I hooked the electret board to a pair of 25mm capsules via a DP3T ON-OFF-ON switch to give three pickup patterns, Cardioid, Omni, and Fig-8 (see articles on 3-pattern electrets for how-to).

The two boards with polarizing oscillators were given SPST switches and 34mm K-12 double-side capsules, for Cardioid and Omnidirectional patterns.

Since theoretically a non-polar electrolytic capacitor exhibits less harmonic distortion than a polarized one, I measured the ‘plain’ circuit with Homero’s polarized output caps, then changed them to non-polar audiophile types and re-measured. Those are the green ones in the photo above. It made a barely measurable difference. These op-amp mic circuits are super clean and distortion free regardless.


The tube emulator works; that is, it adds harmonic distortion like a tube or JFET, because the signal is run through a carefully biased JFET. I am a bit perplexed at the idea. If you want that kind of distortion, why not build a Schoeps or KM-84 circuit which ‘naturally’ offers that kind of harmonics?


I want to do further research and testing of op-amp circuitry, and it’s been added to the list of things to try. The op-amps have been in short supply recently. Hopefully they will come back in stock at distributors soon.


Regardless, thanks to Homero and Jules for the chance to try out some of their circuits. I wouldn’t have gotten around to building OPA mics this soon. Test results in the next article.