John Curl's Blowtorch preamplifier part II

[john curl]

Richard makes sense. It should be realized by everyone that mike design has been going on for a very long time, people have seriously tried to overcome limitations in virtually every type of mike concept, and that there are ALWAYS TRADEOFFS.

[Wavebourn]

It is by definition: design means optimization.

[scott wurcer]

Originally Posted by john curl

people have seriously tried to overcome limitations in virtually every type of mike concept, and that there are ALWAYS TRADEOFFS.

It is good to be reminded that the thermal noise of the air pressure on the diaphragm limits the noise at mid-high frequencies and the RF techniques are lower noise mainly at the low end because they don't need the G-Ohm bias resistor. There is a trade off in terms of reliabiliy and JFET leakage that makes a commercial designer think twice about simply dropping in a 50G Ohm resistor.

[Wavebourn]

If we speak about condenser microphone, there is an optimal diaphragm size, as a compromise between noise level and upper frequency response. Neuman microphones were successful because they found this optimum for frequency response that was standard then. No need for 50G resistors, and even 0.5G resistors are shunted well by about 100 pF of the capsule capacitance.

[Esperado]

Originally Posted by scott wurcer

There is a trade off in terms of reliabiliy and JFET leakage that makes a commercial designer think twice about simply dropping in a 50G Ohm resistor.

Yes, and best IGBTs have a lower noise factor than FETs.

[bcarso]

Originally Posted by Esperado

Yes, and best IGBTs have a lower noise factor than FETs.

Please give us an example!

[Wavebourn]

Originally Posted by bcarso

Please give us an example!

Probably he means less interference from light dimmers with IGBT than from light dimmers with FETS?

[scott wurcer]

Originally Posted by Wavebourn

If we speak about condenser microphone, there is an optimal diaphragm size, as a compromise between noise level and upper frequency response. Neuman microphones were successful because they found this optimum for frequency response that was standard then. No need for 50G resistors, and even 0.5G resistors are shunted well by about 100 pF of the capsule capacitance.

Still a few dB of room for improvment at those numbers, but yes at 1" it works. They still had to work hard to get the frequency response.

[Kindhornman]

Santa,
I want a 1/4" B&K microphone for Xmas for testing your speakers for the North Pole. And you can include the power supply that goes with it. I don't care how old it is as long as it works. Would help me with my beryllium dome tweeter development, my Earthworks mike won't go that high.

ps. I have tried to be a good boy this year and keep out of trouble. Thanks for bringing down the price of neodymium magnets this year.

[dimitri]

1/4" B&K microphone, preamp and battery powered power supply will be around $1K on fleabay
or you can replace preamp and battery powered power supply with 4048 ACO Pacific phantom powered preamp(body)
I can lend you 1/4" B&K microphone.