Top Gun SP-1a Speech ProcessorThe SP-1 was the original speech processor designed by Clear Channel Corporation for their AR-3300 radio. It was developed to improve the low FM modulation of that unit. When they installed the first SP-1 in their radio they immediately realized the benefit in FM,AM, and SSB. It gave the radio and audio punch that sounded great. This was an option on the AR-3300-25, AR-3300-100, AR3500-25, and the AR3500-100. It was the most popular option out of the four options available for those radios.Later came the SP-1a a smaller and improved speech processor. It has a compression adjustment and an input gain adjustment as well. The unit is completely shielded in tin or in the later units a brass enclosure. The design incorporates RFI filtering on both the input and output. It had a relay that switched the SP-1a completely out of the circuit. With it off you can operate the radio with no added amplification or tone change so you can truly hear the before and after when you switch it ON and OFF.The SP-1a works well in most any radio that it fits in. It connects between the mic jack and mic preamplifier input. It picks up ground from the mic jack ground pin. It can be switched in and out of the circuit connecting the gray wire to a ON/OFF switch and the other side of the switch to ground.After the AR3500 was discontinued, the SP-1a was sold and became the property of Top Gun Technologies. They still manufacture them here in the USA.