Has anyone ever used the LA4440 amp chip!?

[Renegadrian]

I got that LA4440 chip for cheap, made a small layout using a schem I found on the net (unfortunately there's not much info on that chip...)


managed to put that in a 1590A.
it works so good on the first quarter of the pot rotation, after that the sound gets distorted and horrible.
tried also to put a 100n cap and 4.7r res to ground on the speaker outs, as other schems have, but didn't make so much difference. going guitar straight or with preamp/pedal/multifx gives the same result. tried a 4ohm and a 16ohm speaker, same result.

Anyone knows how to get an usable amp on higher volumes?!

[Gus]

http://www.onsemi.com/pub_link/Collateral/EN750-D.PDF

Note polyester is specified at C5 and C6 page 3 and 4.  I would use the RC's

It has thermal protection. How big is the heatsink you are using? Iit might be cutting out because of thermal protection.

What is you power supply rated for voltage and current?  If not enough current you will get distortion.

http://pdf1.alldatasheet.com/datasheet-pdf/view/40088/SANYO/LA4440.html
http://www.instructables.com/id/LM4440LA4440-12W-AUDIO-AMPLIFIER-WITH-12V/

[Renegadrian]

the chip lies flat on the inside of the enclosure, so the whole box acts as heatsink (it gets slightly warm)
power supply is a 12V 3A (plenty of current here.)

[Gus]

if a 1590 I would guess you have a bad thermal transfer to the box and too small an area heat sink http://www.hammondmfg.com/pdf/1590B.pdf
You need a very flat surface even using thermal compound.

Warm does not mean much it could be thermal protection turning it on and off reducing the heat.

I would machine the 1590 surface flat trying for a near mirror finish

[PRR]

At 13.2 Volts supply, 4 Ohm Bridge load, it will need 1.5 Amps of supply current.

At 12 Volts supply, 4 Ohm Bridge load, it will need 1.4 Amps of supply current.

At 9 Volts supply, 4 Ohm Bridge load, it will need 1.1 Amps of supply current.

It is entirely easy to have 10 Watts of heat in the chip.

The naked chip can throw 4 Watts. (This may relate to your build being OK at low output but cuts-out at high output.)

The chart on page 2 suggests 100mm by 100mm (4" square) 1.5mm (1/16") thick sink for 10 Watts on a hot stage.

The bottom of a 1590A is barely that big and thick.

And it says it is Aluminum (but maybe cut with Zinc?)

Note that if the box lies chip-down on a surface, the most critical part of the surface area is against the floor, not cooling at all.

As Gus says, the LEAST un-flatness between chip and sink will ruin heat conduction. Die-cast boxes are not sure to be very-flat.

In the intended use for car-radio chips like LA4440, heat sinks are carefully bent sheet-metal (flat by rolling) or purpose-made aluminum castings with mounting surface flatness carefully controlled.

[Hatredman]

10W dissipation means roughly 7W if the device is a Class B amplifier.

Maybe 2,5W is enough for a stompbox-sized power amplifier (considering barechip 4W dissipation)?

If you want more, a Hammond stompbox maybe is not the apropriate enclosure...


My two BRL cents (on today's exchange rate, USD 0,005 - half a penny).