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Looking for suggested dynamic microphone power level

HANKMARS

Jul 28, 2019
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I use a dollar twenty five cent headset microphone for recording purposes on my computer. I have made the assumption that an auxiliary source of current is needed to travel thru the mic to supply the varying converted audio waves to analog signal driving the amplifier inputs or maybe the power out amp pre-amp. Anyway, if you can toss me a current value for a starting point and how it is coupled to mic and amplifier circuits I'll try it out. I suppose I can interrupt the existing mic to computer plug and panel jack but...... My amplifier max gain is 200. Amp device ratings suggest Wout/max = 3 watts. Nominal amp Vs = +12 VDC ( Vs range is +8 to +15 VDC.) Nominal speaker Z = 8 ohms.
 

HANKMARS

Jul 28, 2019
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Myself, being mostly ignorant of anything microphonish, from lack of experience, referred to my Dollar Store headset microphone as a dynamic mic. Silly me. I did that based on the SWAG that since its output was negligible in an unpowered mode it was therefore "static" and required an active electrical current to produce transduced sound waves therefore making the relationship of amp to mic a dynamic circuit. Well, bite my.......tongue. Had it just backwards. The condenser/cap mic is the type of mic requiring pseudo power. Power which is used only to induce an electrical polar charge on one electrode of the capacitive audio transducer. About the only voltage values I have seen mentioned are 5 VDC and 48 VDC. My computer mic panel reads a DC voltage ~ 2.8. I am going to use 3.6 V. As the applied "phantom" power increases, so does Wo/mic. So far so good. I have not yet released any critical component smoke.
 

Audioguru

Sep 24, 2016
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An "electret mic" is a condenser mic with 48VDC permanently stored in some electret material. The condenser has an extremely high impedance so the mic has a Jfet as an impedance reducer and needs 500uA max (maybe actually 350uA to 400uA) to power the Jfet through its load resistor (maybe 4.7k) from 5VDC. Most electret mics have 2 wires (output/power and ground) But some have 3 wires (5V power without resistor, output and ground).
 

HANKMARS

Jul 28, 2019
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An "electret mic" is a condenser mic with 48VDC permanently stored in some electret material. The condenser has an extremely high impedance so the mic has a Jfet as an impedance reducer and needs 500uA max (maybe actually 350uA to 400uA) to power the Jfet through its load resistor (maybe 4.7k) from 5VDC. Most electret mics have 2 wires (output/power and ground) But some have 3 wires (5V power without resistor, output and ground).
Am I correct in my assumption that other earlier generation condenser mics of simpler construction are still manufactured these days? I'll try to attach a photo of the headset with which I am experimenting. This mic reads approx 800 ohms across its 1/8" plug contact areas. What I am seeing as a viable use for this mic and a stand alone audio amplifier the I use for my personal use of driving medium size speakers located outdoors, is, e.g. an auctioneer's PA unit, or a band instructor when addressingHEADSET DT 1.1.jpghis members on a football field, etc. The audio signal supplied to this amp generally is a tether to my phone or to the computer. I have found that these super cheap headset units have a quality level good enuf to be helpful in recording my musical practice for evaluation. I also am thinking that if proper record volume levels and proper mic placement are used, these mics would be alright for public performance. Not sure about that but I get a much richer sound using a mic to tranduce my 12 string sound than any "add-on" pick up that I have tried. So while I am working with mics with regard to music, I thot I would ponder using the cheapies for a PA unit which will take some investigation on my part.
 

HANKMARS

Jul 28, 2019
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Seriously, if I were to perform in public, I would likely spend the 10 - 30 dollar price of a cheapo condenser mic on Amazon. Mounting hardware and a semi-ruggid enclosure would be included so as I would not have to fabricate pieces.
 

Audioguru

Sep 24, 2016
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I assume that your headset mic is an electret type and your ohm-meter is causing its Jfet to conduct a little showing 800 ohms.
1) Its 2 wires need the correct polarity: positive on the signal wire and 0V on its shield wire.
2) Its output level is too low (about 10mV) to feed a power amplifier, a preamp in between is needed.
EDIT: The gain of your amplifier is 200 then it already has a preamp in it. But you need a filtered source of about 5VDC to feed the 4.7k mic's load resistor feeding power to the mic.
 
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HANKMARS

Jul 28, 2019
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I assume that your headset mic is an electret type and your ohm-meter is causing its Jfet to conduct a little showing 800 ohms.
1) Its 2 wires need the correct polarity: positive on the signal wire and 0V on its shield wire.
2) Its output level is too low (about 10mV) to feed a power amplifier, a preamp in between is needed.
EDIT: The gain of your amplifier is 200 then it already has a preamp in it. But you need a filtered source of about 5VDC to feed the 4.7k mic's load resistor feeding power to the mic.
The following attachment (or similar info) is what has been influencing my conclusions and train of thot. It was my intention to use a 3.6 VDC supply virtually where the cross-section diagram shows "battery." The 3.6 V can be produced by a secondary CV circuit using amp supply of 12 VDC or my newest amp Vs of 8 AA cell battery pack with nominal voltage of 9.6 VDC. I have bread-boarded the circuit using aux 3.6 V from a 3 cell battery holder. I do not know if my mic, not being damaged but this procedure, proves that it is not an electret type condenser mic but one of a different design.CONDENSER MIC OLDER CONSTRUC 1.1 .png
 

Audioguru

Sep 24, 2016
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The datasheet of an inexpensive electret mic shows how to power the Jfet inside it and shows that its output level drops if it is powered from a DC voltage that is too low.
I use this circuit that has a power supply filter:
 

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HANKMARS

Jul 28, 2019
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  • Shure SM58 Best Overall.
  • Shure SM7B Top Choice For Podcasts.
  • Rode PodMic.
  • Sennheiser e945 Best For Live Vocals.
  • Electro-Voice RE20.
  • Audio-Technica AT2005USB Budget Choice.
  • Shure SM57 Best For Instruments.
  • Beyerdynamic M160 Ribbon Microphone.
A couple articles implied that the Shure SM58 was an industry work horse. On Amazon the SM58 if referred to as a dynamic mic and I suppose it is, utilizing a movable coil in respect to a permanent magnet. For now and until a more polished sound is required for my music recordings of my practice runs, I will use my buck and a quarter headset microphone which my computer understands. If I should pursue fabricating any personal type PA units I will consider more refined units.
 

Audioguru

Sep 24, 2016
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You mentioned buying a cheapo electret mic on Amazon. It is modern and will probably work well.
Wkipedia says the 56 years old Shure SM58 dynamic mic is expensive so millions of poorly sounding fakes are sold (I think probably on ebay, AliExpress and Amazon).
 

Sunnysky

Jul 15, 2016
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The advantage of the 25-cent mic is the open back cancels distance sounds so it amplifies near sounds only with the mic near the corner of the lips. This is great to eliminate feedback with a loudspeaker due to the far field attenuation. The bad news is quality if this feature is all over the map so YMWV. The JFET Pull-Up R-value determines both the gain and DC midpoint of V+ due to the IDSS value of the FET being internal to the mic is another variable. Get a variety of different sources of electrets for comparison in quality. Use good shielded cable if the leads are long to the power amp.
 

HANKMARS

Jul 28, 2019
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The advantage of the 25-cent mic is the open back cancels distance sounds so it amplifies near sounds only with the mic near the corner of the lips. This is great to eliminate feedback with a loudspeaker due to the far field attenuation. The bad news is quality if this feature is all over the map so YMWV. The JFET Pull-Up R-value determines both the gain and DC midpoint of V+ due to the IDSS value of the FET being internal to the mic is another variable. Get a variety of different sources of electrets for comparison in quality. Use good shielded cable if the leads are long to the power amp.
The dollar mic I use does require that the sound source be somewhat near it. My current main use for a mic is to record acoustic guitar sounds. If I point the mic at the guitar and guitar is 2 to 5 feet from the mic, the recorded sound is surprisingly good. I am sure you are correct about a wide spectrum of quality levels. What is YMMV?
 

HANKMARS

Jul 28, 2019
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I assume that your headset mic is an electret type and your ohm-meter is causing its Jfet to conduct a little showing 800 ohms.
1) Its 2 wires need the correct polarity: positive on the signal wire and 0V on its shield wire.
2) Its output level is too low (about 10mV) to feed a power amplifier, a preamp in between is needed.
EDIT: The gain of your amplifier is 200 then it already has a preamp in it. But you need a filtered source of about 5VDC to feed the 4.7k mic's load resistor feeding power to the mic.
I'm sending a link to video (audio actually) made using my dollar tree mic. Bassline was recorded first. During its playback, lead was added. Duo was played back on Windows Media Player where equalizer and playback speed apps, among others, could be used. Then that playback was rerecorded to make final track. Interesting project. Recording device is Dell computer with voice recorder app. Electric guitar amp is hundred dollar Pyle 60 W amp. Guitar is 30 dollar thrift store buy.
 

Audioguru

Sep 24, 2016
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Your recording is missing high audio frequencies like an AM radio. Mayve the problem is caused by the very cheap mic or the "guitar speaker" or the bandwidth limited "voice" recorder app that produce no high audio frequencies.
 

HANKMARS

Jul 28, 2019
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Your recording is missing high audio frequencies like an AM radio. Mayve the problem is caused by the very cheap mic or the "guitar speaker" or the bandwidth limited "voice" recorder app that produce no high audio frequencies.
I may have wiped out those freqs with equalizer. For whatever reason, if I increase intensity of freq bars 1 kHz or 2 kHz they generally bring along a hiss or static. I'm guessing computer fan motor, frig, I am uncertain. I am intentionally trying to emphasize the bass sounds. Led Zepellin Bring it on Home has a rich baseline in the song introduction. Electric guitar is very new to me. It is a bit overwhelming the multitude of sounds available, so I do get skewed when calling pitches by ear. I appreciate your input.
 

Audioguru

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I do not like the severe distortion produced by an electric guitar and its distortion pedals. The speakers used are far from hifi that I like.
An acoustic guitar recording that sounds the same as a live player is what I like to hear.
 

HANKMARS

Jul 28, 2019
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I do not like the severe distortion produced by an electric guitar and its distortion pedals. The speakers used are far from hifi that I like.
An acoustic guitar recording that sounds the same as a live player is what I like to hear.
I share the same sentiment mostly. My desire to record and/or amplify the sound of my acoustic guitar is the foundation of my audio quest. I tried the type of add-on pickup that holds on to the sound hole. I tried a pickup that is held to the guitar with a spring clip. Both styles were far from satisfactory. Where the neck meets the body, there is an extension that turns 90 degrees from the neck and matches the width band but dies out just short of the sound box back panel. I discovered that the butt end of that perpendicular support does give a certain degree of richness to the recorded guitar sound. As far as mating the clip pickup body to that particular small, not flat, surface is not worth the effort. So a microphone was the next logical choice. Some of the pieces I enjoy playing would sound much more complete with even the simplest accompaniment. Microphones are less expensive than I had guessed. Still, my recordings are for personal use and the occasional copyright application. Hifi is not paramount, but neither is a dead flat ringless trail off acceptable. I'm retired living mostly on what I get back from the SS Admin. I try to be frugal where I can. When I spotted this headset at Dollar Tree I was willing to gamble that dollar. I was pleasantly surprised to hear the quality of sound which the headset mic delivered. I was looking at thrift shops for used mics and amps but pretty fruitless search. It seemed more cost effective to buy a low-end amplifier than for me to be reinventing the wheel. Progress is being made on this project and time restraints are pretty leisurely. If you are an acoustic music enthusiast, watch for works done by Tommy Emmanuel and an artist named Billy Strings.
 

HANKMARS

Jul 28, 2019
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Your recording is missing high audio frequencies like an AM radio. Mayve the problem is caused by the very cheap mic or the "guitar speaker" or the bandwidth limited "voice" recorder app that produce no high audio frequencies.
I have done a couple experiments using my acoustic guitar as the sound source. As normal I would record live guitar music with Voice Recorder. Then move recording to Windows Media Player. There I could use graphic equalizer to enhance or level out the intensity of multiple freq ranges. To make a new music file, I would rerecord music sample from WMP output, using Voice Recorder. Being intentionally looking for changes in sound quality, it was obvious that Voice Recorder had muddied up the higher freq ranges. Soooo, maybe I should pull some savings out of my mattress and bite the bullet and purchase some actual music recording components. An objective second pair of ears is what I needed to categorize my zero cost recording system. Thanks. The last time I really did any lengthy music recording, it was on a reel-to-reel unit that my brother bought in Southeast Asia, in the late sixties. I think it was Sony brand. The dollar tree headset mic may have very well added to the degradation of sound quality, also.
 

Audioguru

Sep 24, 2016
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Some cheap recorder systems are designed to record a voice. They cut frequencies above 3kHz like a 100 years old telephone did.
Then most of the talking was, "What? What did you say?" over and over.
 
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