DIY binaural mic using Primo EM172

[darwinfriction]

I am trying to build my first DIY binaural mic using Primo EM172 capsules but I can use some advice.

What I made so far look like the following mic but without XLR connections.
Creating a DIY Binaural Microphone – Matt Davison
This is a sample recording using auto levels:

AUDIO SAMPLE

Each section is approximately 10cm long in this sketch:

(Simply 2 capsules connected to a 3.5mm trs plug)

I am using a ZOOM F1 portable audio recorder but I am experiencing more noise than expected...

I soldered the capsules using a 15W soldering iron and did not exceed 2-3s per capsule.

My questions:

How can I be sure the capsules aren't damaged by soldering or at least compare and measure them noise-wise against other mics?

My ZOOM F1 provides 2.5V PIP. I've read 5-10V would improve noise levels. What are your suggestions improving my setup and getting the most out of these capsules?

Thanks in advance!

 

[darwinfriction]

It seems like the mic capsules are ok after measuring their impedance levels using a multimeter. For some reason the section with the plug was causing interference. Replacing it solved the noise issue.

 

[Pano]

I am using Panasonic and PUI capsules on a Zoom H4n. Same 2.5V and having no noise problems at all, even thru 4 feet of unshielded cable.
Is the body of the Primo capsule tied to ground (negative)
EDIT: Sorry, somehow didn't see that you had fixed it.