Using the element below I will make a microphone to drive a preamp, then an amp. The mic will consist of the element, a 10k log pot, and a 1/4" audio jack housed in a plastic spice container about 4"long, 1 3/4" wide.
Questions:
1. Should these parts be wired with coax, and if so what type of coax?
2. Should the cable from the mic to the preamp be coax, and if so what type?
3. Should the cable from the preamp to the amp be coax, and what type?
4. Is it necessary to put shielding on the inside of the container, such as tin foil?
This is the mic element:
Ceramic/Crystal NOS Microphone Element/Capsule Harmonica, Harp, Mic, Hi Z, Blues. These Elements use the same old school technology as the original crystal microphones from the 50's and are sourced from Japan. They are High Impedance so no Audio Transformer is needed.
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Technical data Sensitivity -60 dB
Frequency range 300 - 10 000 Hz
Dimensions (Ø x H) 31 mm x 9 mm
Impedance 200 kΩ
Questions:
1. Should these parts be wired with coax, and if so what type of coax?
2. Should the cable from the mic to the preamp be coax, and if so what type?
3. Should the cable from the preamp to the amp be coax, and what type?
4. Is it necessary to put shielding on the inside of the container, such as tin foil?
This is the mic element:
Ceramic/Crystal NOS Microphone Element/Capsule Harmonica, Harp, Mic, Hi Z, Blues. These Elements use the same old school technology as the original crystal microphones from the 50's and are sourced from Japan. They are High Impedance so no Audio Transformer is needed.
.
Technical data Sensitivity -60 dB
Frequency range 300 - 10 000 Hz
Dimensions (Ø x H) 31 mm x 9 mm
Impedance 200 kΩ
At least twisted pair.
Screened twisted pair is better at attenuating interference.
Screened star quad is better again but has higher capacitance and the high source impedance will almost certainly not suit this.
Is the impedance really 200k?
Could that 200k be the recommended load impedance?
Locate the pre as close to the mic as possible.
Use a screened box for the pre, you are working with small signals.
What does that -60dB for sensitivity mean?
What is the voltage output for what level of SPL input?
Screened twisted pair is better at attenuating interference.
Screened star quad is better again but has higher capacitance and the high source impedance will almost certainly not suit this.
Is the impedance really 200k?
Could that 200k be the recommended load impedance?
Locate the pre as close to the mic as possible.
Use a screened box for the pre, you are working with small signals.
What does that -60dB for sensitivity mean?
What is the voltage output for what level of SPL input?
Seem to be good questions, but this is all the information in the specs for the mic. What does the 200k ohm impedance tell us about selecting a preamp?
The mike impedance itself will be a capacitor. 200k will be the recommended load impedance. A 10k pot will remove all the bass. You need a 250k pot if you really want to put a volume control right at the mike, but this will be noisy.
200k output impedance means you'd like to drive one tiny JFET gate or tube grid with it. The input impedance should be over 10 Megohms. Easiest way would be a low noise JFET input opamp like OPA134. I saw your first related post. There's no way to drive a chip amp with a crystal mic directly.
OK, so where to go from here to use this mike as a harmonica microphone? I imagine I can forego the potentiometer with mic if the preamp has a pot control...
What off the shelf or ready to build kit - preamp that will work with this? I assume I can then use any suitable power amp.
Should the preamp be in the mic housing, or can it be 8 feet away, at the end of the mic coax cable?
I can build a preamp circuit from scratch if necessary, if I have a schematic.
What off the shelf or ready to build kit - preamp that will work with this? I assume I can then use any suitable power amp.
Should the preamp be in the mic housing, or can it be 8 feet away, at the end of the mic coax cable?
I can build a preamp circuit from scratch if necessary, if I have a schematic.
A preamp in the mike housing will give the advantage that the cable can then be about as long as you like. Disadvantage is providing power for it.
A JFET source follower might be sufficient.
A JFET source follower might be sufficient.
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