ryeeson

I already test the cricuit but its wont working. The circuit can't detect any signal :( what wrong here?? i thinks there wasnt have enough gain. i used DC power supply(singgle supply + and ground). i revert back to the original circuit ant its working. but the second stage of the peramp seem dont have any benefit. can u help me? may be by showing your draw that you used before??

How do i power up my MC33171? i post the picture here. i just want to make sure it. do i need a supply power for each of my MC33171?

Thanks... ;D ;D ;D I just need to calibrate my circuit using the 2 volume control. ;D ;D i try to calibrate it first by myself before go to a company. may be i can use the computer microphone since there is a built in software for displying the noise level?? I only can calibrate after i finished the circuit.. damm have to wait until 30 dec. btw, i dont need very accurate Sound Level Meter. Merry Christmas pal..

Thanks again. Another question is, can we change the Mic's sensitivity? when come into calibrate topic, i know nothing.. :( do you mean i need to go to sound system company and ask them to calibrate my circuit? ???

I dont have a sound level meter. I assume that the LM3915 will be able to acting as a Sound Level Meter. am i correct here??? ???

Hai Audioguru, I might try your peramp design if my current peramp could not met the required level. I went to my local farnell today only to find out that they out of stock for the MC33171N and it quite expensive. My order will only avilable on friday next week. Until that time, i cannot show you the result. i am Newbie in electronic project (this is my 1st project). I plan to connect the LM3915 to a PIC16F84 Microcontroller. Let say if i set 50dB is the limit of allowed noise level inside the library. the pin (at 50+ dB) on LM3915 is connected to one of the interrupt pin on PIC16F84. When the noise level exceed the allowed level, the LM3915 will tigger the interrupt and the PIC now will run a program to blinking an warning LED to the user library 8). this is a part of my project ;D

i choose MC33171N. I saw another model, MC33171P. Is the different will take effect? Thank You.

They dont have the MC33171. i'm going uptown. If i dont used a negative supply, i must place resistor in series with the (+ pin) M3C33171 to ground? or i just buy the MC33172 instead? What value a the baypass capasitor do you recomand for the LM3915? btw, i will use the 1N4148 for the half wave detector. Is there is any problem with it?

well, i update you latter after testing it in LAB. Do you recomand the TL071 as a opamp for the preamp?

Here is my ugly circuit after consedering your comment. Sorry again because i use hand drawing(i dont have a software) -- poor guy here :'( The peramp stage is taken from some forum. they recomand me that peramp. Any comment?

Sorry For the Late Reply. :P(i dont have internet connection yet in my house :P) I want to measure a noise in the library. So if the library user causing a noise, the noise level meter will vary accroding to the noise. Basiclly, i want to build an noise indicator. i dont use either the precision half-wave or full wave average or peak detector circuit. --"Without one the LEDs will momentarily blink real-time and be very dim and a blur"?? ??? so do u have any suggestion which one i need to use? "Did you use figure 5 or figure 6 to cascade the LM3915's? Is full-range set at 10V?" So this mean, it is not suitable for a weak signal??? ??? i used figure 6. I'm operating the LM3915 in Bar Mode. Where should i connect the bypass capasitor??? :-\ i used Condenser mic, 2-wire. i' not sure if it has a built-in FET. i'll attach schematic as soon as i caome back online. acctuly i used power amp because i was thought the signal is weak and need to be amplify.

i want to build an noise Level meter using LM3915 0dB-60dB. i already design my noise detector and also the peramp+20w power amplifier which is work well after testing using the osciloscop. The output from the 20w PA is connected directly to a cascaded LM3915(Figure 7 in LM3915's data sheet on application hint topic). the probelm is, some of the LED wont light up and only detect noise if the noise is closed enough(9-13 cm) to the mic. when testing with the osciloscope, the output of the 20W power amp can vary(very sensetive) according to the noise while the noise's source is within 0.7 meter from the mic. What wrong with my LM3915 driver?? low power input signal???? http://www.ee.washington.edu/stores/DataSheets/linear/lm3915.pdf