Dear Nature Recordists,
Thanks for the opinions !
Rob said :
> Also sounds like a faulty capacitor-- a problem my mkh-30 developed
over time.
Yes, several people told me that.
But I don't know why Sennheiser Germany decided to change the capsule.
They didn't mention that they changed a capacitor...
Rob said :
> The capsules are oscillators. Could be interference,.. if something
isn't working correctly.
And Mike said :
> Could this be a "beat note"? Interference between the RF oscillators
in the two mics.
> If one runs at 10,000,000 Hz and the other one runs at 10,010,000 Hz,
then the "beat"
> will be 10 kHz.
Yes that was what I think, because moving the microphones closer
together was like playing theremin, and aluminium foil between the two
caspules (just the head of the microphones) stopped the interference.
The signal was appearing only when MKH30 and MKH40 were 6-7 cm close.
When they were more distant, they worked correctly.
But why and how can this electromagnetic go trough the grid and metal
body of the microphones ??? They are supposed to be protected against that =
!
Anyway, since I leave in one week for a one month trip, with the help of
my father (who is electronician - but not specialized in microphones...)
I opened the MKH 30...
Very impressive to make this kind of diy surgery... :-/
The circuit of MKH microphone have two ferrite coils. I slightly modify
the tuning of the closest coil to the capsule, while listening to the
signal. Moving it a very very little bit, the frequency of the
interference was getting higher. I tuned it until I couldn't listen to
it (above maybe 18.5 kHz : my ears and headphone work until there), but
I could still see the signal on the led of my SD722. A little bit above
and it disappeared (the preamp of the SD722 is given for 40kHz).
So know I have probably a very high frequency interference that is
filtered by my SD722, and after a few tests of my setup, it seems to
work correctly. I'll try it in the field (this weekend with Hyla
meridionalis and next week in Estonia...).
But I still don't understand exactly the whole story....
Anyway, if anyone has ideas or advices for the future...
Friendly,
Yannick
--
www.kalerne.net
www.yannickdauby.net
current location : vence, france
next location : mooste, estonia
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