Basic Valve Mic 101 Question

[deuce42]

At the risk of asking the inane - I am kind of new to building mics;

I am putting together a valve microphone design around a Mullard CV4031. My first attempts with a second hand professionally reskined
Neumann K87 capsule were pretty horrible. Not much bass or treble and the mic sounds kind of "distant".

Then it occurred to me:

1) I have read that the capsule on a valve mic usually needs to sit very close to the head amp because of the high capacitance,
2) Wires on a condensor capsule are also usally pretty thin and fine.

Is there a reason for this very fine wire from the capsule and does it need to be very short so as to not degrade the signal coming into the head amp?

My thinking is one of my problems may be too much wiring I have inside the mic. I have connected some 2mm thick hookup wire between the fine capsule wires and the rest of my circuit (as the fine capsule wires werent long enough to reach my circuit) and I also note that my xformer (cinemag 2461 nico) wires are quite long.

Anyone have a guess that wiring may be contributing to the problem?

The circuit is a common one and presumably the capsule should be alright if not great. Tube's been used in other circuits without a problem.

 

[zebra50]

I don't know that tube but it could be a number of things - can you post up at least the circuit?

The bit between the capsule and tube is indeed the critical area.

Is your transformer connected right? Sounds like you might be phase cancelling something.

 

[Gus]

You need to troubleshoot.  Divide up the build and test the separate parts.

Do you have a known good microphone?  If so install the reskin in the working microphone to test the capsule. 

Test the tube.  Take voltage measurements of the plate, cathode, heater and middle of capsule voltage divider.

Check that you have the transformer connected correctly.  If installed backward you will have a very low output to no output.  Red and Brown to tube, Yellow and Orange out?

Next do you have a scope and signal generator?  Do you know how to test a transformer?

A picture would help with your other questions, can not give good help not knowing how the wires etc are run and connected.