I'd like to pass from a mic/filter/amp circuit with the LM386 and powered by a 9v battery in single supply to a 3.7v equivalent using the PAM8403. In hi-fi audio the phantom DC is 48v. Is there any downside in using a voltage as low as 3.7?
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\$\begingroup\$ It won't run. Like trying to run a 48V circuit with 3.7V. \$\endgroup\$– DKNguyenCommented Jan 9, 2021 at 20:29
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\$\begingroup\$ there's simply different microphones with different supply voltage requirements and different current limiting inside. 9V would most definitely destroy my desk electret. Other mics won't do with less. Can't plug a professional 48V one into 9V and expect it to work, either. \$\endgroup\$– Marcus MüllerCommented Jan 9, 2021 at 20:29
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1\$\begingroup\$ 48V isn't used for electret mics, and it would kill them. 3.7V will be fine. In hi-fi audio you won't find either LM386 or PAM8403 so the mic requirements aren't relevant. (You might need an opamp gain stage between mic and PAM8403 though.) \$\endgroup\$– user16324Commented Jan 9, 2021 at 21:26
1 Answer
The electret phantom power only drives the Idss of a JFET with a crystal ceramic mic. such that the gain and DC rise with the pullup resistor. So it is ~ 1mA. The expected max input of the PAM8403 on 5V at max gain of 24dB (~21) supply is +/-0.5V which you could get by shouting into it. So it is not the "Line Levels" expected from PAM8403 and needs a 10x gain AC coupled.
Pro Audio Phantom power is another beast with moving-coil and amplifier for high quality. But some run on 3V and 1mA like Sony.
Take these mics, which all use 48 volts. A Sennheiser MKH800 draws 3.0 mA, a Neumann U87 draws .8 mA, while a Shure KSM 32 draws 4.6 mA and all Earthworks models draw 10 mA.
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\$\begingroup\$ Thanks @Tony. I used TL072 or LM358 for op-amp stages with 9v batteries. I see that the LM321 works with 3.7v but I never used it. Would you have any suggestion for the low current op-amp? \$\endgroup\$– LooCommented Jan 10, 2021 at 0:15
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\$\begingroup\$ Any CMOS Op Amp with that Vdd rating \$\endgroup\$– D.A.S.Commented Jan 10, 2021 at 1:07