pmr@drutx.UUCP (Rastocny) (07/25/85)
[] > It's very easy to do it yourself and all you risk is one audio patch > cord (even I can afford that). To see if this is your problem, take one > of the interconnecting shielded cables (the one which when you connect > it, the amp hums). Examine the area where the connector joins the cable > at the end away from the amp (the other end, the preamp end). With a razor > or other sharp object carefully cut away the outside cover <and> the shield > wire, leaving undisturbed the inner conductor and the insulating material > around it. You may wish to wrap the operation site with some insulating tape > to keep the shield from unraveling further and provide some more mechanical > protection. Now plug the cable back in. If the hum stops you have your > answer. I will try to draw the cable as it should look when you are finished: > > > - ----------------------------------------- > / \ > ooooo--------------------------------------------oooooo > \ / > - ----------------------------------------- > > ^ > Shield > interrupted > here > Preamp end of cable Amp end of cable > > > What perhaps you should do is treat both cables from amp to preamp > this way and provide a separate ground wire return path via a fairly > heavy wire. Real purists will make all interconnects this way - single > ground wire. Big danger is that if that ground wire should come loose, > you have one fine lot of hum from your speakers (just before they > vaporize). > Good luck! > > Dick Grantges hound!rfg > > "It's the thought, if any, that counts!" Dick Grantges hound!rfg Close Dick, but no cigar. The cable should have the shield connected at the source (preamp) and not at the destination (amp). That's what the arrows are all about (re: original article). Dick's idea works fine. I use this method on my own system with Monster Interlink and between my mixing console and tape deck. - ----------------------------------------- / \ ooooo--------------------------------------------oooooo \ / - ----------------------------------------- ^ | Shield interrupted here Amp end of cable Preamp end of cable Another related item that causes hum/noise is AC line phasing. Your stereo equipment can all be properly phased to reduce this phantom noise with the following procedure. Unplug the interconnects between all of your equipment. Connect a good microammeter or oscilloscope between chassis ground and 3rd-wire ground (or a water pipe). Next, reverse the equipment plug polarity one piece at a time, beginning with the preamp, until everything is polarized to its lowest chassis leakage. One last noise source is inter-equipment magnetic coupling. The power transformers used in some audio equipment are either not magnetically shielded at all or just not well shielded. This magnetically leaky equipment should NOT be placed near low-level amplifying circuitry (like the phono preamp). Physically moving the leaky piece of equipment is the only inexpensive solution for this problem. Yours for higher fidelity, Phil Rastocny AT&T-ISL ihnp4!drutx!pmr