ESP Project 19 with LM3876 Keeps Muting Itself

[jackand08]

Hi everyone,

I have just put together two LM3876 chip amps according to the circuit on Rod Elliots page here. I have assembled them on boards of my own design and the traces are all correct. When I power up the amplifiers with my bench-top PSU at 25v and no current limiting, the amplifiers will play music for around 5 seconds or less, then turn themselves off (when they have turned themselves off, the current draw goes down to about 10ma). This is the same with both amplifiers and happens each time the amps are turned on. My first thoughts were that the protection circuit was operating because the speaker I was playing playing the music through had a too low impedance (4ohm) so I hooked up an 8ohm speaker and the same happened again. I also thought that it could've been overheating and the thermal shutdown operating but a heat check on the chip itself and the heatsink proved me wrong. Although on Rods page it says the mute circuit was disabled I thought that this could possibly be the cause (just not to sure). BTW my music source is an iPod. Could anybody help me with this as I'm pretty baffled why it is doing this.

[XEAGLEKEEPER]

Without any source signal, do you measure any DC offset at the output?

[AndrewT]

and also check the voltage on the mute pin.

[pacificblue]

Originally posted by jackand08
When I power up the amplifiers with my bench-top PSU at 25v and no current limiting, the amplifiers will play music for around 5 seconds or less, then turn themselves off

Rm (R1) must connect with one leg to -25V. The other leg goes to LM3876 pin 8 and the negative side of Cm (C6). The positive side of Cm goes to ground. Your description sounds as if you had -25V and ground mixed up.

[jackand08]

Thanks for all of the answers, I have checked that the resistor goes to the -25v supply and the negative lead of the capacitor is connected to the resistor, however, I haven't tested the DC offset at the output. I try doing that and post the results later.