jmccanna said:Hi,
Old post but new question from a newbie. Could the last schematic just above this from Samuel Groner titled "simple 5V mic pre.pdf" be powered by the usb port with the line out going to the line in on a netbook?
And, would it work with an electret capsule like the Primo EM-172? The Spec sheet for the Primo I think says it operates at 2.4k ohms +/- 30% at 1kHz. (I unfortunately do not know what that means).
James
Yes and yes.
To adapt to electret replace R9 with 3.9 k to 5 V and reduce C5 to fit with the new source resistance, say around 150 pF for the same HF rolloff.
Current in the input transistor may need to be scaled down as well for good noise performance... Maybe about 0.24 mA assuming hfe of around 500. This is about an order of magnitude less than the original design, so just scale R1, R5 and R6 up ten times.
But...
Do you really want to apply 40 to 60 dB of gain? This would make the output clip at about 86 to 67 dB SPL. At what level does the input of the computer clip? What is the level of the signals you wish to record?
Overall there seems to be much simpler routes to go with this, since it will be quite 'ghetto' regardless.. A simple opamp stage could probably perform well here, and be more flexible wrt. gain range..