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LM3886 amp build

malcolm mellersh

Oct 31, 2021
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Having built the amp with all the recommended components I have a growling speaker output and a rd hot positive rail. If I unplug the speaker, the rail cools down. What's the problem?
 

bertus

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Nov 8, 2019
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Hello,

Can you post the used schematic?
That way we can see what is going on.
Is it the one in the attached PDF?

Bertus
 

Attachments

  • LM3886 Audio Power Amplifier Series High-Performance 68W Audio Power Amplifier w-Mute NAT.pdf
    852.4 KB · Views: 5

Audioguru

Sep 24, 2016
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Your circuit has no power supply voltages.
Your schematic does not show the speaker connected to 0VDC.
The output of the amplifier should measure 0VDC.
 

malcolm mellersh

Oct 31, 2021
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Your circuit has no power supply voltages.
Your schematic does not show the speaker connected to 0VDC.
The output of the amplifier should measure 0VDC.
Very true. The power supply is 29VDC negative and 29VDC positive. The input and output are both grounded
 

bertus

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Hello,

Here is the schematic from that page:
CD_Hi-Fi-Audio-Amplifier-With-an-LM3886-Circuit-Schematic.png
Did you connect ALL the ground connections together?
Did you also install Rsn and Csn?

Bertus
 

Audioguru

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The schematic in the video has a signal ground for the input but also has a power ground. It wrongly does not show them connected together.
 

malcolm mellersh

Oct 31, 2021
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Hello,

Here is the schematic from that page:
View attachment 53153
Did you connect ALL the ground connections together?
Did you also install Rsn and Csn?

Bertus
All grounds together. I have checked and signal ground and power ground are radially led to a single point.
I have installed Rsn and Csn
Could I have a faulty Lm3886. If so, how do I check it out?
 

bertus

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Hello,

Wich version of the LM3886 are you using?
There are the LM3886T and the LM3886TF.

Bertus
 

bertus

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Hello,

How large is the heatsink?
The TF version will likely need a larger heatsink, as the case has a plastic cover.

Bertus
 

malcolm mellersh

Oct 31, 2021
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Hello,

How large is the heatsink?
The TF version will likely need a larger heatsink, as the case has a plastic cover.

Bertus
I'm aware of the heat sink. Why is my speaker growling etc.
It's not the circuit and its probably not the components. Its me.
I've made an error somewhere and I can't find it. Can you help?
 

WHONOES

May 20, 2017
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Referring to the schematic as posted by Bertus, if that is what you have built then perfom the following, if not, can you sketch out what you have actually done.

Firstly, disconnect the input ground connection from the ground connection used for the rest of the amplifer and take it direct to the power supply ground.
Secondly, discard D1, Rm and Cm and then connect pin 8 to the amplifier ground.
Thirdly, capacitors Cs1 and Cs2 must be connected as close as is physically possible to the power supply pins of the amplifier.
Lastly, The ground connection for the amplifier needs to be as robust as you can make it.

Try these one at a time so that you will know which one (if any) eradicates your problem
 

malcolm mellersh

Oct 31, 2021
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Thankyou for that.

The signal ground is already directly connected to the power ground. Input socket to input socket.
I have isolated D1, Rm and Cm and connected pin 8 to ground. No difference there, so something else is happening.
I will bestripping back and rebuilding the basic circuit (without frills)
Any further advise would be welcomed.
 

WHONOES

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The signal ground needs to be disconnected from the ground on your board and connected directly to the power supply ground so that it is completely independant from the grounds on the board.
 

malcolm mellersh

Oct 31, 2021
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It is. The signal ground is taken from the signal input socket in the amplifier casing and passed directly to the power input socket in the amplifier casing. It bypasses the board completely.
Power is provided from a separate power supply unit.
 

WHONOES

May 20, 2017
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Can you accurately sketch out what you have actually built and post it on here. Doing so will help us and may even show you where you have gone wrong (if at all).
 
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