If you are using a single supply, have you remembered to arrange for a correct half-supply operating point for each amplifier?

how so? I'm a circuits noob.....

 

Hmmm, have you read the last few posts?

Let's back this up a bit - a few questions:

1. Are you using a single or dual supply?
2. Are you using a circuit designed for a single or dual supply?
3. Have you checked the DC voltage at each amplifier output? Are they nicely balanced somewhere between the supply rail and ground or between the two rails?

 

Hmmm, have you read the last few posts?

Let's back this up a bit - a few questions:

1. Are you using a single or dual supply?
2. Are you using a circuit designed for a single or dual supply?
3. Have you checked the DC voltage at each amplifier output? Are they nicely balanced somewhere between the supply rail and ground or between the two rails?

1.dual
2.dual
3. have not check, but will.

I also have 2 amplifiers for high/low pass filters, before my 100x amplifier.

 

If you are using dual supplies, then you can use the mid-point of the supplies as in your original circuit, and so dividers etc. to get an artificial half-way point are not needed.

Sorry to have laboured this point, but it seemed to me from earlier comments that you might have been trying a dual-supply circuit configuration with only one supply, which would not do.

Build-up of DC voltage along the chain may still be an issue though, so checking the DC voltages would still be a good idea.

 

If you are using dual supplies, then you can use the mid-point of the supplies as in your original circuit, and so dividers etc. to get an artificial half-way point are not needed.

Sorry to have laboured this point, but it seemed to me from earlier comments that you might have been trying a dual-supply circuit configuration with only one supply, which would not do.

Build-up of DC voltage along the chain may still be an issue though, so checking the DC voltages would still be a good idea.

right now, i am using the a dual power supply at my lab, what you saw before was probably for my alternative power supply, which gives me a dual power supply, using a battery

 

Good luck with that. I probably won't be around much longer tonight (this morning) as it's 00:30 here.

 

A 2nd-order Sallen and Key lowpass filter uses only one non-inverting opamp (not two). The input capacitor forms the 1st-order highpass filter with the resistor that applies the DC reference voltage of 0V to the input of the opamp.
The active lowpass filter must be fed from a low impedance like the output of the preamp opamp.

You said it doesn't work but you did not post the complete schematic so we cannot say anything about what is wrong.

 

A 2nd-order Sallen and Key lowpass filter uses only one non-inverting opamp (not two). The input capacitor forms the 1st-order highpass filter with the resistor that applies the DC reference voltage of 0V to the input of the opamp.
The active lowpass filter must be fed from a low impedance like the output of the preamp opamp.

You said it doesn't work but you did not post the complete schematic so we cannot say anything about what is wrong.

sorry for the messiness.
i didn't use a preamp, worked without it. so make the high pass filter inverting? i just can't get a signal after the second amplifier gaing. works well after the first with a gain of 100.

the 1st is the high pass and 2nd is the Sallen and Key lowpass filter.

 

See, I get this beautiful signal after the 100x amplifier, but not after the 10 gain amplifier.....

 

Your supply is only a total of only 9V but you use a lousy old 741 opamp designed for 30V! Maybe it will not work because some 741 opamps do not work when the supply is so low.

The 4.7uF in series with the 15k resistor to ground at the mic do not do anything and can be removed.

I can't read the fuzzy numbers but for a Butterworth filter the value of R2 should be half the value of R3 if the capacitors C1 and C2 have the same value.

The second opamp has a very difficult job trying to drive the very low 1k input resistance of the amplifying opamp. Most opamps cannot drive a resistance less than 2k ohms.

 

Your highpass filter seems to cut all the important low frequencies. Calculate it again.

 

How should we know why your x10 amplifier does not work. You forgot to post its schematic.

 

I got this working, now the problem is at the envelope detector. It is working for the higher amplitude of the s1 sound, but is not sensitive enough to detect the lower amplitude of the s2 sound. Its a simple envelope detector with 1uF capacitor and 500k resistor. Any suggestions?

 

Why don't you post your schematic?