Wow, this is awesome! Thank you! It worked!
I have a bunch of old caps of various types laying around so I put a 1uf electrolytic cap across the mute pin and didn't notice a difference, but a 10uf cap actually made the thump go away! There was still a brief hiss sound after a short delay so I tried a 22uf cap and that made the hiss go away as well. I'd say 10uf in a pinch will do it, but 22uf (or maybe higher on some) will get rid of more of the startup noise. There is still a tiny "tick" sound from the speakers as soon as I throw the switch, but I doubt it is hurting anything. I tried adding a 1uf and then a 10uf cap across the STBY cap and it didn't seem to get rid of the tick sound. It is probably just a side effect of this being an $8.50 amp+case+power supply bundle.
Thank you so much! This will take me maybe a minute to solder a cap right on there, and I can easily do it to both of them.
This is by far the simplest solution I could have imagined to fix these things. I've been blaring some music on them using a couple of KLH 911B bookshelf speakers I picked up for $10 last week and it sounds quite decent. Sure beats $18.50 worth of computer speakers.
If I can possibly retain some of this information I think I will have learned some valuable lessons about circuits as well. This site is great.
By the way, I will probably post this over at the PE Techtalk forum since I would expect many many people who bought these over the past month or two to go looking for a solution to this.
EDIT: It took maybe 30 seconds to fix this once I had the soldering iron out. A picture of the repair is attached.
I've added the picture to the gallery as well.
FX Audio 7492P Mini Amp - Google Photos
I have a bunch of old caps of various types laying around so I put a 1uf electrolytic cap across the mute pin and didn't notice a difference, but a 10uf cap actually made the thump go away! There was still a brief hiss sound after a short delay so I tried a 22uf cap and that made the hiss go away as well. I'd say 10uf in a pinch will do it, but 22uf (or maybe higher on some) will get rid of more of the startup noise. There is still a tiny "tick" sound from the speakers as soon as I throw the switch, but I doubt it is hurting anything. I tried adding a 1uf and then a 10uf cap across the STBY cap and it didn't seem to get rid of the tick sound. It is probably just a side effect of this being an $8.50 amp+case+power supply bundle.
Thank you so much! This will take me maybe a minute to solder a cap right on there, and I can easily do it to both of them.
This is by far the simplest solution I could have imagined to fix these things. I've been blaring some music on them using a couple of KLH 911B bookshelf speakers I picked up for $10 last week and it sounds quite decent. Sure beats $18.50 worth of computer speakers.
If I can possibly retain some of this information I think I will have learned some valuable lessons about circuits as well. This site is great.
By the way, I will probably post this over at the PE Techtalk forum since I would expect many many people who bought these over the past month or two to go looking for a solution to this.
EDIT: It took maybe 30 seconds to fix this once I had the soldering iron out. A picture of the repair is attached.
I've added the picture to the gallery as well.
FX Audio 7492P Mini Amp - Google Photos
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Small update!
The "tick" was bugging me because the rest sounded so good, so I tried a 22uf on the STBY cap (C3) and a 33uf on the MUTE cap (C4)... and now there is almost no sound when the amp turns on! It nicely fades the audio in if there is already something playing. It is a tasteful amount of delay, not obnoxiously long, and it gets rid of the "cheapness" sound of an amp that wants to ruin your speakers every time you switch it on (though we'll see what high volume listening does).
The "tick" was bugging me because the rest sounded so good, so I tried a 22uf on the STBY cap (C3) and a 33uf on the MUTE cap (C4)... and now there is almost no sound when the amp turns on! It nicely fades the audio in if there is already something playing. It is a tasteful amount of delay, not obnoxiously long, and it gets rid of the "cheapness" sound of an amp that wants to ruin your speakers every time you switch it on (though we'll see what high volume listening does).
You're welcome.
If I can possibly retain some of this information I think I will have learned some valuable lessons about circuits as well. This site is great.
Small hint ... don't try to memorize it, try to understand it
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