EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: zouwi on December 20, 2021, 04:10:28 pm
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Hi!
I apologise if this new therad is against good manners, but after lurking for a few months and extensive searching I didn't find really info for tools on audio work specifically.
My current situation is that I have a basic multimeter (Fluke 113) and el-cheapo chinese 12MHz 8ch logic analyzer and pretty good collection of pro-audio stuff (audio interfaces, computers, software, actual pro-audio gear, etc). I used to have a 50MHz tektronix oscilloscope on a long term lease, but that has returned to it's owner for now. I have started working on my Master's thesis on audio and signal processing, which includes all kinds of things from analog to bluetooth. I have good experience on analog audio, reasonable experience in digital and embedded, but things like ultra-portable embedded audio (e.g. new Qualcomm bluetooth-audio chips), long digital transfer lines and bluetooth radio are new to me. I have something available from university, but obviously acoustics department doesn't have 5GHz oscilloscopes or anything like that. Reason for buying things for myself is that I would like to have at least some tools, so if I end up working with those things in future I would already have equipment to produce prototypes.
I think that I would need at least a good benchtop multimeter, logic analyzer and oscilloscope to deal with analog and digital audio (please correct me on this if I miss something opbvious), but for the bluetooth I'm completely out of knowledge.
A local dealer for used gear has a Keithley 2015 with dim display for under 500€, so that seems like a no-brainer. It will likely need re-capping, which isn't that much of a problem for me, and later possibly attempts to re-vitalize the display or completely swapping it out for oled if the original spare is unavailable or prohibitively expensive. I don't think I can get this kind of performance for same price in any other way. It doesn't measure cap sizes or ESR, but a 20€ cheap component tester should be good enough for those. Measurements for capacitor leak currents should be possible with constructing a low-noise amp with current gain of 40dB or so, and measure that. I don't really need the audio measurement functions from the Keithley, so if there is some other DMM I should consider, please tell me.
For logic analyzer, I have been thinking Saleae Logic Pro 16. I have been really impressed with their first gen product and overall software (reasonably easy to export decoded data and analyze that further in Matlab) and those 16 inputs in analog mode would be really nice for debugging and fixing analog audio devices (like finding bad caps on old mixing console channel strip). A mixed signal oscilloscope could probably also work, although it would have fewer analog channels and more difficulty in exporting and analyzing decoded signals.
For oscilloscope I don't really know what to do. If the Saleae isn't that much good of a deal it should be mixed signal device, I don't know if it should have a function generator and I don't know what kind of performance I need to verify long digital signal lines. Highest frequency digital audio line I can think of is 8ch * 32bits * 192kHz = 49,2Mbits/sec TDM signal, so at least 200MHz to see if nothing odd (reflections, distortions, anything else?) is happening on data or clock lines, preferrably 350MHz or more. Right now I would need to check 2ch * 32bits * 384kHz = 25Mbits/s I2S = 50MHz signal integrity, although I hope our lab has good enough scope for that. (That device is for ultrasound research, I don't need advice on choosing samplerates.)
For bluetooth I'm even more out of knowledge. I think that the easiest way to go would be to use a chip antenna, but I have no idea how those need their related caps and inductors decided. I don't really need more performance than it to work for range of 2 meters or so, but I think I would still need to have at least slight idea on antenna performance. Would I manage with a cheap (under 100€) chinese VNA? I don't need to go analyzing the BT traffic, it is taken care by the embedded device, but I need some kind of confirmation that my device at least should get some signal through in both directions.
Now the difficult part: I would prefer to get the oscilloscope for under 1000€ or 1500€ if it also works as logic analyzer and I don't have money for anything fancy for 2,5GHz frequencies. The cheapest oscilloscope from the dealer with the Keithley is over 12k, so just buying something from them isn't unfortunately possible. Shipping from US to Finland (also currently from UK) is expensive and difficult, so I'm pretty much limited to EU area for used gear.
Thanks in advance, and my apologies if this thread is on wrong area or otherwise against policy.