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Pondering how to choose SimpleP48 resistors, it suddenly occurred to me that we can use the techniques in FETbias.doc so I've updated that in my Files/Ricardo directory.
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It's so obvious with hindsight that I beg yus guy's pardon for my stupidity.? Measuring at 9V is perfect cos we want 5 - 10V
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Mea culpa, mea culpa, mea maxima culpa. |
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Hi Richard,
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Can I even set up the easy test condition of Fig. 1 if my electret is two-lead, for instance, PUI AOM 5024? I then only have access to the drain and to the already internally connected gate and source and I don't know how they are connected internally.
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Also, I'm not clear how this instruction works (or I guess I mean why it works), regardless of whether two- or three-lead:
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Is the 6k8 resistor in the equipment providing the 48 volts? It is standard?
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Sorry, struggling here a bit,
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-John
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On Sat, Sep 28, 2024 at 05:32 PM, John Thaden wrote:
Fig 1 in FETbias.doc is exactly applicable to PUI 5024
Yes.? The 2 x 6k8 is standard for 48V Phantom Power
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I had explored this issue before, but later gave up. I don't know how the perfect bias voltage of 9V for the PUI5024 microphone is generated. However, when connecting the PUI5024 to different devices, the voltage on the two pins is different when using a 6.8k ohm resistor. Later, I chose a 20k ohm potentiometer, rotated it, and measured with a multimeter to find the resistance value that could create a 9V voltage between the two pins when used with my recording device. Then, I bought a fixed resistor based on that value. On Sun, 29 Sept 2024 at 11:54, Richard Lee via <ricardo_lee=yahoo.com@groups.io> wrote:
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For my devices, the Zoom H6 Essential and PUI 5024, I constructed a Simple P48, and the chosen resistor value is 75K. On Sun, 29 Sept 2024 at 12:08, dog hot <zushi000@...> wrote:
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Thank you for the further information, Richard. I surmise then that the short between source and gate shown in Fig 1 is internal to the capsule. I look forward to using this really simple method. -John
On Saturday, September 28, 2024 at 11:51:49 PM CDT, Richard Lee via groups.io <ricardo_lee@...> wrote:
The 5 - 10V is between the terminals on the capsulei ... NOT on the XLR
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The 'new' method obviates messing about with a zillion resistors or pots.
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Richard - thank you for the info and thinking how to make life easier for simple, electronically dumb individuals like me.
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But... (there's always a "but" - this is a rule of the Universe) - the 48V and 9V are only a beautiful, easy approximations.
In practice, as you perfectly well know, this "48V" varies from one recorder to another (usually lower). And the "9V," even in a fresh battery is not equal to 9V.
Therefore, shouldn't we measure and use real voltages in this equation?
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"The Total Resistance has 48 - 9 = 39V"
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Or the differences are so minuscule in the final outcome that they do not matter?
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Cheers |
开云体育For a start, the "9V" in the equation is not cast in bronze. One may argue that 7V or 5V is better than 9V, if only because no FET is equal to another, and noise performance would dictate to go towards the lower side. Before reaching a critical (partially destructive) value, increasing Vgs increases noise (due to the GS junction reverse current). In addition, designing something that requires perfect voltage
source or zero-tolerance components is bad practice. Le 29/09/2024 à 11:53, pmfalcman a
écrit?:
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开云体育A more elaborate answer would take several pages of discussion,
so "yes". Le 29/09/2024 à 15:17, pmfalcman a
écrit?:
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Jerry (and pmfalcman) is (are) of course right.
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By all means measure your P48V and 9V before doing the arithmetic.? Da P48V is specifically important as many so called Prosumer 'P48' devices may be much less.? I ask people to do this in simpleP48.pdf to give tested values for various capsules.
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Please keep sending me these test results for simpleP48.pdf for those (shock horror !!) who are MicBuilding without a multimeter.
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But we are shooting at a broad target; 5 - 10V.? Drawing Fig 6 in FETbias.doc has highlighted the consequences of just using E24 resistors.? It has also prompted me to personally go again for 5V instead of 10V .. something I keep vacillating between. :)
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I have to resist making the circuit more complex to 'cure' its shortcomings.? But then my failing eyesight and deteriorating soldering skills won't let me fit even one extra bit inside a male XLR.
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There's also an even simpler circuit but IMHO, this sacrifices stuff like simpleP48's excellent RFI/EMI immunity etc .. lesser known features that distinguish good mikes from great mikes. |
John Thaden