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k2panman 16th September 2012 05:11 AM

need a hand with TPA3123D2EVM -works with hand on ground
I am having trouble getting output from my preamp/amp setup. I only get good output when i stick a finger on a ground point on the amp. If I don't have my finger on the ground, I get about .1 sec of amplification out of each second - it cuts in and out repeatedly.:confused:

I have a TPA3123D2 Eval board. I am connecting a dynamic mic with a preamp to the input, in a bridge tied configuration. I am powering the preamp with a 9V battery, and the TPA board with 20 x 1.2V AA cells = 24V. The preamp -out is grounded to it's power supply. I isolated the 9V power ground from the TPA board ground. I have the preamp +out tied to +in on the TPA, and the preamp ground tied to the -in on the TPA. My speaker is tied to +R out and +L out on the TPA.

I tried lots of things to get this to work. I tied to one channel only, but I had some trouble there - don't remember what it did. The tiny little IC did get very hot to the touch and seemed to shut down at one point. The IC does have an onboard shutdown circuit if it overheats.

I suppose I can just bring a wire out of the amp and keep it in my hand when using, but I'd like to know what is happening, if anyone has any ideas.

I've attached the schematic for the bridge tied TPA. The mic preamp I don't have any info on - I bought it from a police supply website It outputs line level. Here's the info from the website:

This high gain super mini preamp and microphone is one of the smallest and best in the world. The built-in preamp features low noise, high gain and auto level adjustment by on-board IC, and line level output. This micro audio system comes with a six foot microphone lead and plug and play cable with RCA connections. The system weighs under 1/2 ounce, has line level output, requires 6-15 volts DC, and has a 1 year warranty.

Any and all comments are appreciated!

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