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Eagle CAD still has a free tier. It’s limited to 2 signal layers and 12 square inches of PCB area — both of which are sufficient for most mic circuit designs, in my experience. The interface is

Try KiCad. Best Regards, Jules Ryckebusch

My EDA software is ancient and requires keeping a 1998 Mac G4 Cube alive. I'm looking for current Mac OS schematic capture and PCB layout tools, free or low cost. What are you guys using? What's good

Very nice! Best Regards, Jules Ryckebusch

Using Jerry's idea in post #3 of using 3 op-amps, I've added a 'multi pattern' version to my collection of OPIC project mics here: www.opic.jp137.com ( http://www.opic.jp137.com ) Seems to perform

Congrats! Best Regards, Jules Ryckebusch

All good. As I said before no issue with the voltage (constant 64v occasionally -50mv). Mainly housing issue. I mean very tight space for all components and interconnections. I reflowed some solder

Also ensure you clean the PCB well especially around the 1gig Best Regards, Jules Ryckebusch

Hi Jules. I mean I was measuring the supply on its own for quite a long time several times before using it on the mic. Because it was built last (after an accident on the previous one). I will follow

Please look at this. https://www.jlielectronics.com/content/TroubleshootingOPA-Alice%20MicRev1.pdf You have something touching possibly. I write this based on my own feedback (I have misconnected

As I said I would get back with updates. I insulated both pcbs (bias- high impedance) using tape around them and I cover all the inside of the mic body with copper tape. Good signal and healthy

It should be OK as long as the unconnected wire is properly dressed as not to pick up interference. Well, it does matter, since the stray capacitance of the backplate is higher than that of the

Thanks Jerry. To start with while I was reducing cabling length I shorted either the bias IC or a cap - diode around it. When I sort that out I will try all the meters you suggested. Just a couple of

As I suspected from the start, I believe your capsules are good and the problems you had are elsewhere. >

No. It can be separate. Copper foil is OK. >

Without being sure I just used the continuity mode on my DMM. No continuity between capsules and between capsules and backplate (common backplate cable).

Thanks Jerry. Is it necessary the bias PCBs being in the same enclosure with the high impedance circuits? True. Sorry for that. I read it later. The capsule is in a mesh - the normal faraday BM 800

Head is the circuitry that receives the capsule and transforms the very high impedance into a more manageable impedance. As I wrote earlier, using shielded wire is not adequate. You have to make sure

Head is the circuitry that receives the capsule and transforms the very high impedance into a more manageable impedance. As I wrote earlier, using shielded wire is not adequate. You have to make

You can start with checking with the mulimeter that the capsules are not shorted. >