world's most shielded cheapo USB sound card: 100g copper - Page 1
Forum section: electronics / projects

author: ChristofferB
author_rank: Frequent Contributor
timestamp: January 09, 2020, 08:22:39 pm
content: I'm getting a NIM bin full of nuclear/particle measurement modules!!Hype! Multiple shaping amplifiers, spectroscopy amplifiers, gate stretchers, HV bias etc.I want to mess about with a PMT and some gamma-spectroscopy but it seems the rack is missing the ADC and/or multichannel analyzer. Bummer.There are quite a few different "sound card multichannel analyzer" software packages available for free, and I figured using proffessoonal amplifiers/shapers for all teh low level stuff might make it a pretty decent-ish system until i crack and spend all my money on an actual MCA.I was worried about digital noise from the laptop making its way back so I decided to provide some additional noise reduction measures. I wanted a BNC on the sound card dongle anyway so.. Here is a very copper shielded 10$ USB sound card!Is it going to matter at all? I'm not convinced but at least it looks fancy. The IC foam is a bit silly in this application, the thought was for it to act as an absorber in case some overtones of the digital signalling found a resonance mode in the can.Either way, I'm at least pleased with the visuals--Chris

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: January 09, 2020, 09:20:27 pm
content: I think it looks cool, not sure if that is necessary if your only viewing the audio spectrum though. Why not stick a thermo-electric cooler on it, that way you can minimize the the johnson noise from the resistors! Seriously though it looks a lot more like gear now instead of consumer electronics from china, definatly thinking of doing this for the bling value!

author: magic
author_rank: Super Contributor
timestamp: January 09, 2020, 10:22:43 pm
content: That's some tweaks worthy of a serious audiophile, that piece of anti-static foam thrown inside is the bestBut seriously, "computer noise" usually means ground loops and you can't do much about it without galvanically isolating USB.And speaking of ground, those cheapo cards usually use virtual ground at something like 1.6V. So don't connect their analog I/O "grounds" to a real earth ground while the computer is grounded too.

author: ChristofferB
author_rank: Frequent Contributor
timestamp: January 09, 2020, 10:38:12 pm
content: ..Yeah it went a bit more towards style points than use pointAll I really wanted was a BNC instead of a 3.5mm jack.Good to know with the virtual ground! I'm pretty sure the audio ground was connected to the USB ground and shield though. Something to watch out for.Yeah the foam is completely useless in this setup, but if nothing else it will confuse future me when i open the tin in 10 yearsThe humongous can for the tiny board is mainly so I can re-use the can for other things, and make modifications. A few of the 'sound card MCA' papers I found adds a passive LPF of different kinds at the input. Physicists are rubbish at explaining electronics satisfactorily, though. One of the MCA papers was about the construction of a microcontroller based MCA. The paper had a block diagram, no circuit, no code, and no supporting information..

author: magic
author_rank: Super Contributor
timestamp: January 09, 2020, 11:12:52 pm
content: Quote from: ChristofferB on January 09, 2020, 10:38:12 pmMaybe you found a better one. I had two and both used virtual grounds

author: coromonadalix
author_rank: Super Contributor
timestamp: January 11, 2020, 11:50:51 pm
content: I think the shielding cutted pcb's where overkill, a simple metalized hammond enclosure would have make a good shielding ...But if it get the job done why not

author: eliocor
author_rank: Unknown
timestamp: January 12, 2020, 01:40:05 am
content: Not needed for the abysmal poor response of the sound card!Try to measure its linearity or the response near the Nyquist frequency!!!

author: ChristofferB
author_rank: Frequent Contributor
timestamp: January 13, 2020, 09:33:26 am
content: I'm not shielding the sound card from the world.. in shielding the world from the sound cardit is going to analyze pulse height/shape and other people has gotten that working with some degree of linearity between pulse height and detector energy (detector is a photomultiplier).So here's hoping it will do the job!

author: SeanB
author_rank: Super Contributor
timestamp: January 13, 2020, 07:38:15 pm
content: Funny enough I bought a similar cheap USB audio device, and improved it simply by cutting the USB power trace near the plud, and inserting a LC filter, using some salvaged SMD ferrite filters and some 22uF 10v tantalum capacitors. Got rid of a lot of the noise, as most is coming in via the power line. Mght be wotrth doing it to yours as well, though you have a lot more options for inductor because you are not needing it to fit back in the original plastic housing, though you will want a inductor with high loss over high inductance, to avoid ringing, so probably best to use a few dozen turns of wire through another lossy ferrite bead, and solder the capacitor direct on the old USB plug mountings.

author: trobbins
author_rank: Frequent Contributor
timestamp: January 13, 2020, 09:29:12 pm
content: So is the idea to just acquire a circa 20Hz to 20kHz bandwidth signal for digital processing?If the input has higher frequency noise/signal then you will need to brick wall filter that before it gets to the USB device. Those USB devices can have a phantom power feed which can often be disconnected by removing the appropriate feed resistor. You also need to disable/mute any DAC function, as there is often significant bleed over to the ADC input as frequency increases. The low end can be extended by swapping out the coupling cap for a larger uF part.

author: eliocor
author_rank: Unknown
timestamp: January 14, 2020, 12:38:59 am
content: the frequency response of such USB sound cards is awfu: at 44kHz sampling rate, upper than 7.5÷10kHz is several dB down!When you approach the Nyquist frequency there are LOTS of aliasing products....Nothing changes trying to use a much higher sampling frequency as Theremino does: such USB sound card ALWAYS samples at 44kHz.Several years ago I discussed this problem with the Teremino developers team (IIRC Livio?) and I received NOtechnicalanswers on why they used such high sampling rate if the frequency response and quality of the card was so abysmal!

author: ChristofferB
author_rank: Frequent Contributor
timestamp: January 14, 2020, 01:30:29 am
content: Yeah as I've understood it, the MCA that the theremoni people did was more or less a side project. There is also the 'PRA' free soundcard MCA by a Marek Dolleiser that looks promising. I've seen a demo of that software, notebook mic input plugged directly into the tapped mid-amplifier stage of a handheld scintillation counter giving decent enough spectrums to identify isotopes.https://www.gammaspectacular.com/blue/software-downloads/pra-spectrometry-softwareThe only reason I'm so hung up on the soundcard method is that I want to verify my detector setup actually works before I buy/make/program my own MCA.The frequency response of the sound card is actually not that critical, since I have a shaping amplifier in front of it, making all incoming pulses very similar in peak shape / pulse lenght, and very close to gaussian.Thanks for the insight, though!