Ferrite and power line filters?

[crumhorn]

^^^
That's not the problem then.

[Tone Deft]

the battery powered mixer is the problem. it's an ungrounded amplifier on an antenna. if it has a grounding lug, ground it with that, otherwise power it with its own power supply.

[gurumonkey]

the battery powered mixer is the only way i've gotten it to work, but only with the 8" cable. using the profire i have yet to be successful in moving a clear signal into the mic input on the mac mini.

i'm trying to do a test now to see i have this working, but i have no skype contacts online who can do video right now.

[gurumonkey]

Ferrite came today. used it in several places. nothing.

but to test the ferrite i connected my mac mini directly to my receiver, which was picking up radio and ground hum like CRAZY! i learned that it did not matter if put ferrite on, but i did learn that i am indeed picking up an AM radio station (either 1440 or 1220, simulcast). i also discovered this little tidbit. while trying to apply the ferrite to the cable i had going out, i realized that when i moved the cable sometimes the sound would go off. i wondered if possibly i had a bad cable, so i test to see if the signal would still come through. answer is yes.

so now i have discovered that there is some kind of grounding problem inside the mac mini with the headphone jack and microphone jack. however, i have no idea if there's anything i can do about it. i've taken apart the computer before, i could do it again.

anyone have any ideas?

[blakbeltjonez]

using ferrite cores properly can be tricky - you usually will need multiple in order to achieve threshold impedance (the inductor impedance usually needs to be several hundred ohm to start to be effective against VHF and UHF frequencies), and the RF rejection increases as the square of the number of turns of the cable around the ferrite loop/core/etc.... so, one turn = fucking useless, 10 turns is a world of difference. you'd need a few snap-on cores to effectively eliminate an RF issue, since you are relying on the physical coverage of the inductor along the cable rather than the cable wrapping around a ferrite loop.

i ran across an interesting paper on audio applications..... it gets kind of hairy with theory, but there's a lot of valuable info

http://www.audiosystemsgroup.com/SAC0305Ferrites.pdf

edit: have you tried to AC ground lift the power supply to your Mac Mini? if you have hum going on as well, you definitely have a ground loop in your setup somewhere.

[leisuremuffin]

move your shit a few feet in any direction and see if the rf interference goes away. this will work.



.lm.

[blakbeltjonez]

move your shit a few feet in any direction and see if the rf interference goes away. this will work.



.lm.

that may or may not work, depending on how strong the offending RF signal is and how it's getting into the audio. i used to run into severe RF problems in a performing arts center that was not far from an AM transmitter...... it was hell on certain guitar and bass amps, physically moving the gear made little difference. using cables with a full braid & foil shield (TS 1/4" cables made from Canare Star Quad) helped keep the amps from speaking Spanish too loudly...

a well shielded high quality cable in the right places will go a long way in preventing RF... and crappy AC ground seems to always go hand in hand with AM radio RF problems

[stonee]

in the right spot in my freinds house, with the right amp, I can use a wah pedal as a radio tuner...

[SubFunk]

it's generally not a bad idea to use powerstrips with a RIF (radio interference filter) for audio equipment.
they are not that common most powerstrips only have a surge protector... but they are around and not to pricey.

i use one at home and it certainly helps to reduce (not totally eliminate) the all over noise.