Sort of, but like the complete opposite. But I'd rather let the designer himself explain.
OPEN SOURCE DIY Mic Project - ORS 87 - Stripped Down u87
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Sort of, but like the complete opposite. But I'd rather let the designer himself explain.
homero.leal
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Direct quote from LNPrimer.doc, by @ricardo The doc can be found on the MicBuilders forum.
"PCB layout is critical for low noise. The first rule is to be very clear what your earths are doing. I always define 3 earths; Clean, Dirty and Chassis. I won’t talk about evil Digital earths but see the above link on www.planetanalog.com Consider carefully what you are doing when you connect anything to an earth. If you connect supply decoupling capacitors to an earth line, you make it Dirty. In our simple circuit, Clean earth is used ONLY for input / output earths and feedback components. The 10k input resistor is taken to BP so this line must be treated like Clean earth. BP is joined to Clean earth via a single 47u right at the input sockets. Dirty earth carries our supply decoupling currents. The 3 earths are joined ONLY at one point, at the output in our simple circuit. Output current does not upset the Clean input and feedback paths; a common source of instability. Some of you will recognise this as similar to "Star Point" earthing in power amplifiers."
"PCB layout is critical for low noise. The first rule is to be very clear what your earths are doing. I always define 3 earths; Clean, Dirty and Chassis. I won’t talk about evil Digital earths but see the above link on www.planetanalog.com Consider carefully what you are doing when you connect anything to an earth. If you connect supply decoupling capacitors to an earth line, you make it Dirty. In our simple circuit, Clean earth is used ONLY for input / output earths and feedback components. The 10k input resistor is taken to BP so this line must be treated like Clean earth. BP is joined to Clean earth via a single 47u right at the input sockets. Dirty earth carries our supply decoupling currents. The 3 earths are joined ONLY at one point, at the output in our simple circuit. Output current does not upset the Clean input and feedback paths; a common source of instability. Some of you will recognise this as similar to "Star Point" earthing in power amplifiers."
That may very well apply to line-level circuits powered from the mains grid, that interact with other equipment powered from the mains grid. Some appropriate context for that quote would have helped..?
Found @ricardo 's quote on this forum as well, but as expected from the wording, it refers to preamplifiers, NOT microphone impedance converters...
https://groupdiy.com/threads/ina134-and-drv134-supply-bypassing.56079/post-715735
Unless you have special mic cables that have a separate shield that connects ONLY to the mic chassis, and the circuit ground of the circuitry connects ONLY to XLR pin 1.
As far as I'm concerned, a phantom-powered microphone might as well be a "floating" system, since it ONLY connects to the preamp you plug it into (tube mics could have a ground-lift on the output XLR, but that's a different issue).
Really no idea how and what "ground loops" you can achieve inside a mic, but i haven't managed that yet, despite my "careless" and "unwise" use of ground planes
PS. I would also slightly object to there being multiple "earths" there - i've been taught "earth" is (strictly) mains earth; anything else is a (circuit) ground. If only to try to avoid confusion...
Found @ricardo 's quote on this forum as well, but as expected from the wording, it refers to preamplifiers, NOT microphone impedance converters...
https://groupdiy.com/threads/ina134-and-drv134-supply-bypassing.56079/post-715735
Unless you have special mic cables that have a separate shield that connects ONLY to the mic chassis, and the circuit ground of the circuitry connects ONLY to XLR pin 1.
As far as I'm concerned, a phantom-powered microphone might as well be a "floating" system, since it ONLY connects to the preamp you plug it into (tube mics could have a ground-lift on the output XLR, but that's a different issue).
Really no idea how and what "ground loops" you can achieve inside a mic, but i haven't managed that yet, despite my "careless" and "unwise" use of ground planes
PS. I would also slightly object to there being multiple "earths" there - i've been taught "earth" is (strictly) mains earth; anything else is a (circuit) ground. If only to try to avoid confusion...
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