Has anyone ever used one of these? They are available on eBay for only $20 Also a reference link: http://www.w3am.com/8poleapf.html Power Supply: +/- 5VDC to +/- 18VDC ( < 200mA ) Recommend best +/- 15VDC Input Impedance: 5.5k OHM ( at 1kHz Sine wave ) Input Level: 2000mV RMS ( at Power supply +/- 9VDC). 2500mV RMS ( at Power supply +/- 12VDC). 3000mV RMS ( at Power supply +/- 15VDC). Frequency Response: 10Hz - 100kHz ( -3dB ) .