I have a 2-deck boom box with a microphone (input) volume control, and a mike jack; an older stereo system with a separate turntable and a receiver and an earphone jack. It seems simple enough to patch the receiver (earphone jack) to the boom box (mike jack) to record 45 rpm records onto cassettes, but the first time I tried it they came out rumbling and unclear. The second time, I had the volume control on the boom-box (mike jack) turned almost all the way down. The sound was better, but I couldn’t help feeling it should be better still. Should the volume control be turned all the way down? And the volume control on the receiver turned up high? Because of the age of the stereo system (1975) and the difficulty of finding a replacement turntable this isn’t as simple as it used to be. 
Any advice, please?
It sounds bad because you’re dubbing from an amplified line. You need to use a line in and a line out. You can get a replacement turntable at most Best Buys.
Sorry if this doesn’t help.
–Tim
Thanks… 
It’s a Sylvania receiver and a turntable compatible with it, if that’s any help… Garand or Garamond or something like that…
Long after I started this thread I connected the input wiring to the “AUX” jacks on the tuner and recorded with the tuner set to “AUX”; mike volume low; tuner volume high, with a headset hooked up so as not to disturb our neighbors. Patch cord was connected to the tuner headphone jack and the boom-box microphone jack. This provided a master tape to make recordings from, and the fidelity of the recording was quite good.
However, I like to add my comments onto a recording. Using another tape player with a single headphone jack, and my boom-box with a single microphone jack, I plugged the other end of the patch cord into a Y-connector along with an exterior mike. The only disadvantage is that my comments on the mike don’t seem to get recorded. Well, I’ll keep at it…