Regenerative Echo on iPad by connecting a capacitor between headphone ground and mic hot pin

At your own risk.

Various values of capacitors were connected between headphone socket ground and mic hot pin on iPad mini air 2? The latency gives Echo and the capacitor gave regenerative echo (feedback, feeding back from headphone out to mic input). This gave a really interesting sound recording singing voice.

This came by accident while connecting a Heathkit box of capacitors to low cut high frequencies on the Pleiades K177 preamplifier inside the Tuchel connector for the MD421 HL mic. Various capacitor values were tried in order to compensate for voice effort and Fletcher Munson curves on the high frequency part of spectrum. 

The echo became apparent by chance by the clicking sound of the capacitor switch. Feedback can be adjusted by iPad's headphone volume until positive feedback takes over!

Amazing sound, analogous to the multiple selfs seen if you watch yourself between parallel mirrors. Electromagnetic waves bouncing which is really the same thing.

22nF for example gave nice results including reduction of any hiss from ambient noise.

The echo energy is low cut as ther is a capacitor involved in series. It is also high cut as the capacitor is between JFET drain and ground.

Setup:

Singing male voice Somewhere Over the Rainbow - 1 to 1.5in from mic - Sennheiser MD421 HN (LC low cut) - Pleiades K117 inside Tuchel connector - 3m video red cable - iPad (22nF between headphone ground and mic hot), GarageBand volume at 7, headphone volume at 7 - Sennheiser HD 580