LM3886 very hot

[ivan-UTN-ARG]

first of all...my english is bad...

I built an stereo amp with 2 x LM3886.

The sulppy is +/-36V with max load...

the amplifier wokrs fine... sounds very well... BUT...

it's very very hot... with no singal and with max singal !!!!

the heatsink is big enough...about 400 cm2

i need help....

[ivan-UTN-ARG]

I'm using 8 ohms loads...

the supply is about +/-36V with load

the heatsink is big enough ( i think) ... about 400 cm2

i have 1.9 V of dc in both channels .... WHY???????

here i post some photos of my amp...

i forgot to put the mute resistor an cap in the schematic ... they

are conectet under the board

[ivan-UTN-ARG]

this is the schematic

[ivan-UTN-ARG]

this is the PCB ... in forgot to put the mute resistor and cap on the PCB

[ivan-UTN-ARG]

and this is the complete amp under test ... i have a lot of things

to finish ...

and...thanks for everybody....

the photos are small... i heve some problems with internet....

[CJ900RR]

If it is the amp in your previous post then lower the voltage. That heatsink is not good enough to keep the temp down. Also, you are using the isolated version of LM3886, TF. I think it require a lower voltage to work properly.

[markiemrboo]

Originally posted by ivan-UTN-ARG

i have 1.9 V of dc in both channels .... WHY???????

Oscillation? Do you have an oscilloscope you can check with? If not, try putting a light bulb, about 100W, in series with the mains live between the mains input and the transformer mains wires. It should flash bright very briefly and then, when playing no music, fade out to not lit up at all or only lit up very dimly. If it stays lit up brightly this may be an indication that it is oscillating.

Do you have 100nF power supply bypass capacitors (from the +ve rail to ground and the negative rail to ground) close to the chip pins? I don't see them in the pictures.

[TroelsM]

If the bolt in the toroid is in electrical contact with the chassis you have a potential bad situation as there might be a short-circuit of the toroid. You should use another point as your GND. Do never use the toroid-bolt. It's very bad practice.

This would draw a lot of current from the mains, but it shouldn't result in DC on the outputs.

Regards TroelsM

[carlmart]

Originally posted by ivan-UTN-ARG
I built an stereo amp with 2 x LM3886.

The sulppy is +/-36V with max load...

the amplifier wokrs fine... sounds very well... BUT...

it's very very hot... with no singal and with max singal !!!!

the heatsink is big enough...about 400 cm2

Supply is a bit high, but that shouldn't be any problem, as long as you don't load this amp with 4 ohm speakers. What speakers are you using?

The heatsink is too small and the wrong shape. Use more ribs, vertical, in a larger heatsink. Black if possible. The "hand temperature test" works every time: you should be able to leave your hand on the heatsink for a minute or so.

If it's not oscillating (do lamp test as explained by markiemrboo), then the problem is just a question of dissipation. But it's strange, because this chip doesn't get too hot.

[carlmart]

Originally posted by ivan-UTN-ARG
this is the PCB ... in forgot to put the mute resistor and cap on the PCB

Where is the mute resistor then?