A "newbie" needs help that I hope is out there! I have a Dynaco S70 amp that hums when on alone and when connected with a PAS 2 preamp. The hum is independent of volume knob position. Tubes are fairly new. When turntable leads are added, the hum is stronger and gets stronger as volume is increased. Is there any clever circuitry device to filter out hum? -- and not lose 60/120 cycles in music coming from the turntable? And not too pricey?