first atemp to make a gc gone wrong

[wuffer]

thanks... out to the shop im going

 

[wuffer]

dosent work here.. the speaker membrane just go in and stays there untill its dead...

i have dobbel tjeck it and cant seem to find anything wrong

maybe its ment to be that i should not have i gc

 

[Nuuk]

dosent work here.. the speaker membrane just go in and stays there untill its dead...

Did you measure the DC offset before you connected the speakers?

 

[wuffer]

nopz.. im not sure how...

luckly i have some small speakers to test with


hmm that is just wrong.. i got full voltage to the speaker

 

[boholm]

Without anything connected, what are the voltages of input and output?

With input grounded what is the voltage of output?

 

[wuffer]

0,3 on the input and 34,5 on the output without anything connected

voltage is the same with and without the ground

 

[Nuuk]

OK, you should ahve the same voltage on the positive and negative rail!

So you have a problem in the PSU somewhere.

I just completed a new GC this morning. I tested the voltage from the rectifiers before I connected up the regulators, then I tested the input voltages on the regulator and the output voltages. Only when I saw that they were correct did I connect the chips and even though this is a GC that I have used before, I still checked the DC offset! And even though the offset readings were 19mV and 20mV, I still connected my old test speaker and played music through each channel before connecting my 'good' speakers.

Testing for DC offset is described on Decibel Dungeon so it's 'back to school' for you Mr Wuffer!

 

[wuffer]

the psu is just like this one..

An externally hosted image should be here but it was not working when we last tested it.

but i will read som more...

 

[Nuuk]

the psu is just like this one..

And do you have +35 volts on one side and -35 volts on the other?

And have you connected one negative rail to the positive rail on the other 'side'?

When you measure the voltage on your chips, you should measure between the voltage pin (positive or minus) and the power ground star which is at 9or should be at) zero volts.

Have you connected pin 5 to the positive suply?

 

[wuffer]

1. yes i got that

2+3 im not sure i understand that.. my brain is on weekend

4. yes

 

[Nuuk]

2+3 im not sure i understand that.. my brain is on weekend

Is you power supply connected exactly as it is shown in the diagram?

If so you should have three (not four) wires coming from it - positive voltage, negative voltage and zero volts.

 

[wuffer]

yes 3 wires..

 

[Nuuk]

yes 3 wires..

So, when we say measure the voltages on the pins, we mean that you should measure between the positive wire (where it joins the chip) and the zero volt wire (where it joins the power ground star. And likewise for the negative rail.

 

[wuffer]

+35 and - 35 volt..

just stop for today...

 

[Nuuk]

just stop for today...

That's very wise! When having problems, a break can make all the difference in spotting what is wrong!

 

[wuffer]

looked at it again.. cant seem to find any errors... looking at it again tomorrow.. there must be an error

 

[Nuuk]

looked at it again.. cant seem to find any errors..

I think we have all thought that we have checked everything, only to find something wrong later. Sleep on it and don't worry.

 

[wuffer]

i just looked at it again... the -v is connected on pin 3 but in http://cache.national.com/ds/LM/LM3886.pdf it should be on 4.. and on yor website Nuuk its connected under the 1000 caps and on the other diagram its pin 3... im confused..

 

[jaudio]

For the lm3886 chip pin 3 is output and pin4 is -v.

 

[Nuuk]

My apologies Wuffer. I had got it wrong and have now corrected those diagrams.

I hope that this is the only 'problem' and that you will now have a working GC!