Comments on electret mic amp
Comments on electret mic amp
(OP)
Been rummaging through my junk drawer as of late and decided to play with electret mics for an upcoming project. I'd appreciate any "10,000-foot level" feedback you guys might have on the circuit, be it the actual connections or just the values. This is by no means a high-quality/low-noise piece, just enough to get a reasonable reproduction of the sound sent to a filter bank.
Thanks!
FYI: The mic I'm using has an impedance of 2.2kohm with a standard operating voltage of 2.5V (10V max). I believe I set up the voltage divider correctly (too many sleepless nights of designing may have let a bad number slip by). The 100k is in there for negative feedback, but the emitter resistor should do some of the same (think I should kill off the 100k?). The 1uF caps should be large enough to let the bass through (but again, I could have been sleeping at the wheel).
Thanks!
FYI: The mic I'm using has an impedance of 2.2kohm with a standard operating voltage of 2.5V (10V max). I believe I set up the voltage divider correctly (too many sleepless nights of designing may have let a bad number slip by). The 100k is in there for negative feedback, but the emitter resistor should do some of the same (think I should kill off the 100k?). The 1uF caps should be large enough to let the bass through (but again, I could have been sleeping at the wheel).
CODE
+12V o---|----------------------|
| |
| 1k
| |
| |-----------|----1uF------o
12k | | Output
| 100k ____| o
| | |/ |
o---|----1uF---|-----| 2N2222 -----
In |\____ ---
o | -
| 82ohm
----- |
--- -----
- ---
-
| |
| 1k
| |
| |-----------|----1uF------o
12k | | Output
| 100k ____| o
| | |/ |
o---|----1uF---|-----| 2N2222 -----
In |\____ ---
o | -
| 82ohm
----- |
--- -----
- ---
-





RE: Comments on electret mic amp
RE: Comments on electret mic amp
1µF at the input is ok because the input impedance of the transistor stage is of the order of kilohms. At the output, however, the impedance may be lower (tens of ohms?) and the coupling time constant would then be too small.
RE: Comments on electret mic amp
I haven't analyzed them, but I've come across several circuits with similar characteristics... I wonder how they operate in the real world:
http://www.brainz90.karoo.net/mic-amp.htm
This circuit looks nice, not overly complicated, but there are inconsistencies (for example, the supply is shown as 6-30V, but most electret mics won't take more than about 10V):
http:/
I'm still liking my original circuit for low-cost/complexity reasons, though. You just can't beat a sub-nickel NPN, a few sub-penny resistors, and a couple of sub-nickel caps for price... that 100uF cap practically doubles the price of the whole circuit!
If you think any other values are out of range, though, please let me know. My next step is to put together some Sallen-Key filters (LP/HP/BP) after the AGC... I hate messing with the values since I can't separate Q and gain (especially on the BP).
RE: Comments on electret mic amp
RE: Comments on electret mic amp
of what you're driving is high enough, say above 4kohm