Goodbye Mr Chips...

[richgraham]

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 ! 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.

[Gasho]

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.

[richgraham]

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

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.

[richgraham]

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

[Gasho]

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

[jackinnj]

Originally posted by Gasho
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.

[pinkmouse]

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

[Peter Daniel]

Originally posted by richgraham
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.

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

[analog_sa]

my stereo has become a mono ! So frustrating!

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

[Peter Daniel]

my stereo has become a mono ! So frustrating!

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