guysonic,
are you serious about your "jack extension cable"? From an EMC point of view, this is catastropic. If I can see exposed wires through the clear plastic you use, electromagnetic disturbances can see them also. Since nearly everybody now carries a cellphone, this is a real problem!
I am not kidding. I do EMC assessment and tests at work, and I have experience with recordings done in strong electromagnetic fields. Since I record steam trains, I have to live with 15kV/ 16 2/3 Hz catenaries only a few meters from my recording gear. You can bet that the combination of millivolt levels of audio and 15kV AC will expose any shielding problems seconds after switching on your gear!
The solutions I found by trial and error (I don't have a 15 kV catenary in my lab...) are those:
- avoid cheap plastic connectors and ready-made cables, especially the low-cost ones with 3.5mm connectors. The best ist just good enough. I use Neutrik: NTP3RC-B is a 90 degree, all-metal 3.5mm stereo connector with thick gold plating, a die cast housing and a strain relief that deserves this name. The price is right, I pay 3.80 Euro at
www.reichelt.de . If you are short of cash, use NEUTRIK NYS231BG (Euro 1.20). Still all-metal and gold plated, but not right angle and not as solid.
The biggest problem is getting good, reliable 3.5mm jacks. Sadly, Neutrik does not make them.
- use the cable with the thickest braided shield you can get. In unbalanced connections, hum and noise enters the recorder via voltage drop along the microphone cable. See here:
http://audiosystemsgroup.com/AES-RFI-SF08.pdf , especially Page 76 ff.
- When building adapter boxes, avoid plastic. Use die-cast boxes (Hammond, Eddystone, Bopla).
- check shield resistance from end to end of your cable. Strive for a resistance that is as low as possible.
- keep your connectors clean. Care for them.
This should result in good, undisturbed recordings without hum or noise.
Greetings,
Rainer