I'm trying to build a karoke machine , but need help regarding the circuit ....
i googled it and found a circuit , but the values of passive components are unclear.
If anyone can help me with those values **broken link removed**
The top two op amps look like the resistors may be 10k ohm.
The bottom op amp apparently has more gain for the mic (40dB is typical) so it may be 2k input and 200k feedback for the resistors to the (-) input and 10k resistors to the (+) input.
All the inputs of the resistors to the (+) op amp inputs should be connected to the plus supply to bias the op amps at 1/2 the supply voltage so they can handle the plus and minus audio signal (because the op amp is connected to a single supply).
Note: Since the bias is the same for all the op amps you could just use one set of 10k resistors and connect the junction to all the op amp (+) inputs in parallel.
The microphone bias resistances (for an electret mic) are not needed. Just remove the mic coupling cap and the mic will be automatically biased from the op amp bias.
The decoupling caps between the supply and ground are 0.1µF.
Because of the op amp bias you will need to add 4.7µF dc blocking caps in series with the top two op amp input resistors and outputs. Place the plus side of the caps toward the op amp inputs and outputs respectively.