Any suggestions before building this?


2022-01-25 11:13 pm

It is a preamp circuit I made to boost mics and instruments up to line level.

I want to power it with a single 9v battery. The opamps are all NE5532.
The first part of the circuit is a high pass filter to block external DC and a buffer that also bias the signal to 4.5v. Then an inverting amp that has a max gain of 30 or 334 (depending on the switch and the 20k pot).
I also plan to use this as a kind of "saturation pedal", I added another opamp so i could clip the signal and then attenuate it. Then another high-pass to eliminate the 4.5v bias.

Im not sure if the gain of the second opamp is right (not to high or to low)... I based myself on this image:

Is 300 gain to much for a NE5532?
Could I replace the third opamp with a potentiometer? (I didnt do this, to maintain output impedance low).
Is it safe for a computer input (as long as I dont go beyond 1.22v)?

Any other advice is appreciated. It is a circuit I designed myself and it sure has some flaws...
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2011-04-29 8:37 pm
I think you'll need a rail to rail type op amp for this circuit to get enough Vpp out.
A suitable op amp would be the TLV2772CDR. This op amp can drive 600R also.

The 68R is too small and will stress the input buffer op amp.
Scale the input resistors up higher by a factor of ten or more, along with the feedback pot.

If you send the output to a computer, you can add an attenuator at the output to limit the swing.
If you get 9Vpp maximum out, you can use a 2k-1k attenuator to limit the maximum swing to 3Vpp.
Or use a 1k-1.2k attenuator to limit the output swing to 5Vpp.

To replace the third op amp with a pot (after the coupling capacitor), use a 1k to 5k pot for a small Rout.

Use a 10uF to 100uF capacitor across the battery (after the power switch).
Also use a 0.1uF decoupling capacitor at each op amp supply pin.
Also use a 10uF capacitor to decouple the voltage divider.
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