Electret microphone wiring
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Hi all,
I am trying to use a cheap computer microphone in my K3, front 8 pin connector. I have some doubts that I would like to solve before making a mistake: 1- Can I use pin 1 directly atached to the electret capsule and set bias in config:MIC SEL? Or should I use also some kind of resistor/condenser arrangement to the 8V DC pin6? 2- For GND: shoul I use pin 7, pin 8 or both pins? Thank you very much in advance. Ramiro. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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<<<<I am trying to use a cheap computer microphone in my K3,
front 8 pin connector. I have some doubts that I would like to solve before making a mistake: 1- Can I use pin 1 directly atached to the electret capsule and set bias in config:MIC SEL? Or should I use also some kind of resistor/condenser arrangement to the 8V DC pin6? 2- For GND: shoul I use pin 7, pin 8 or both pins?>>>> I just went through that. My Sennheiser headset now works fine using internal settings for bias. Pin 7 and 8 are the same connection point. I do not believe it is best that they are the same, in my unprofessional opinion one should be a shield ground and one an audio ground, but they are the same. I had to modify my audio input grounding to cure RFI. My headset has a long cord, and when I would stretch the cord I would get bad RFI with my yagi stacks pointed back at my house. Elecraft has a mod for this, but I changed more. I soldered the wire around the mic connector shell to the connector shell, and I grounded the circuit board pin 7 and 8 via a copper foil that grounds under the cabinet screw in that corner. Now I absolutely no RFI into the audio no matter what I do, and with the very long cord all stretched out like an antenna! The Elecraft mod was an improvement, but the copper foil was a total cure for me. 73 Tom ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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On Fri, 23 Apr 2010 06:04:26 -0400, Tom W8JI wrote:
>Pin 7 and 8 are the same connection point. The ONLY proper connection point for a cable shield is the shielding enclosure. Doing anything else creates what is known in the audio world as a "pin 1 problem," whereby shield current (RF or baseband power- related buzz) can flow on interior "ground buss" wiring, couple into gain stages, and be detected and/or amplified. Since the AES charges non-members for Standards, I've put technical discussions of that Standard, for which I led the writing group, on my website. http://audiosystemsgroup.com/publish.htm IF the cable shield is separate from both signal conductors (that is, hot and return, as in a balanced mic), it's fine to separate return and shield. But if there's only the shield, it MUST go to the chassis. For many years, I didn't own a dedicated ham mic other than a PTT that came with a radio, so I grabbed an RE16 from my stock of recording mics and used that. It worked fine with suitable EQ as long as I made sure that the cable shield went to the chassis, but a rig with a pin 1 problem could experience RFI. Several years ago, I acquired an FT1000MP, and got reports of RF feedback on 75M and 15M. I ran the pin 1 susceptibility test that's described in one of the AES papers that's on my website on that mic connector, and found strong susceptibility with two peaks -- one a broad one that peaked just below 5 MHz and the second that peaked just below 21 MHz. Seven turns of the mic cable around a #31 2.4-in o.d. toroid killed the RFI. MOST ham rigs come with pin 1 problems -- the MP and K3 are not alone. It has taken radio circuit designers a long time to realize that someone outside their own limited world might know something more about RFI than they do, or to even read beyond their world. The guys who worked with me on AES EMC Standards all have serious RF backgrounds. To get back to the original question, the K3 has EXCELLENT good support for unbalanced electret mics. All that is needed is to connect the mic output to the mic input and turn on the bias via the menu. Inside the radio there's a 5.6K resistor from DC+ to the mic output. And there's enough TXEQ to accommodate the frequency response of any decent mic. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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<<<IF the cable shield is separate from both signal
conductors (that is, hot and return, as in a balanced mic), it's fine to separate return and shield. But if there's only the shield, it MUST go to the chassis. >>> If one "ground" pin was dedicated to the chassis or cabinet ground, the other pin could be run through RF bypasses to the "cold" side of the audio input PC board. Then, in the case of a mic with an isolated ground return inside the shield, or even a balanced mic or unbalanced mic, the audio return could go to that pin. The shield could always go to the cabinet or chassis with the lowest possible impedance. No chokes, no bypasses. This is the same place the mic connector shell should go. If the mic had only the shield for an audio return, the shield and audio return pins could be bonded at the connector. This would be a simple solution that would cover all bases. For some reason this is an age old problem with Ham gear. Early tube gear used the case as a ground, but for some reason when the digital engineers got involved grounds started getting messed up. This is true for lightning grounds also. For example I did an antenna switching controller and made the chassis the common point for all grounds. The fellow writing the firmware did a whole new layout on his own where he isolated the digital and signal grounds. The result was a unit that failed CE testing for ESD between ports, and had significantly more RF out on leads from the clock. Strong RF would just kill the thing. I had a similar problem with a VOMAX speech processor. The RF power supply decoupling was on a single toroid and both negative and positive supply leads passed through it as a bifilar winding. While this provided reasonable common mode isolation, it offered virtually no differential isolation. The foil trace from the PTT lead (that had no RF isolation at the jacks) ran right along side the audio trace. Bypassing to the case as a common ground, and splitting the power supply leads into two isolated chokes, totally cured the VOMAX. 73 Tom ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by W8JI
Tom W8JI escribió:
> <<<<I am trying to use a cheap computer microphone in my K3, front 8 pin > connector. I have some doubts that I would like to solve before making a > mistake: > > 1- Can I use pin 1 directly atached to the electret capsule and set bias > in config:MIC SEL? Or should I use also some kind of resistor/condenser > arrangement to the 8V DC pin6? > 2- For GND: shoul I use pin 7, pin 8 or both pins?>>>> > > > I just went through that. My Sennheiser headset now works fine using > internal settings for bias. > > Pin 7 and 8 are the same connection point. I do not believe it is best > that they are the same, in my unprofessional opinion one should be a > shield ground and one an audio ground, but they are the same. Oh yes, thanks for your help. I have mine working now. I have to get optimal gain and compression adjustments, but the microphone works great at first glance. > > I had to modify my audio input grounding to cure RFI. My headset has a > long cord, and when I would stretch the cord I would get bad RFI with my > yagi stacks pointed back at my house. Elecraft has a mod for this, but I > changed more. I soldered the wire around the mic connector shell to the > connector shell, and I grounded the circuit board pin 7 and 8 via a > copper foil that grounds under the cabinet screw in that corner. > > Now I absolutely no RFI into the audio no matter what I do, and with the > very long cord all stretched out like an antenna! The Elecraft mod was > an improvement, but the copper foil was a total cure for me. Thank for the information Tom. If I get some RF problems I will do that. Thank you. 73, EA4NZ, (ex EA1ABZ) > > 73 Tom > > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Jim Brown-10
Thanks you very much Tom and Jim for the detailed responses. I have to
test my microphone for RFI. Jim, very interesting technical web page. I have explained my easy to make microphone in my web page. Sorry, it is only in spanish but the pictures speak for themselves. http://ea1abz.ure.es/microk3/microk3.html See you on the air (mainly in CW, my favorite mode, hi) Ramiro. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Very interesting, Ramiro, I might give that a go.
Good to see that the ABS plastic box is clearly marked "MADE IN ENGLAND". Unfortunately we don't see that as much as we used to ;-( 73 de David G4DMP In a recent message, Ramiro Aceves <[hidden email]> wrote ... > >Thanks you very much Tom and Jim for the detailed responses. I have to >test my microphone for RFI. Jim, very interesting technical web page. > >I have explained my easy to make microphone in my web page. Sorry, it is >only in spanish but the pictures speak for themselves. > >http://ea1abz.ure.es/microk3/microk3.html > >See you on the air (mainly in CW, my favorite mode, hi) > >Ramiro. David G4DMP Leeds, England, UK ------ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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David Pratt escribió:
> Very interesting, Ramiro, I might give that a go. > Good to see that the ABS plastic box is clearly marked "MADE IN > ENGLAND". Unfortunately we don't see that as much as we used to ;-( Yes! I also was surprised by the "made in England". That is a rare thing nowadays. Now everything is "made in china" (the computer microphone is made in china of course) or "made in Taiwan". Decades without seeing a "made in Spain" frase, hi,hi... Good college days... I am 39 now. Plastic box was expensive, around 5 euros. The same price as de microphone. I think there are cheaper computer microphones out there, but I liked the mic arm very much. PTT placement in the box is not optimal, I should have placed it on the top of the box, but there was nos room for that. -Computer microphone: 5 eur -Box: 5 eur -Mic connector: 4.5 eur -Cable: 1 eur -PTT switch: 1.2 eur - Green switch: 1 eur - RED switch: 0.85 eur -Yellow switch: 0.75 eu Total: 19.3 eur See you on the air. Ramiro, EA4NZ, ex EA1ABZ > 73 de David G4DMP > > In a recent message, Ramiro Aceves <[hidden email]> wrote ... >> >> Thanks you very much Tom and Jim for the detailed responses. I have to >> test my microphone for RFI. Jim, very interesting technical web page. >> >> I have explained my easy to make microphone in my web page. Sorry, it is >> only in spanish but the pictures speak for themselves. >> >> http://ea1abz.ure.es/microk3/microk3.html >> >> See you on the air (mainly in CW, my favorite mode, hi) >> >> Ramiro. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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