Not sure this is correct, 470 ohms sounds like your measuring the wrong pad=
s?
The EM172-Z1 capsules I hacked at back in 2009 had 100R on the source to gr=
ound so unless Primo have changed the design or perhaps your using differen=
t capsules?
3 2
1
1=3DGND, 3=3DSource between 3&1 is 100 ohms on the EM172-Z1 part, if your c=
apsules
are different ignore my message entirely.
Using a fluke meter I measured 3-1 and sorted according to close results pe=
r capsules.
Then placed the (bare) capsule in a calibrator and with spring loaded gold =
contact pins
measured the sensitivity via 3V and 2.7K RL as per the datasheet at the tim=
e.
That only gets you so far. Matching for frequency response is a pretty futi=
le exercise if your time constrained plus theres not much that can be done =
to alter the response and sensitivity *at the same time* so I matched for s=
ensitivity only.
Think about it, match sensitivity, then match response from a pool of 10 ca=
psules? good luck with that one - I had hundreds at my disposal and didn't =
go for frequency response matching until the final mic assembly. Which is a=
nother issue entirely.
Let me know if I can be of further help.
BR
Mike.
--- In Peter Shute <> wrote:
>
> Mike did say to check them with a calibrator once you'd pre sorted them b=
y resistance.
>
> Peter Shute
>
> Sent from my iPad
>
> On 06/04/2013, at 8:54 PM, "Raimund" <<raimundspe=
>> wrote:
>
>
>
> > Thanks for excellent input everyone!
> > I think I will go for the multimeter-solution.
> > I am currently on the EM172=C2=B4s and getting the 470 ohm across the p=
ad 1 and 3, with a variance of 2-3 (469-472)
> > So am I right that the capsules should be within 0.1 of eachother (f.ex=
470.1 and 470.2)? If so, I need a better multimeter.
> > Secondly, if this is right, am I right to assume one would be lucky to =
get a matched pair out of a batch of ten capsules?
> > Sorry for my lack of insight BTW, I=C2=B4m working on it:-)
>
> Hi Anders,
>
> I think that John Hartog's approach is the way to go.
>
> I'm afraid that measuring the tiny differences of the 470 ohm source resi=
stor does not help here at all. I'm pretty sure the 1% tolerance of the res=
istor has nothing to do with the actual sensitivity differences of the caps=
ules.
>
> What instead matters are the specific tolerances of the internal FET tran=
sistor (its gain), the electret foil and perhaps a few geometric tolerances=
within the capsule. These much more relevant tolerances however cannot be =
measured by a simple multimeter.
>
> Regards,
> Raimund
>
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