LA4440 amplifier circuit - Page 1
Forum section: electronics / beginners

author: Adhith
author_rank: Frequent Contributor
timestamp: October 10, 2016, 05:01:15 pm
content: hello everyone..just made a 6w stereo amplifier circuit with LA4440 ic. but as soon as i switch on the circuit all i could here is a loud hissing sound. the supply is 12v (1A) regulated voltage. what may be the reason ?? the circuit that i have used is attached below.

author: Zero999
author_rank: Super Contributor
timestamp: October 10, 2016, 05:28:12 pm
content: how is the circuit assembled?Did you use the layout recommended by the data sheet?http://www.onsemi.com/pub_link/Collateral/EN750-D.PDF

author: Adhith
author_rank: Frequent Contributor
timestamp: October 10, 2016, 05:47:51 pm
content: Quote from: Hero999 on October 10, 2016, 05:28:12 pmi assembled it on a breadboard. yes i have followed the layout.7812 ic coupled with a 100mf cap was used to drive a regulated voltage of 12v. the amp(la4440) is slightly heating , this shows that its working right??on the input instead of 22k i used 44k dual potentionmeter. but the loud noise persist before plugging the aux cable. is it any problem with the grounding??IT IS SEEN THAT THE DMM SHOWS ABOUT 5.5V FROM THE SPEAKER OUTPUT WIRES WHEN NO AUDIO INPUT IS GIVEN..

author: Zero999
author_rank: Super Contributor
timestamp: October 10, 2016, 06:07:35 pm
content: If you're absolutely sure all the connections are right and the IC is genuine (not a fake) then it's highly likely that it's a layout problem. The IC is not designed to be assembled on a breadboard with the poor connections and long leads which add parasitic inductance and capacitance to the circuit at different points.Ideally it needs to be assembled on a PCB with a similar design to that suggested on the datasheet. If it's not convenient for you to get a PCB etched then you could try using strip board but don't expect brilliant performance.

author: Adhith
author_rank: Frequent Contributor
timestamp: October 10, 2016, 06:20:02 pm
content: Will there be always a voltage supply from ic to speaker when no audio input is given ?? (I got 5.5v from DMM)Is this voltage causing the problem? The layout is taken from a website. In the datasheet there is a modification in the same circuit. It includes a additinal 1000mf cap coupled to the input power supply & to the speakers will it make any difference ??

author: ciccio
author_rank: Frequent Contributor
timestamp: October 10, 2016, 06:28:21 pm
content: Quote from: Adhith on October 10, 2016, 05:47:51 pmThere is obviously a voltage (about half the supply voltage) on IC putput pins (pin 10 and pin 12).This is the reason for the output capacitors. But there cannot be a voltage on the speakers, if these are wired correctly and the output caps are present and with the correct polarity.It is possible that the amp was damaged at switch-on if the output capacitors are not installed or reverse biased.Best regards.

author: Zero999
author_rank: Super Contributor
timestamp: October 10, 2016, 06:32:01 pm
content: Quote from: Adhith on October 10, 2016, 06:20:02 pmApart from a tiny amount of noise, there should be no voltage on the speaker, when nothing is connected to the input.Sorry, I didn't compare the schematic you posted with the one on the data sheet, when I posted last. It's wrong. The output capacitors are too low and the Zobel network is incorrect. Please save yourself the trouble and use the circuit at the top of page three on the data sheet linked below:http://www.onsemi.com/pub_link/Collateral/EN750-D.PDF

author: Adhith
author_rank: Frequent Contributor
timestamp: October 11, 2016, 02:53:42 am
content: thank you my friends..let me try the pcb to see what happens.. & let you guys know about it

author: Adhith
author_rank: Frequent Contributor
timestamp: October 12, 2016, 09:58:00 am
content: I have made the amp & it works fine..apart from low bass response, I'm thinking of a bass boost circuit which can be coupled with the amp for a better audio performance. can anyone suggest any ideas??

author: Zero999
author_rank: Super Contributor
timestamp: October 12, 2016, 10:05:55 am
content: Quote from: Adhith on October 12, 2016, 09:58:00 amWhat values are you using for AC coupling capacitors (the ones in series with the speakers)? If it's only 220µF then that's not surprising, increase them to 1000µF.Failing that, it could be your speakers are too small to have good bass response or are not in a properly designed enclosure, which is important for good bass response.

author: Audioguru
author_rank: Super Contributor
timestamp: October 12, 2016, 03:27:41 pm
content: The Electro-whatever website makes many errors. The datasheet shows the important missing parts.The voltage gain is very high at almost 400 times (!) so output hiss noise will probably be audible. Negative feedback resistors can be added to reduce the gain at the risk of oscillation.With 220uF output capacitors feeding 4 ohm speakers then 182Hz (upper bass) will be at half power and lower frequencies will be reduced a lot more. Bass boost does not boost the low frequencies, instead it reduces mid and high frequencies.A solderless breadboard guarantees that the circuit will oscillate at a high frequency. Use a pcb instead.