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Audio and Video Talk
The Vintage Audio Section
Kenyon mic pre transformer
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<blockquote data-quote="handsome" data-source="post: 976746" data-attributes="member: 772"><p>Feed a small ~10mV 1kHz signal into one end and measure what come out the other end! This will give your the voltage ratio of the device and determine which windings are primary and which are secondary. Once you know your voltage ratio you can design your preamp.</p><p></p><p>Dynamic microphones are - generally - 200R impedance. So as rough rule of thumb you can use a load resistance of: 200 x (voltage ratio squared) If you have an oscilloscope you can then feed a square wave (~10mV) into the device via a suitable series resistor (200R minus your generator's output impedance) and use your predetermined load resistance then determine what Zoebel network (if any) will be necessary to give you the least amount of ringing. If you don't have a scope but can measure frequency response beyond 20kHz you can do the same to eliminate the resonant peak (if any).</p><p></p><p>Don't try and measure with a multimeter - this will put DC through the device and could magnetise it. Only use an AC source to do measurements. If you have a multimeter that is not fancy measure the device with a 100Hz signal as most multimeters even the True RMS ones, cannot accurately read AC above ~500Hz - they are all optimised for reading mains frequencies.</p></blockquote><p></p>
[QUOTE="handsome, post: 976746, member: 772"] Feed a small ~10mV 1kHz signal into one end and measure what come out the other end! This will give your the voltage ratio of the device and determine which windings are primary and which are secondary. Once you know your voltage ratio you can design your preamp. Dynamic microphones are - generally - 200R impedance. So as rough rule of thumb you can use a load resistance of: 200 x (voltage ratio squared) If you have an oscilloscope you can then feed a square wave (~10mV) into the device via a suitable series resistor (200R minus your generator's output impedance) and use your predetermined load resistance then determine what Zoebel network (if any) will be necessary to give you the least amount of ringing. If you don't have a scope but can measure frequency response beyond 20kHz you can do the same to eliminate the resonant peak (if any). Don't try and measure with a multimeter - this will put DC through the device and could magnetise it. Only use an AC source to do measurements. If you have a multimeter that is not fancy measure the device with a 100Hz signal as most multimeters even the True RMS ones, cannot accurately read AC above ~500Hz - they are all optimised for reading mains frequencies. [/QUOTE]
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Audio and Video Talk
The Vintage Audio Section
Kenyon mic pre transformer
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