On 24 Feb 2006 18:29:20 -0800, "Michel Rouzic" <Michel0528@yahoo.fr> wrote:> >Jim Adamthwaite wrote: >> The noise waveform you describe (1.05uS pulse) sounds like digital >> interference, which would probably be there regardless of choice of >> transducer. > >I mesured on a sample of ten to be about 1.05 second long, but I >noticed on other parts of a recording that it can be shorter than that. > >> The last time I tried a (el-cheapo) speaker as a mike it was good for >> about 20 millivolts p-p. Your sound card ADC input probably wants >> about 2 volts peak to peak. The 100:1 voltage gain required (40 dB) >> which you are presumably doing in software will bring up the level of >> the noise by that amount. >> >> Jerry Avins' comment about a transformer is the simplest way to fix >> this. Get a speaker transformer of reasonable quality (minimum size of >> 1 cubic inch - you'd be surprised at how many things are better when >> they are heavier). >> >> The primary winding needs to be rated as having a primary impedance of 5 >> Kohms or greater, and the secondary at 8 ohms or less. Now connect the >> speaker (mike) to the 8ohm secondary. Connect the 5K winding to the >> ADC input & signal ground. > >ok thanks alot for the tip. i got alot of transformers hangin around so >i'll test so of them. > >> The transformer is now running "back to front" and giving you a step-up >> voltage multiplication of 25 to 1. This is about 28 dB gain. which >> should allow you to wind down your software gain by that amount. > >Just wondering, how do you calculate the voltage multiplication out of >the impedance of each part? Anyways I guess a 230 to 12 volt (or less) >transformer will do it, right?The impedance ratio is the square of the turns ratio. The turns ratio is the same as the voltage ratio. You probably should be using a tiny audio transformer, rather than a mains transformer. Radio Shack (or their equivalent in your part of the world) should have these in stock. Look at part 237-1146-ND from digikey: http://dkc3.digikey.com/PDF/T061/1619.pdf You could shop around and find an equivalent transformer for one hundredth the price. Regards, Allan
Improving the SNR of a mic
Started by ●February 23, 2006
Reply by ●February 24, 20062006-02-24
Reply by ●February 25, 20062006-02-25
Michel Rouzic wrote: ...> Just wondering, how do you calculate the voltage multiplication out of > the impedance of each part? Anyways I guess a 230 to 12 volt (or less) > transformer will do it, right?The voltage ratio is equal to the turns ratio. The impedance ratio is the square of that. You want an audio transformer for best results. A power transformer will be lossier at high frequencies. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●February 25, 20062006-02-25
Michel Rouzic wrote:> > Just wondering, how do you calculate the voltage multiplication out of > the impedance of each part?The voltage multiplication ratio IS the turns ratio. This is often not on the label, but can be deduced. As a first approximation, the load impedance which you connect to the output of the transformer determines how much load-side current which will flow for a given output signal. (Ohm's law: I=E/R). In our step up example, The input (mike) voltage will be 1/25th of the output voltage, and the input current drawn from the mike MUST be 25 times higher than the output load current (for power in & out to be the same). The transformer input will therefore look (from the mike's point of view) like a load with an impedance of 1/625th ( 1/(25*25) ) of whatever load you connect to the output. So the impedance ratio is the square of the turns ratio. If you know the rated i/p & o/p Z's, the turns ratio (N) is: N = sqrt( Zs / Zp) If you vary the load you connect to the output, the input impedance will vary proportionally. Transformers do not have a fixed impedance, the manufacturer is just specifying the design-centre range for optimal performance.> Anyways I guess a 230 to 12 volt (or less) transformer will do it,right? Yes, a mains transformer will do fine for voice quality. Treble response will probably be dropping before you reach 20KHz due to high inter-turn secondary winding self-capacitance. As the mike signal power is so low you need not concern yourself about core non-linearity issues. A transformer with multi-tapped (e.g. 230:6/12/15V) will allow easy experimentation. BTW, does your sound card have a microphone (high gain) input? Jim A.
Reply by ●February 25, 20062006-02-25
why are you trying to use a speaker as a mic a speaker makes a terrible mic get a cheap radio shack condensor mic with a built in prepamp...it will work 1000% better than any speaker most comouter "mic" inputs are designed to supply a small DC voltage for these condensor mics so you will be all set to go... (P.S. I'm not talking about +48 so called phantom power used in professional audio gear) Mark
Reply by ●February 25, 20062006-02-25
Mark wrote:> why are you trying to use a speaker as a mic > > a speaker makes a terrible mic > > get a cheap radio shack condensor mic with a built in prepamp...it will > work 1000% better than any speaker > > most comouter "mic" inputs are designed to supply a small DC voltage > for these condensor mics so you will be all set to go... > > (P.S. I'm not talking about +48 so called phantom power used in > professional audio gear)Maybe it makes a terrible mic, but that's all I had under the hand, and the advantage is since it came by two I could use one as a speaker and the other as a mic in order to calibrate the two. No radio shack around here, and I'm not going to town very often anyways, so I really better count on what I already have.
Reply by ●February 25, 20062006-02-25
On Sat, 25 Feb 2006 14:44:13 +1100, Allan Herriman <allanherriman@hotmail.com> wrote: [snip]>You probably should be using a tiny audio transformer, rather than a >mains transformer. >Radio Shack (or their equivalent in your part of the world) should >have these in stock. > >Look at part 237-1146-ND from digikey: >http://dkc3.digikey.com/PDF/T061/1619.pdf >You could shop around and find an equivalent transformer for one >hundredth the price.... or even cheaper if you pull one out of a 1970s style transistor radio. Regards, Allan
Reply by ●February 27, 20062006-02-27
Jim Adamthwaite wrote:> Michel Rouzic wrote: > > > > Just wondering, how do you calculate the voltage multiplication out of > > the impedance of each part? > > The voltage multiplication ratio IS the turns ratio. This is often not > on the label, but can be deduced. > > As a first approximation, the load impedance which you connect to the > output of the transformer determines how much load-side current which > will flow for a given output signal. (Ohm's law: I=E/R). > > In our step up example, The input (mike) voltage will be 1/25th of the > output voltage, and the input current drawn from the mike MUST be 25 > times higher than the output load current (for power in & out to be the > same). > > The transformer input will therefore look (from the mike's point of > view) like a load with an impedance of 1/625th ( 1/(25*25) ) of > whatever load you connect to the output. > > So the impedance ratio is the square of the turns ratio. If you know > the rated i/p & o/p Z's, the turns ratio (N) is: N = sqrt( Zs / Zp) > > If you vary the load you connect to the output, the input impedance will > vary proportionally. > > Transformers do not have a fixed impedance, the manufacturer is just > specifying the design-centre range for optimal performance. > > > > Anyways I guess a 230 to 12 volt (or less) transformer will do it, > right? > > Yes, a mains transformer will do fine for voice quality. Treble > response will probably be dropping before you reach 20KHz due to high > inter-turn secondary winding self-capacitance. > > As the mike signal power is so low you need not concern yourself about > core non-linearity issues. > > A transformer with multi-tapped (e.g. 230:6/12/15V) will allow easy > experimentation. > > BTW, does your sound card have a microphone (high gain) input?yes it does and that's what i'm using, but because I need to amplify it to the maximum I get lots of noise. However i just realized that my soldering iron is dead (doesn't warm up and testing the two power connectors's resistance show no conductivity) and that i have the choice between either investing in a new one as I use it like once every three years, otherwise buy a $10 microphone. Any suggestiongs for a $10 microphone?
Reply by ●February 27, 20062006-02-27
Michel Rouzic wrote:> Any suggestiongs for a $10 microphone?Radio Shack sells a small electret capsule for about a third of that which is of surprisingly good quality. It requires a resistor, a capacitor a battery and a cable with 1/8" plug on it. The simple circuit diagram used to be printed on the package that it comes in. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein
Reply by ●February 27, 20062006-02-27
Michel Rouzic wrote:> Jim Adamthwaite wrote: > >>Michel Rouzic wrote: >> >>>Just wondering, how do you calculate the voltage multiplication out of >>>the impedance of each part? >> >>The voltage multiplication ratio IS the turns ratio. This is often not >>on the label, but can be deduced. >> >>As a first approximation, the load impedance which you connect to the >>output of the transformer determines how much load-side current which >>will flow for a given output signal. (Ohm's law: I=E/R). >> >>In our step up example, The input (mike) voltage will be 1/25th of the >>output voltage, and the input current drawn from the mike MUST be 25 >>times higher than the output load current (for power in & out to be the >>same). >> >>The transformer input will therefore look (from the mike's point of >>view) like a load with an impedance of 1/625th ( 1/(25*25) ) of >>whatever load you connect to the output. >> >>So the impedance ratio is the square of the turns ratio. If you know >>the rated i/p & o/p Z's, the turns ratio (N) is: N = sqrt( Zs / Zp) >> >>If you vary the load you connect to the output, the input impedance will >>vary proportionally. >> >>Transformers do not have a fixed impedance, the manufacturer is just >>specifying the design-centre range for optimal performance. >> >> >> >>>Anyways I guess a 230 to 12 volt (or less) transformer will do it, >> >>right? >> >>Yes, a mains transformer will do fine for voice quality. Treble >>response will probably be dropping before you reach 20KHz due to high >>inter-turn secondary winding self-capacitance. >> >>As the mike signal power is so low you need not concern yourself about >>core non-linearity issues. >> >>A transformer with multi-tapped (e.g. 230:6/12/15V) will allow easy >>experimentation. >> >>BTW, does your sound card have a microphone (high gain) input? > > > yes it does and that's what i'm using, but because I need to amplify it > to the maximum I get lots of noise. > > However i just realized that my soldering iron is dead (doesn't warm up > and testing the two power connectors's resistance show no conductivity) > and that i have the choice between either investing in a new one as I > use it like once every three years, otherwise buy a $10 microphone. > > Any suggestiongs for a $10 microphone?http://jameco.com/webapp/wcs/stores/servlet/CatalogSearchResultView?langId=-1&storeId=10001&catalogId=10001&searchType=k&searchValue=microphone&categoryId=504510 -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●February 27, 20062006-02-27
Michel Rouzic wrote:> Jim Adamthwaite wrote: > >>Michel Rouzic wrote: >> >>>Just wondering, how do you calculate the voltage multiplication out of >>>the impedance of each part? >> >>The voltage multiplication ratio IS the turns ratio. This is often not >>on the label, but can be deduced. >> >>As a first approximation, the load impedance which you connect to the >>output of the transformer determines how much load-side current which >>will flow for a given output signal. (Ohm's law: I=E/R). >> >>In our step up example, The input (mike) voltage will be 1/25th of the >>output voltage, and the input current drawn from the mike MUST be 25 >>times higher than the output load current (for power in & out to be the >>same). >> >>The transformer input will therefore look (from the mike's point of >>view) like a load with an impedance of 1/625th ( 1/(25*25) ) of >>whatever load you connect to the output. >> >>So the impedance ratio is the square of the turns ratio. If you know >>the rated i/p & o/p Z's, the turns ratio (N) is: N = sqrt( Zs / Zp) >> >>If you vary the load you connect to the output, the input impedance will >>vary proportionally. >> >>Transformers do not have a fixed impedance, the manufacturer is just >>specifying the design-centre range for optimal performance. >> >> >> >>>Anyways I guess a 230 to 12 volt (or less) transformer will do it, >> >>right? >> >>Yes, a mains transformer will do fine for voice quality. Treble >>response will probably be dropping before you reach 20KHz due to high >>inter-turn secondary winding self-capacitance. >> >>As the mike signal power is so low you need not concern yourself about >>core non-linearity issues. >> >>A transformer with multi-tapped (e.g. 230:6/12/15V) will allow easy >>experimentation. >> >>BTW, does your sound card have a microphone (high gain) input? > > > yes it does and that's what i'm using, but because I need to amplify it > to the maximum I get lots of noise. > > However i just realized that my soldering iron is dead (doesn't warm up > and testing the two power connectors's resistance show no conductivity) > and that i have the choice between either investing in a new one as I > use it like once every three years, otherwise buy a $10 microphone. > > Any suggestiongs for a $10 microphone?http://jameco.com/webapp/wcs/stores/servlet/CatalogSearchResultView?langId=-1&storeId=10001&catalogId=10001&searchType=k&searchValue=microphone&categoryId=504510 http://jameco.com/webapp/wcs/stores/servlet/CatalogSearchResultView?langId=-1&storeId=10001&catalogId=10001&searchType=k&searchValue=microphone&categoryId=504520 -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
