Big thud on startup ACA and after 5 minutes one channel stops

[mickeyg007]

Hello everyone,

I have finished my second ACA and this one has 2 problems. First one works great.
1) big thud in right channel on power up and. Both channels after thud emit the usual whining sound.
2) left channel goes silent after 5 minutes or so.

I checked all connections/soldering/continuity etc.

The amp runs slightly warm not hot like normally does.

Could it be the voltage is too high, spike (I use a voltage reg) although I took good care to keep it at or very near 12v

Any other suggestions?

Thanks

 

[rayma]

First, do not connect this amp to your speakers until the problem is resolved.
It is likely to do damage otherwise.

Check all DC voltages, and compare the good and bad channels.

 

[TonyTecson]

ACA is cap coupled to speakers so i will not be too concerned, look for loose solders, i suspect that is your issue, i built over 50 pairs of these years back and it worked the first time, only need adjustment of voltage, and after that it is all go..
sure, we encountered wrong components insertions, but that was not fatal, very easy to correct..

 

[avtech]

Any pics of your boards?

 

[Eric]

After checking the PCB for inadvertent solder bridges (physically scratch between ALL solder pads with a flat blade micro screwdriver to be sure) and incomplete solder joints (inspect with a bright light and a magnifier glass), make sure that none of the PCB components are shorting to the heat sink. The 5min delay might be enough time for something to heat up and expand, thus causing your problem. Another problem to check for is your Mosfet mounting. If you tapped your own holes and used soft sil-pads for insulation, make sure that there are no little aluminum slivers piercing the pads. This is why I no longer use silpads: easy to pierce with nearly invisible threads of aluminum from tapping holes.

 

[TonyTecson]

Any pics of your boards?

 

[mickeyg007]

Thanks everyone.
There was in fact a loose ground on the PCB which, after a "little dab'll do you" soldering it solved my problem. - Partially:

Now the same channel will cut out at some point. I give it the old time proven solution of a little tap and it solves the problem. Will check thouroughly for any loose connection/weak soldering points.

For the last question, I have 3 ACAs and the one I am talking about runs only warm in comparison to the other 2. Any ideas?

Thanks so much

 

[Eric]

I’ll bet that once you fix your soldering issues, your temps will be well behaved. If a tap on the chassis makes something work or not work, it sounds like you need to do some more inspection and reflowing of your solder joints. Start with a bright light and inspect every joint with a magnifier. Every solder pad should be fully covered with no gaps, solder should be smooth and even, forming nice slopes between device legs and the solder pads. Anything less needs to be reflowed.

 

[mickeyg007]

Thanks Eric.

Weekend project. Good thing it's only on 1 PCB....