Features 1 Power input to increase the rectifier bridge AC and DC can be used the input DC is not divided into positive and negative more convenient for using 2 Performance is more stable3 Using NE5532 op amp chip and round hole 8 pin IC socket easy to upgrade the op amp chip 4 Board size 50mm 33mm5 Operating voltage DC 9V 24V AC 8V 16VPackage included 5 x Pre Amplifier Board