Goodbye Mr Chips...
 

Hello to everyone, this is my first post ;)

Unfortunately it brings some sad news....and it was all going so well.....

I got a lovely 4780 kit from Peter Daniel and set about making a small stereo amp as my first ever DIY project.

Having spent the past few days putting the kit together, it was ready for testing today. Well, it worked.....first time. I was well chuffed and then whilst checking the voltages on one of the boards i must have shorted the rails with a probe lead....my stereo has become a mono :mad: ! So frustrating! Guess i'll just have to get hold of another chip....other components look to be ok, so with any luck i can swap the chip out and all will be well.

Whilst I've got all of your attention, I might as well ask...At the moment I have no power switch and sometimes, when plugging in, the 1.6A time delay fuses I'm using blow. Sometimes they don't however...

Using a 300VA Transformer with 25V twin secondaries.

Anyone shed any light on this? Is it just to do with current inrush at power on (i.e. do i need some bigger/longer time delay fuses)? I'm not using any Ci caps or input caps at the mo.

Try a 2A slow blow fuses , and next time be more carefull while you measuring voltages. Use hook-up clips on your intrument probes and fix them on element legs before powering up the amp.

Many thanks for the reply. It was my own silly fault...standard safe procedure went out the window in a flurry of excitement :rolleyes:

Peter Daniel: How much to get a replacement lm4780 from you with shipping to the UK? I'm gonna be stung by big handling fees etc to order in the UK.

If anyone is putting in a Farnell/Digikey order and could help me out here I'd be eternally grateful.

£20 minimum order if I'm not mistaken.....:mad:

Why don´t you buy this chip at local electronic shop , or from Farnell??

LM4780's are on backorder until June. I talked with National a few weeks ago -- they are really ramping production -- but the chips is unobtainium for few weeks more.

Rich, drop me a line, I have a spare! :)

I can send it to you for $10, shipping included. But try pinkmouse offer first.

But on the bright side you have the opportunity to become a Sakuma-san of the chip amps.

You can still wire a single LM4870 chip for a stereo operation ;)

Just separate the inputs, add one more 22k shunt resistor and pick up both outputs before 0.1 R resistors (lifting their other ends from the board). You might even like it more than a parallel version ;)