Tuner Interference

[foetusized]

I switched amps in the bedroom system last weekend, and after getting everything hooked back up I started trying everything out. While testing the tuner, a Pioneer TX-610, I switched it to AM (something I hadn't done in months) and it produced an ugly squall all across the dial. I'd made several changes in the past few months (speakers, a DT-510 timer, the TV sitting on a chest of drawers right behind the stereo) and hoped that the problem was interference and not something fried in the AM circuit.

Yesterday evening after getting my daughter to bed, I started moving stuff around upstairs to see what the problem was. Long story short, after a couple of hours I made several discoveries.

The cheapo AM loop antenna I had bought at a Salvation Army thrift for 50 cents is a definite improvement on the small internal AM bar antenna inside the TX-610.
My Pioneer TX-608 (basically a TX-6800 with a black dial) is not only too tall to fit in the space where my TX-610 sits, but I thought the sound was thinner than the 610.
The cheapo Apex DVD player was causing the interference. I've had it sitting on the tuner since the TV change back in April, but hadn't had the tuner on AM to discover the problem. The interference was different depending on if the DVD player was on or off, but either way the AM was unlistenable.

I then managed to move the DVD player over to the opposite side of the TV, displacing a stack of my wife's books that didn't need to be there. Everything's back to sounding great.

I guess my question is if this type of interference is common, and why is it happening even when the DVD player is off? -- Foe

[gearhead]

This is just a semi-educated guess, but most things like CD players and DVD players aren't really "OFF" when they're off, they're on standby.
If they're plugged in, they're on.

[Micropassatman]

I have the same problem in my bedroom. When DirecTV installed the Samsung TiVo PVR, my AM reception went to Hell.

[foetusized]

That's right, gearhead. The DVD player can be turned "on" from the remote, which means the IR receptor has to stay on all the time. Didn't think of that, thanks -- Foe

[OvenMaster]

In the 90's, when I used a RadioShack DX-440/Sangean ATS-803 Shortwave portable, I got all sorts of interference from in-house dimmers. The only way I got rid of it was to use an outdoor wire antenna, fed by a piece of coaxial cable, and grounding the shield to a water pipe. Since my Yamaha T-80 is right next to a Sanyo VCR that causes the same problems mentioned above, I think I have to try the same trick again. Thanks for the reminder of this phenomenon, guys.
Tom

[markthefixer]

Try to kill the interference at the source. Rat Shack has a "filter" that the power cable wraps around/through. Basically a ferrite "choke". Grounding the device if it is a metal case MAY help. Can wrap the interconnects through a similar transformer to cut radiation on them but a quick test would be to disconnect them while doing the power line/grounding stuff.
Sounds like a 455 khz (am if freq) problem, just bad luck to hit a "sweet spot".

Radio Shack info: "Snap-together ferrite Choke Core" $5.29 #: 273-105

Shortwave recievers are the best/worst way to find interference/radiation as the FCC part 15 interference rules may cut it down, but to the really sensitive stuff (am/sw Sometimes fm) it comes blasting in.

As a sidenote, the electromagnetic fog we live in is getting worse and so will the interference.

[dr*audio]

Most modern VCRs and DVD players have a switching supply, instead of an analog supply. these new pulse modulated supplies are more efficient and have a very small and lightweight transformer so they save on cost and shipping weight. But they switch at 50 - 100KHz or so, maybe higher, and the harmonics generated by the switching pulses must fall right in the AM band. You can try the ferrite core on the power cord of the noise source. You can buy ones that clamp over the cord, or buy a large ferrite doughnut and wrap the cord thru it a bunch of times. Computers and monitors also cause interference; in the FM band, too! I have to turn my computer off when I do an alignment or I pick up stray signals from it.