How to find a mistake. Sound amplifier circuit board. Need help with troubleshooting

Thread Starter

Pashgen

Joined Nov 16, 2017
23
Hi,

I bought DIY amplifier board.
And now I am trying to find what I did wrong. It can work for about 2 seconds and then sound dissappear.
But power stays on, and LED is glowing

I connected 24 volt toroid to start the board. In description it says that circuit is designed for 12 to 36 AC voltage. I checked tor, and it's all good, there is 24 volt AC.
I guess I should start looking at power first. Such as diode bridge. I got multimeter to troubleshoot. But I don't want to power up amplifier until I hear opinion of more experienced people.
Please help me to find mistakes. I am learning.
 

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bwilliams60

Joined Nov 18, 2012
1,398
Can you take some really good clean pics of the soldered side of the board and post them up. Also the capacitor in the 4th picture labelled 10U it looks like, is the top of it domed or is that just the camera angle.
lastly, it may help you if you draw out a schematic for your project so that you and others can follow along in your diagnosis. Surprised it didn't come with one. Perhaps the manufacturer has one?
 

anniel747

Joined Oct 18, 2020
1,040
Hi,

I bought DIY amplifier board.
And now I am trying to find what I did wrong. It can work for about 2 seconds and then sound dissappear.
But power stays on, and LED is glowing

I connected 24 volt toroid to start the board. In description it says that circuit is designed for 12 to 36 AC voltage. I checked tor, and it's all good, there is 24 volt AC.
I guess I should start looking at power first. Such as diode bridge. I got multimeter to troubleshoot. But I don't want to power up amplifier until I hear opinion of more experienced people.
Please help me to find mistakes. I am learning.
No heatsink(s)?
 

LesJones

Joined Jan 8, 2017
3,172
Tracing the power input circuit it looks like it is designed to work with a transformer with a center tapped secondary. You only seem to have two wires connected between the transformer and the board. The DC common rail will float to some unknown voltage with respect to the main positive and negative rails.

Les.
 

anniel747

Joined Oct 18, 2020
1,040
Tracing the power input circuit it looks like it is designed to work with a transformer with a center tapped secondary. You only seem to have two wires connected between the transformer and the board. The DC common rail will float to some unknown voltage with respect to the main positive and negative rails.

Les.
Problem solved.
 

Thread Starter

Pashgen

Joined Nov 16, 2017
23
Tracing the power input circuit it looks like it is designed to work with a transformer with a center tapped secondary. You only seem to have two wires connected between the transformer and the board. The DC common rail will float to some unknown voltage with respect to the main positive and negative rails.

Les.
Yes! It worked! Thank you so much!
 

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Audioguru again

Joined Oct 21, 2019
3,173
The LM3886 amplifiers are smart, read about it in their datasheet. If they detect over-heating then they shutdown (mute). They do not burn up. The amplifiers are class-AB and the datasheet shows that with 12W into 8 ohms, the heating is 14W.

The photos show a stereo amplifier but the printed circuit board is for a mono amplifier.

With your 24V center-tapped transformer, the output power into 8 ohm speakers at low distortion is only 12W per channel.
 

anniel747

Joined Oct 18, 2020
1,040
The LM3886 amplifiers are smart, read about it in their datasheet. If they detect over-heating then they shutdown (mute). They do not burn up. The amplifiers are class-AB and the datasheet shows that with 12W into 8 ohms, the heating is 14W.

The photos show a stereo amplifier but the printed circuit board is for a mono amplifier.

With your 24V center-tapped transformer, the output power into 8 ohm speakers at low distortion is only 12W per channel.
Are you saying those cannot malfunction?
 

Thread Starter

Pashgen

Joined Nov 16, 2017
23
The LM3886 amplifiers are smart, read about it in their datasheet. If they detect over-heating then they shutdown (mute). They do not burn up. The amplifiers are class-AB and the datasheet shows that with 12W into 8 ohms, the heating is 14W.

The photos show a stereo amplifier but the printed circuit board is for a mono amplifier.

With your 24V center-tapped transformer, the output power into 8 ohm speakers at low distortion is only 12W per channel.
Just finished it. Here is pics:

I found old 24v fan. I think it's OK to connected like that. Seems fine.
And I used old cpu heat sink. Applied Thermal paste. Testing it now. Sounds awesome! Everything cold!
Thank you for your help :)
 

Attachments

LesJones

Joined Jan 8, 2017
3,172
The heatsink would be better rotated by 90 degrees so the fins are vertical. With just convection cooling the airflow would be between the fins and the same with the way the fan is mounted. An alternative would be to move the fan to the end of the heatsink so the airflow was between the fins.

Les.
 
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