Hum and noise in microphone

Dear all - I have done extensive searches here but am getting slightly confused with the reason for ground loops in a microphone project I am building. I have gutted a chinese tube mic and power supply and am doing the following:


1) The circuit I am building uses a Telefunken EF12 tube, of which the components requiring ground connection have been soldered to the pin on the tube socket that relates to the tube's heater's ground pin.

2) This heater gorund pin is connected to the 0v wire which in the 7pin mic cable is pin 5. At the mic's cable socket, Pin 5 (0v Cable), pin 7 and the socket shell (flat pin "8" if you like) have been internally connected. The mics body also appears conduct with these pins so must be connected by touching the socket shell.

3) At the power supply, the mic cable socket has 0v cable connected connected to pin 5 and just like the mic socket end, pin 7 and  shell have also been connected internally. The shell of the seven pin mic cable socket is wired to the shell of the 3pin mic cable socket and the shell of the 3 pin socket is wired to pin 1 (shield) of the 3 pin socket of the other cable that goes to the preamp etc.

I simply cannot find where the ground loop is occruing and creating the aweful hum

Any assistance would be greatly apprecaited.

thanks

When you are testing the microphone, do you have it completely assembled including the head shell?

ah well the head basket is on but the mic body isn't.  The nose is almost as loud as actual audio signal. Would attaching the body fully reduce it that much?

yes - you absolutely need total electrostatic shielding when testing such electrostatic-based circuits..

Jakob E.

Ok I put the whole thing together and guess what? - no noise!

I feel embarassed for wasting your time with such stupidity Jakob and Burdij.

Thanks

Hi deuce,
Just FYI, this was not a ground loop. This was electrostatic hum pick-up, due to the absence of ...electrostatic shield.
Many people use the locution "ground loop" for a hum problem, just as others use "digital overload" for any kind of overload or clipping, and many use "hum", "buzz" or "hiss" for any kind of noise.
A ground loop is not a symptom, it's a cause. It generally causes hum or buzz (which are two distinct things, hum is essentially a "clean" sinewave at mains frequency, buzz is a signal at mains frequency, which contains a noticeable level of harmonics, which make it more unpleasant).
Hiss is perceived as a high-frequency wide-band noise, which in fact contains all frequencies distributed more or less evenly. Note that "noise" in semiconductor spec sheets refer to that kind of noise (hiss), because they don't produce hum, buzz or any pitched noise intrinsically.
A microphone is almost immune to ground loops, unless its body touches a grounded metallic part.
Please don't think I'm lecturing you, but I have seen some threads going all sorts of false tracks because of the use of incorrect words to describe the symptoms.
And we can start a heated debate about "pop", "click", "chirp", "motor-boating",...

No abbey road no lecturing taken at all. I am glad to understand and learn as much as I can. Thanks for your insight. Thats what makes this place great.

Cheers