Sunday, March 17, 2013

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Portable Phone Preamplifier

Portable Phone Preamplifier

This unit was designed for fans to have an old vinyl record collection and willing to be digitally remastered on a personal computer. Or sometimes you can hear an old collection of priceless LP, through its modern hi-fi, usually without a preamp stage: this is a circuit capable of meeting their needs. The unit is powered by a 9V battery, allowing for quick and easy connection to all the pre-amp high level input and drawing very low current circuit ensures long battery life.

Despite the low voltage circuit performance with moving magnet pick-up is quite good, with high input overload capability, very low distortion and accurate reproduction of the RIAA equalization curve, thanks to one of two stages of the operational amplifier circuit in which the RIAA equalization network is divided into two halves: an input stage of the application of low-strengthening the RIAA equalization curve in a cable series feedback configuration and a second stage, the application of the acute curve cutting through a second operational amplifier connected to the shunt feedback configuration.

Battery operation is also minimized the possibility of hum pick-up, a potential danger is always present in a high gain, high sensitivity phono preamps. As the drawing of the total circuit current is 1. 2 mA when powered by a 9V battery, the use of an LED lamp will be the main cause of current consumption. Therefore, a very small, low current red LED recommended for this purpose. With a resistance of 6.8K limit specified for R11, the LED will draw an additional current of 1 mA, it will not shine, but can still be easily seen.

A typical carbon-zinc 9V battery will allow the circuit to operate about 180 hours, while an alkaline battery will last over 250 hours. If the LED is omitted, the duration is almost double. In any case, for those who wish to preserve the battery, the circuit can also be powered by a common external adapter power supply, valued at about 12-15V DC, 10 mA or higher. In this case, the input circuit overload will increase even more.

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