This last month I have been trying to build an amplifier using LM3886 chip.
This is my first try in the complementry supply. Till now I have been "playing" with single supply chip like TDA7375.
Well I have used the circuit and component values National suggest at the first page of it's datasheet. You can see the circuit board I made (red lines are short wirrings, blue capacitors and green resistors.)
Well here is the real problem.
I put everything on that board including the heat sink and then supply it.
what I get? +40 volt at the output...
with no input signal.
The supply I use is +, - 41.8Volt.
Ok there was a miss calculation somewhere there and got a 2x30Volt 150Watt toroidal for my 2x50Watt amplifier.
(Wana be amplifier).
But I imagine, if that was the problem there would be no output at all (power protection) and not +40Volt.
Ok I know it is a bit high (at the limit of the chip). When the supply is open air I measure +41.8 and -41.8 but then when I connect it to the board and measure the supply voltage at pin 1, 5, 4 it is +38V and -38V
It is strange to me that I hear everyone say how good that chip "work" and all I get is +supply at the output (pin #3), having nothing connected as input signal. Thank god I measured the output before I connect it to the speaker, or I would have them in my hand
I also get that +40 volt at the output, even if the mute pin has no curect drown from it.
Is it realy that power supply I use? or something else?
Then I think, I might have used a wrong feedback resistor and the amplifier work as a comparator, but checking them I find that the values I used are the correct.
Hope for a reply and even better a solution
Thanks for your time
Tasos.
This is my first try in the complementry supply. Till now I have been "playing" with single supply chip like TDA7375.
Well I have used the circuit and component values National suggest at the first page of it's datasheet. You can see the circuit board I made (red lines are short wirrings, blue capacitors and green resistors.)
Well here is the real problem.
I put everything on that board including the heat sink and then supply it.
what I get? +40 volt at the output...
with no input signal.
The supply I use is +, - 41.8Volt.
Ok there was a miss calculation somewhere there and got a 2x30Volt 150Watt toroidal for my 2x50Watt amplifier.
(Wana be amplifier).
But I imagine, if that was the problem there would be no output at all (power protection) and not +40Volt.
Ok I know it is a bit high (at the limit of the chip). When the supply is open air I measure +41.8 and -41.8 but then when I connect it to the board and measure the supply voltage at pin 1, 5, 4 it is +38V and -38V
It is strange to me that I hear everyone say how good that chip "work" and all I get is +supply at the output (pin #3), having nothing connected as input signal. Thank god I measured the output before I connect it to the speaker, or I would have them in my hand
I also get that +40 volt at the output, even if the mute pin has no curect drown from it.
Is it realy that power supply I use? or something else?
Then I think, I might have used a wrong feedback resistor and the amplifier work as a comparator, but checking them I find that the values I used are the correct.
Hope for a reply and even better a solution
Thanks for your time
Tasos.