SubZero Single Channel Microphone Booster

Bought the SZ-MA1 a while ago to amplify a Shure headset before feeding to the desk as the signal was v weak. It worked great at first but after a few weeks of gigging it stopped working altogether. It pass through phantom power and the signal, but if anything the signal is even weaker! Suspect I have blown something inside by unplugging it from the desk with phantom on (something you have little control over when someone else is running the mixing desk) Have taken the back off to see if there are any obvious blown/defective components. The circuitry comprises 4 transistors, 3 resistors and 2 diodes. No obvious which if them has stopped working so it's going in the bin. Shame. It looked so well built with a v strong metal case. The earthing arrangement is very suspect I have to say. There's a copper leaf spring solders onto the underside of the PCB that makes contact with the case. The paint has been clumsily/partially scrapped off by hand to allow an electrical contact, but not sure how effective it is. I can't find anything online about the differences between this model and the replacement SZ-MB1, except a change of paint colour from blue to black, plus there are reviews on other places suggesting similar reliability issues so beware and do your research beyond just amazon

Used it to boost a dynamic mic going into a focusrite Clarret 2 Pre worked great as the pres need a hottish signal

Good value for money however it's a little noisey