I swapped a bad two-wire electret for a medium one in a Bluetooth microphone I bought, and I have found a three-wire Tascam electret which has yellow, red, and black wires. Can I connect it to a two-wire amplifier?
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3\$\begingroup\$ If you don't have some data on those devices what the 2 and 3 wires are then you can't know if they are compatible and how they should be connected together. \$\endgroup\$– JustmeCommented Oct 4, 2022 at 4:27
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3 Answers
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Two wire electret microphones have an FET in a common source arrangement, the source is grounded and the drain is connected to positive through an external resistor. The output is taken from the drain.
simulate this circuit – Schematic created using CircuitLab
A three wire electret mic has an FET wired as a common drain or source follower. The positive voltage goes to the drain, and the source is connected to ground through an external resistor. Audio is taken from the source.
You could try rewiring the three wire mic to work like a two wire by connecting the yellow and black.
It might just work. If it doesn't it might not be biased right, you could try different values for the bias resistor and/or adding a parallel resistor and capacitor between the yellow and black.
These circuits are the common types used in electret mics, there may be other configurations out there so your miles may vary.
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\$\begingroup\$ Thanks! awesome advice, the preamp is producing so much noise with all the other electrets except the one I bought it with, i'll have to post a new question about it. \$\endgroup\$ Commented Oct 4, 2022 at 10:36
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You can but no promises; if you have enough gain in your amplifier to make it work. Try this use the yellow as the signal side and the black as ground. You could also try tying the red and black together. The Red is +, the black is -, and yellow is the audio referenced to -. The other option is to connect it as it should be. Connect a battery (1 to 9V) red being positive, black as -. Then connect the black as ground and yellow as the hot signal. A simple battery will probably last 6 months or more. The battery powers the internal FET amplifier.
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\$\begingroup\$ "If you have enough gain"? The two-wire circuit produces a lot more gain (10dB or more) than the three-wire circuit, at the cost of THD, impedance, maximum SPL. Gain is the one thing you'll have plenty of. \$\endgroup\$ Commented Oct 5, 2022 at 15:25
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A 3-wire electret can be used as 2-wire by tying together the yellow and black wires. The fallacy here is that the 2-wire circuit has higher gain, higher output impedance, and might impact the trebles.
The most likely of those problems in practice is that a 3-wire capsule used in a 2-wire circuit might start clipping at lower volumes than desirable because of being selected for high gain. "bluetooth microphone" sounds like intended for normal speech: that will likely work well enough.
