After making a couple of mintiboost kits I've been keeping my mint tins of various sizes in the hope I'll be able to use them as small project enclosures. The first I'm trying is this Collin’s Lab: DIY Contact Mic
which is a simple enough circuit that works fine outside of the tin. But when I mount it in the tin, the gain on the little amp drops back to mostly terrible, with bursts of unbearably loud (granted the guitar amp is turned up to 11 to compensate). There are enough metal enclosures out there (my guitar pedals even) in audio that mean I have hope it should work.
I expect this is something to do with grounding the tin, since the 1/4" jack for the amp is mounted through it, as is a 3.5mm jack for the contact mic. I've experimented with additional earth wires mounted to the tin itself but so far am not improving things. But take everything out of the tin, and have the jacks out in the air and all is fine, all the time.
The threaded part of these jacks is also the earth, thus my thoughts it is an earth thing. So my question is - what is likely the cause of this, and what should I be doing to dampen this effect...and is there something you can point me at to read up on why my experiment of directly wiring the tin to the circuit's GND isn't helping?
Thanks for your advice, Geoff