AMP11 blown up. Any ideas?

[MickB]

Whoop! I've managed to revive the second failed amp! When the first board failed I replaced the blown TP2050 with an STA516B at Krilli's suggestion, and when that didn't work I fitted a new TCA2002 as well. That didn't work either and the board was still dead so I gave up on it. There was nothing to lose though so I decided to desolder the chips and use them to replace the blown chips on the second failed board, and much to my surprise it works! I now feel ridiculously pleased, it's even more satisfying than building a new board from scratch

So I've got a working amp fitted with an STA516B. Now it's just a question of whether I can fit any sort of protection to avoid it blowing again, or whether the beefier power stage will be enough.

[goneXC]

I know the feeling well - I literally burnt a Truepath and resurrected it again!

Check out http://www.41hz.com/forums/content.p...ier-Protection for protection circuits. Also, pin 7 on J4 takes an LED for overload indication but whether anyone except you will notice it remains to be seen

[MickB]

Yes it feels good, doesn't it! Thanks for the link, goneXC. I've been looking at input protection diodes and it should be easy to fit a couple of IN4149s which I've got lying around. The AMP11 has several spare input capacitor mounting holes I can use. One diode can go from there to an empty ground connection on J4 and the other across to the 5V leg of Pot1.

Yeah, you're right, the people who need to be looking at the overload LED won't even notice

[MickB]

Input protection diodes fitted...

IMG_3920.jpg

Another thought...

I've used Rin/Rfbk of 22k/47k to give input stage gain of just over 1:2. Presumably the input clamping happens before the input gain is applied, so with a 5V p-p input and 1:2 input gain the output of the amp will be double what it would be with 5V p-p input and 1:1 input gain. Is that correct? So really I ought to work out what the maximum safe input gain should be to avoid overloading the outputs, and then make up any extra gain needed to cater for a weak source by increasing the gain of the preamp instead. Does that make sense? Or am I talking bollocks?

[V-bro]

Nice implementation of the diodes!

But let's not overlook the other 'adjustments' as there may be improvements possible when we tailor the values as best as possible to your supply voltage and source strength. How is the modulator feedback? This consists out of two series connected resistors of which the added values make the total feedback resistance. The values need to match the operating voltage.

[MickB]

Thanks! It's fortunate having some through holes in convenient places.

Supply voltage spends most of the time between 24V and 26V.

It has to be able to cope with a fairly wide range of source strengths. It needs to be able to play loud from a weak mp3 player when necessary. It's also used with the wireless system, the output of which can vary a lot depending on the strength of the source connected to the transmitter, the volume setting of the transmitter itself, and the volume setting of the receiver. The equipment is set up and used by different people so it's not consistent, and if everything is turned up high the input signal from the wireless receiver can be a lot higher than a weak mp3 player.