The gain is set by the feedback resistors, and is independent of the supply voltage, until it drops below a useable level - when you will probably get high distortion.

Originally Posted by Nigel Goodwin

The gain is set by the feedback resistors, and is independent of the supply voltage, until it drops below a useable level - when you will probably get high distortion.

will 3130 or 3140 will reduce battery consumption?

Put a socket in and try using different IC's, personally I find it's usually impossible to hear any difference.

The TL072 and LM833 are shown on their datasheets with a supply voltage as low as 10V. The TL072 has a minimum supply of 7V which is more than a weak 9V battery can supply.
The NE5532 has a minimum supply voltage of 6V which is a dead 9V battery.

The LM4562 dual opamp has a distortion of only 0.00003%, very low noise and a minimum supply voltage of 5V. But its supply current is typically 10mA.

Thanks everyone. Sort of fun to do something a bit different.

Originally Posted by Nigel Goodwin

Put a socket in and try using different IC's, personally I find it's usually impossible to hear any difference.

Did a little PCB with and socketed the opAmp. I tried to get the gnd plane between most traces.

Edit: added schematic, mostly the same as the original.

Audioguru: The mike element I am using came in a grab bag from RadioShack that I picked up 10 or 20 years ago. Not sure that it would pay to toss a high end opAmp at it. I may look for a better mic if I am unhappy with this one.

You use only one opamp but are using a TL072 dual opamp.
Why not use a TL071 single opamp?

Originally Posted by 3v0

............... I have to wait till the AM to buy a 1/8 plug so I can try it with the computer. It does drive a headphone, sounds clean. Hope it stays that way when I attach it to the computer.

I will be powering the circuit using a 9V battery. A 10K audio taper controls the output level. I would like to replace it with two fixed resistors. Will the output level be fairly flat/steady over the life of the battery? Or do I need to adjust the output level as the battery ages?

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If you ara using the MIC input of your computer´s sound card, there is usually a DC supply available in the "ring" (middle) contact of the plug.

You may try to use it and eliminate the battery (and its aging problems )

An electret mic has a supply current of only 0.5mA. The power from the input of a sound card supplies it which is not enough to power a TL072 preamp circuit.

The output level from the opamp will not decrease as its battery voltage drops, the distortion rises instead. It will have crossover distortion then clipping distortion.

Originally Posted by 3v0

It is working with a 9V battery but the TL072 does not have as much gain as I would like. If both the PC and preamp are set at max it is just enough to make it work fairly well. Might be nice to have some headroom.

The voltage gain of the preamp is the ratio of R4/R6 plus 1. Its gain of 23 is very low for a mic preamp. Remove your 5pf capacitor and increase R4 to 150k for a gain of 101. 330k gives a gain of 221. 1M gives a gain of 668. You can have as much gain as you want.

The little mic/preamp background noise was very low when I checked it with a headset. When I feed it into the sound card it was noisy. It was picking up noise from a nearby flash drive.

Computers are designed by logic experts. They don't know about audio circuits.
I fed my electret mic directly to the mic input of my Compaq 486 pc and it was excellent. The sound circuit was part of the motherboard.

Do you screw up the supply from the sound card if you insert a mic with a mono plug?

A microphone input has a very low current for an electret microphone. The input will overload if it is fed the output of your mic preamp. You should feed your mic preamp to a line input of your sound card.

The 3130 and 3140 will not work with the current PCB. Not that it is a big deal to make a new one but I would like to see if it will work as if first. Thanks for the suggestion.

I have heard that the very old CA3130 and CD3140 are extremely noisy and are not suitable as a mic preamp.