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Old 23rd February 2019, 11:48 PM   #1
GerardLardner is offline GerardLardner  Ireland
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Default Microphones

Is there an forum/area where microphones are discussed?


Has anyone tried doing an rf mic, like a Sennheiser MKH? I am aware of Uwe Beis' rf mic page at RF-Condenser Microphone Circuit
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Old 25th February 2019, 11:47 PM   #2
Enzo is online now Enzo  United States
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Are you interested in condenser mics, or does the "rf" mean you want to discuss wireless mics?
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Old 26th February 2019, 12:57 AM   #3
scott wurcer is online now scott wurcer  United States
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Quote:
Originally Posted by Enzo View Post
Are you interested in condenser mics, or does the "rf" mean you want to discuss wireless mics?
No the microphone capsule forms part of a FM circuit where the audio modulates the capacitance of the capsule in an oscillator and the FM is detected by a discriminator. There are no high impedances involved but the transformers are a difficult DIY. This is a rare DIY project.
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Old 26th February 2019, 01:01 AM   #4
GerardLardner is offline GerardLardner  Ireland
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Condenser mics. The "RF" bit means that the capsule is used to modulate an RF system comprising an oscillator (Sennheiser use about 8 MHz in their MKH-series mics) directly connected to an FM demodulator. This is not a wireless mic! Rather it uses a directly-connected FM system to read the motion of the condenser diaphragm.

Advantages: The circuit connected to the condenser capsule is low impedance; it does not require gigaohm-value resistors or high diaphragm voltages. Also, it is low noise and, because of the lack of high diaphragm voltage, inherently tolerant of humid environments. See Sennheiser's explanation at https://assets.sennheiser.com/global...tePaper_en.pdf and John Willett's description in Line Up, June/July 2003, available at Technology of RF Condenser Mics.

The Sennheiser MKH mics are some of the best mics money can buy; but you need quite a lot of it as they are /very/ expensive ($1,300-$2,600). The technology should be amenable to some DIY inventiveness, as Uwe Beis has shown (see link in my original post), but completing such a design is beyond my very limited electronic design skills.

I am hoping I might spark some interest here; perhaps, as many modern industrial instruments use similar technology for reading (often MEMS) sensors, some industrial instrument designer might rise to the challenge.
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Old 26th February 2019, 01:02 AM   #5
GerardLardner is offline GerardLardner  Ireland
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Thanks, Scott. I think you explained it better than I did.
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Old 26th February 2019, 01:54 AM   #6
scott wurcer is online now scott wurcer  United States
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Originally Posted by GerardLardner View Post
Thanks, Scott. I think you explained it better than I did.
You have the right idea, I think the transformers and the fine tuning of this circuit keeps folks away. I have only seen one or two DIY attempts over the years. The conventional approach is easier to understand for most folks I think, and after all there are not a lot of other commercial vendors either. Any patents have expired decades ago.
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Old 26th February 2019, 05:06 AM   #7
PRR is offline PRR  United States
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The capsule can be almost any distance from the head-amp.

I had a Stevens from the late 1950s. The electronics were bigger than a shoe-box. The capsule was hardly bigger than a tie-tack mike, coupled to the box with 20 feet of simple coax.

By the time I got it, it didn't work right, and diagnosis was non-obvious, keeps folks away. By this time JFET-Electret tie-tacks were so cheap the Stevens RF wan't worth fooling with.
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Old 26th February 2019, 06:48 AM   #8
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