Microphonic Metalized Polyester Caps

[Greenballs]

...

[duck_arse]

are we awaiting further input on this topic, or wanting thread deletion?

[iainpunk]

thread of the year

[danfrank]

Yes?
No?
42...

[ElectricDruid]

I'mmmm.....spoooo....druuuuu..nnnnkkk.....

[idy]

Is that a Microphonic Metalized Polyester Cap in your pocket or are you just happy to see us?

[fowl]

Is that a Microphonic Metalized Polyester Cap in your pocket or are you just happy to see us?

Maybe a little of both?

[anotherjim]

I remember it when it was just a query. Then before you know it, it's a fully grown enigma.

[Greenballs]

Nothing to see here...

It was a great query, you guys totally missed out. Unluckily for you all, I sussed out what the issue was before you all got to dedicate time out your day to helping some guy you've never met in person on an online forum. This one had the potential to run for weeks too...

Maybe next time!

[amptramp]

Something else to add to the Burst Box.

[iainpunk]

Nothing to see here...

It was a great query, you guys totally missed out. Unluckily for you all, I sussed out what the issue was before you all got to dedicate time out your day to helping some guy you've never met in person on an online forum. This one had the potential to run for weeks too...

Maybe next time!

so.... what was the whole deal? what about those microphonic metalized polyester caps?
i really want to use an odd microphone type for my next microphone project.

cheers

[duck_arse]

Nothing to see here...

It was a great query, too...

Maybe next time!

photos - or it didn't happen.

[amptramp]

I have run into microphonic flexprint leads before in a project where 25 megohm impedance was maintained over a large number of channels.  The flexprint led from InSb infrared light sensors to transresistance amplifiers with a "gain" of 25 megohms.  (A transresistance amplifier is an op amp with a feedback resistor from output to inverting input with the signal source connected directly to the op amp.  A current input provides a voltage output with a gain equal to the resistor.  A transresistance amplifier keeps the voltage across the sensor fixed (at zero) for best linearity.)

There was a Kapton (polyimide) flexprint going from the sensors to the amplifiers and we were getting noise from it.  If you look at the equation:

CV = Q = iT

where
C is capacitance
V is voltage
Q is charge
i is current
T is time

It is apparent that a change in capacitance has the same effect as a change in voltage across a fixed capacitor and we were getting current from the flexing motion of the flexprint due to vibration from the refrigeration unit connected to the sensors.  I have not heard of polyester being microphonic before but certainly ceramic is microphonic and maybe some versions of polyester are also.

[iainpunk]

"all capacitors are microphonic, but most types have an output potential which is dwarfed by any resistors thermal noise"
- Peter (paraphrased and translated by me, also forgot his last name as we always addressed him by a nickname)

it really reminds me of my capacitive guitar pickup which never got off the ground due to sounding really bad (an undefined muddy mess with some power supply whine)

cheers