Sony CCD-FX620 microphone too sensitive.

[David Farber]

A while back I replaced the left and right microphones on my Sony CCD-FX620
thinking that would help clear up the audio distortion when recording a video.
Of course, that didn't help much but replacing the smd caps did fix the
problem. Everything is ok now except the microphones are picking up noise like
a sensitive stethoscope. Each left and right mic contains two small mics that
face each other. I have a feeling that when I removed the original mic's, there
was some acoustic insulation material that had to be removed to gain access to
the screws that were holding the mic's in place. When I installed the new
mic's, I don't think the old material was reusable. I didn't think much of it
at the time but now I'm beginning to think that this is causing the problem.
When you put on headphones, it's very easy to hear the mic's picking up the
normal drum motor noise. My old tapes don't have that noise recorded on them.
Is there some special insulation material that needs to be inserted in the mic
holders? Perhaps behind the microphones? I tried putting some foam material
between the back of the mic holder and the front of the camera but that didn't
make any noticeable difference.

Thanks for your reply.

 

[Mike]

a sensitive stethoscope. Each left and right mic contains two small mics that
face each other.

The shield stuff is probably just foam to keep wind and dust out of the
mics. This won't make the mics more sensitive in the way you describe --
it's absence will make wind noise more objectionable. Try and find a
suitable foam replacement. Codge something together from a standard foam
mic-protector if necessary.

If your mics really are *each* made of 2 small mics facing each other, that
is, 4 mics total ... it sounds like they are being used to do noise
cancellation or directional control of the sound (like a wide-tele zoom
setting). The original positioning and wiring of the mics would be
important. It is possible to create cardiod/hyper cardiod patterns by
sticking 2 capsules back to back and then "mixing" the resultant signal.

[If you've ever seen studio mics with the omni/fig 8/cardiod switches, that's
one way they achieve it]

Did you wire the new capsules in *exactly* the same, and are you sure? The
wiring of the old ones may have been counter-intuitive, and you've
accidentally wired the new ones "intuitively", if you get me.

Did you get them in the right physical locations?

Have you mixed and matched old capsules and new, or replaced wholesale?

Have you still got the old capsules?

Any details on how the mics are wired (series, parallel, their own separate
inputs etc.) ?

Mike.

 

[anonymous]

a sensitive stethoscope. Each left and right mic contains two small mics that
face each other.

The shield stuff is probably just foam to keep wind and dust out of the
mics. This won't make the mics more sensitive in the way you describe --
it's absence will make wind noise more objectionable. Try and find a
suitable foam replacement. Codge something together from a standard foam
mic-protector if necessary.

If your mics really are *each* made of 2 small mics facing each other, that
is, 4 mics total ... it sounds like they are being used to do noise
cancellation or directional control of the sound (like a wide-tele zoom
setting). The original positioning and wiring of the mics would be
important. It is possible to create cardiod/hyper cardiod patterns by
sticking 2 capsules back to back and then "mixing" the resultant signal.

[If you've ever seen studio mics with the omni/fig 8/cardiod switches, that's
one way they achieve it]

Did you wire the new capsules in *exactly* the same, and are you sure? The
wiring of the old ones may have been counter-intuitive, and you've
accidentally wired the new ones "intuitively", if you get me.

Did you get them in the right physical locations?

There are two ways to install the mic pairs. That would be either facing
toward each other or facing away from each other. I installed them facing
away from each other because it made more sense to have them facing the wind
screen where the sound would presumably be entering.

Have you mixed and matched old capsules and new, or replaced wholesale?

Have you still got the old capsules?

The picture at the link below shows the new capsules and they are identical
to the old capsules.

Any details on how the mics are wired (series, parallel, their own

separate

Each pair has its own four pin plug. The pc board wiring connects the two
mics in parallel. The net result is that you have two left mic's, two right
mic's, and each left/right pair in parallel.

inputs etc.) ?

Mike.

The new mic's come prewired with connectors that match the PC board
connectors. Each microphone pair is in a metal casing which itself is
encased in a rubber fitting. Here is a link to the picture.
http://www.pbase.com/image/39324113/original

Thanks for your reply.

 

[Mike]

There are two ways to install the mic pairs. That would be either facing
toward each other or facing away from each other. I installed them facing
away from each other because it made more sense to have them facing the wind
screen where the sound would presumably be entering.

Ah, now that doesn't answer the question: Did you do it the *right* way?
What makes sense (intuition) isn't necessarily right ... You need
to look at how the old ones *were* fitted -- if you've forgotten you could
always swap them and try them the other way (facing inward).

Each pair has its own four pin plug. The pc board wiring connects the two
mics in parallel. The net result is that you have two left mic's, two right
mic's, and each left/right pair in parallel.

Interesting. It is possible that the spacing between the pairs has been
designed to reject the "whine" of the mechanism. I recently read some
old articles where a company had patented this idea. The mechanism made
nasty noises all the way up into the 2.5KHz region, objectionably placed
in the audio band. They designed the mic spacing to reject these frequencies
coming from the mechanism to get it under control.

British Patent 2031690 (or see Practical Electronics Oct 80) and British
Patent 2104344 (or see Practical Electronics Nov 83) has a directional
system using 4 mic capsules -- patent by Polaroid.

The new mic's come prewired with connectors that match the PC board
connectors. Each microphone pair is in a metal casing which itself is
encased in a rubber fitting. Here is a link to the picture.

So it's a straight remove and refit, limiting the possibilities of a
simple wiring cockup?