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Guitar Level To RCA Line Level Preamp

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This circuit brings up the -20 decibel guitar level signal to -10 decibels, which is what is required by RCA Line Level Inputs. These Inputs are found on P.A., D.J., and Home Stereo Equipment. Do not confuse RCA Line Level Inputs with 600 ohm balanced Line Level Inputs, which are also on P.A. , and D.J. equipment. The 600 ohm balanced Line Level Inputs, require an input of +4 decibels, as opposed to -10 decibels. Voltage gain of my circuit=.909×((1+(56,000/22,000)). 3.222 as shown. ( 10.16 decibels ). This is because 9.1% of my audio input signal, is buffered and applied to the inverting input of the op amp marked as 1458. A2 is the 2nd half of the 1458 op amp package. A2 also provides a buffered version, of 1/2 the supply voltage, as a ground potential for the op amp marked 1458. See schematic. Should there be any noise, on the output of the D.C. power supply, the noise divides by two, where the 10K resistors meet. That noise is coupled through the 50K resistor to the non inverting input on 1458. The noise is also buffered by A2, and applied to the inverting input on 1458. With equal amounts of noise on both inputs, there is no potential difference in noise to be amplified. Last but not least, do not connect the audio output of this circuit, to phono inputs, microphone inputs, or 600 ohm line inputs.


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  • 3 weeks later...

My apologies to the Electronics-Lab Community. I should have sent this version of my schematic for the Guitar Level To RCA Line Level Preamp. In this version of the schematic, a 5K feedback resistor is used on A2. This schematic also looks more symmetrical.


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