Re: Noisy Cricket MkII

Posted by induction on Mar 12, 2014; 5:16pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/Noisy-Cricket-MkII-tp8503p8523.html

It was because the IC was heating up, especially since it only happened when you had something plugged into the input and output.

The thing that heats up ic's, especially power amp chips, is current. Pre-amps are designed to amplify voltage, but power amps are designed to amplify current (the 386 actually does both). The amount of current (I) through the chip depends on the output load it sees. Higher impedance (Z) loads reduce the current at a given voltage (V) accoarding to I=V/Z, so they produce less heat. If you short the output, the impedance goes way down, current goes way up, and the chip will get really hot. (Higher power chip-amps run much hotter and almost always need to be heat-sinked.)

I suspect your defective jack only shorted when a plug was inserted, otherwise the chip would get hot with nothing plugged into the output. Sometimes the connectors can rotate until the lugs or connection tabs touch. The same thing can happen if you use a stereo jack and wire the signal to the ring instead of the tip. Likewise, if you wire the signal to the tip, and ground the ring, the chip will overheat when nothing is plugged into the output.

Glad you got it working.