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I would like to convert an instrument level (guitar) to a line level in order to feed the isd1820 sampler chip. What are my option in order of doing so?

In addition - I would like to mix the four isd1820 outputs (see my schematics) Using the lm358 is good choice? what are better solution? a NE5532?

enter image description here

lon_ly
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Your option is limited to having an amplifier with input stage suitable for instrument levels and impedances, and enough amplification for driving the chip input with suitable amplitude. It does not look much different than your mic or line input buffer. There are plenty of guitar amp examples you can use, even service manuals of commercial guitar amps.

For non-hifi purposes any op-amp will do. The NE5532 is used in many professional circuits as it is a very good for audio. So it's better but then again you are using lo-fi components such as ISD1820, it will not make much difference if you use an op-amp far better than what you need.

The op-amp stages you have drawn will not work, as the circuits expect a bipolar supply. Either change the circuit to work with single supply or change the power supply to proviede bipolar voltages.

Justme
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  • Will the following work for the mixing? https://imgur.com/a/PVTkZ78 – lon_ly Jan 28 '23 at 13:24
  • Please don't put external links here, as they will soon be dead. And no, the NE5532 is unlikely to work well with only 5V supply, just look at the data sheet. – Justme Jan 28 '23 at 14:06
  • I'm powering the NE5532 from the +9V – lon_ly Jan 28 '23 at 15:05
  • I agree that the ISD1820 produces AWFUL buzzer noises with no high audio frequency sounds. The LM358 is never used for audio since it is noisy, has a poor slew rate and produces crossover distortion. But both are fine for a severely distorted electric geetar. – Audioguru Jan 28 '23 at 17:07