop posting all the HP distortion analyzers or all I have to buy one soon. I've wanted one and every time I get it out of my system, someone posts another picture.
Lastly, I was wondering is that I have HP Selective Level meters that are really accurate. I don't know how low they go but I was wondering if I can use one of them for THD testing. I'll have to go back and see if they are flat down to 1khz.
Thanks,
Jerry
cncjerry:
when you are generating sin waves you have to be aware of the large number problem. depending on how long you let that code run, sooner or later you are going to glitch. You need to generate the wave in an array so that the start at zero and the end will perfectly meet and then write the array blocks out. I say blocks because I don't think, and I've not thought about it in a while, you can get a 'perfect' sine wave out of one block at 48k. Here's a simple test. Calculate two 48k blocks generating the code as you did sequentially and then compare block 0 with block 48,000 and on to see if you have the same numbers. Then write the file to disk and plot the spectrum before looping it out the card and back in.
You should also plot your noise floor to see how much junk you have coming from the sound card.
David Hess:
--- Quote from: cncjerry on January 12, 2020, 08:43:34 pm ---I've found that you have to spend a fair amount on a sound card to get anything near the performance of Williams, Wien bridge, etc.
--- End quote ---
No sound card will produce a signal as clean as the second example I gave which was designed for *testing* audio ADCs so necessarily has lower distortion.
MasterT:
I checked out AN67, sorry for my anglaise, but it's the most ridiculous /stupid circuits I've seen in a years. 180 dB, with funny two diodes?
Marco:
It does look like an April fools joke doesn't it ... you can't just have a controlled current source drive current into the overcompensation input of an opamp and not explain what the hell that's supposed to be doing.
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