Amp Camp Amp - ACA


2022-04-11 10:57 pm
I will add, that I know it is exciting to try and get your project working, but I would kindly suggest you watch a few soldering videos, and if possible find a practice board to work on.

As others have mentioned, a lot of it revolves around your soldering iron (tip size and wattage mainly) and type of solder you are using, the cleanliness of leads and board (before soldering) and use of flux. The flux is usually provided from flux core solders, but you can also buy liquid flux to help.

Also properly cleaning and tinning of your soldering tip is important. If you don't already have one get one of those Brillo pad type of tip cleaners and use it every time you solder a joint.
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This is my first amplifier build so excuse the questions but I just finished putting it together this afternoon. I plugged it in and saw some smoke. I tried a few things but kept seeing smoke coming from mosfet Q2. After a while, the LEDs started flashing on and off. I read elsewhere that the power supply goes into protection mode when there is a short and oscillates between 24v and 5v. I then found a short on one of the boards and I think one or both of the IRFP240 mosfets are now dead.

Not sure what the best plan of action is. I guess I should order some more of those mosfets and hopefully that will resolve the issue, are any other components likely to have been damaged?

Any suggestions are welcome.

I've attached some pictures of that board.


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Thanks, just did that and mostly seem to be alright especially around Q1 and Q2. I just checked the keratherm insulation and here are two pictures of the one under Q2. Do you think that tear could be enough to have created a short?


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The metal tab on Q2 is connected directly to the Drain. If it was shorted to the heatsink then it would short out the 24volt line and give the pulsing symptom you describe.
That is a strange tear and you need to replace it. Is the black ring from Q2 or a burn mark? Any stray solder blobs or loose strands cause shorts, be meticulous on re-assembly. Check with your meter that it is not shorted too.
Okay, I'll take my time on re-assembly and I believe the black ring is a burn mark. I'm based in the UK and I can't find anyone with 86/82 with precut holes in stock but I did find this

which I could use to cut suitably sized pads. I gather the mounting hole needs to be precise, do you have any good suggestions for making the hole as precise as possible?
Pa did found sweet spot, how lower ( more active, governor) and upper (follower) mosfets are cooperating

feel free to alter voltage level of output node and inform us

Thanks for the article, very enlightening. When I first set up my ACA I set the bias at around 10v not realising that for 24v it should have been around 12v. It could be anticipation bias, but I think it sounded sweeter at that voltage. I just wondered if going too far in any direction say 8v or 14v would do any damage.