This is a teardown of the Monoprice 150 watt Class D Amplifier which I just reviewed. The owner gave me kind permission to open it up.
Here is the overview shot of the entire unit:
The heart of the unit is an integrated switching power supply and stereo class D amplification.
I was surprised to see an angled bottom mounted fan in a rack mounted device! Usually there is equipment stacked on top of each other, not leaving any air in there to suck in. Granted, this fan is tilted a bit but still. Even if intake air is available, it is just blown randomly against the top of the case. It will surely provide more cooling than without but most certainly not optimized. Good news is that it is a larger fan so you can get quiet versions or even temperature controlled ones. It is nicely socketed as marked so replacement should be easy.
That monster shrink wrapped bit must be some kind of choke/filter. Alas, it has already pulled apart the cheesy glued cable tie:
All such fasteners should be screwed to the case, not glued. Even if it had not come loose now, it would have in the future.
Moving on, I noticed a serious safety issue:
These are the mains wiring and the one blue wire is in touch with the sharp edge of the fan shroud. The vibrations from the fan will cause the edge to act like a knife, potentially cutting through the insulation. Once there, it is shorting that wire to the chassis. If it is a neutral wire you will still be safe but may get ground loops and hum. If it is the hot lead, it may spark and potentially cause a fire. The whole harness needs to be heck away from that edge using a fastener on the side or something.
Let's now zoom into the amp/power supply board:
Other than over zealous goop put everywhere including partially covering a power transistor, the rest seems to be OK.
Class D amplification comes courtesy of IR/Infeneon, IRS2092:https://www.infineon.com/dgdl/irs2092.pdf?fileId=5546d462533600a401535675f1be2790
The IC is only a controller though and requires output mosfets for power delivery:
The MOSFET used is IRFB4020 which is a specialized part designed for output stage of a class D amp with a power rating of 300 watts: https://www.infineon.com/dgdl/irfb4020pbf.pdf?fileId=5546d462533600a4015356158ffd1e05
Looking at the weak point of switching power supplies which tends to be the capacitor, we find a no-name Junzl brand:
Fortunately it is rated at 105 degree C so won't degrade quickly.
I could not find any useful marking on the boards to identify who designed them.
Conclusions
There is certainly a lot to this amplifier despite its extremely low price. The one safety issue is ready to remedy by moving the mains power away from the fan enclosure. Speaking of fan, its noise can easily be remedied by disconnecting it, making it temperature sensitive or putting in a quieter fan. If you do leave it in there, be sure there is circulation on the bottom and side of the unit.
Overall, not a bad showing especially for this price.
------------
As always, questions, comments, recommendations, etc. are welcome.
After having some nice take out Fish and Chips at our local waterfront seafood restaurant (consumed in our car
), the night's project was to dehydrate these Asian Pears from our orchard:
Well... that was easier said than done. These have extremely hard cores and I managed to jab my hand with the tool I use to take them out. It drew a bit of blood but the good news is that the dehydrator is full and running overnight. I think we have another 200 or more pears to go and no way I am going through this process with them again! So we will likely donate most of them to the local food bank.
As I noted, if you want these boring garden stories to go away, you need to donate money using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
Here is the overview shot of the entire unit:
The heart of the unit is an integrated switching power supply and stereo class D amplification.
I was surprised to see an angled bottom mounted fan in a rack mounted device! Usually there is equipment stacked on top of each other, not leaving any air in there to suck in. Granted, this fan is tilted a bit but still. Even if intake air is available, it is just blown randomly against the top of the case. It will surely provide more cooling than without but most certainly not optimized. Good news is that it is a larger fan so you can get quiet versions or even temperature controlled ones. It is nicely socketed as marked so replacement should be easy.
That monster shrink wrapped bit must be some kind of choke/filter. Alas, it has already pulled apart the cheesy glued cable tie:
All such fasteners should be screwed to the case, not glued. Even if it had not come loose now, it would have in the future.
Moving on, I noticed a serious safety issue:
These are the mains wiring and the one blue wire is in touch with the sharp edge of the fan shroud. The vibrations from the fan will cause the edge to act like a knife, potentially cutting through the insulation. Once there, it is shorting that wire to the chassis. If it is a neutral wire you will still be safe but may get ground loops and hum. If it is the hot lead, it may spark and potentially cause a fire. The whole harness needs to be heck away from that edge using a fastener on the side or something.
Let's now zoom into the amp/power supply board:
Other than over zealous goop put everywhere including partially covering a power transistor, the rest seems to be OK.
Class D amplification comes courtesy of IR/Infeneon, IRS2092:https://www.infineon.com/dgdl/irs2092.pdf?fileId=5546d462533600a401535675f1be2790
The IC is only a controller though and requires output mosfets for power delivery:
The MOSFET used is IRFB4020 which is a specialized part designed for output stage of a class D amp with a power rating of 300 watts: https://www.infineon.com/dgdl/irfb4020pbf.pdf?fileId=5546d462533600a4015356158ffd1e05
Looking at the weak point of switching power supplies which tends to be the capacitor, we find a no-name Junzl brand:
Fortunately it is rated at 105 degree C so won't degrade quickly.
I could not find any useful marking on the boards to identify who designed them.
Conclusions
There is certainly a lot to this amplifier despite its extremely low price. The one safety issue is ready to remedy by moving the mains power away from the fan enclosure. Speaking of fan, its noise can easily be remedied by disconnecting it, making it temperature sensitive or putting in a quieter fan. If you do leave it in there, be sure there is circulation on the bottom and side of the unit.
Overall, not a bad showing especially for this price.
------------
As always, questions, comments, recommendations, etc. are welcome.
After having some nice take out Fish and Chips at our local waterfront seafood restaurant (consumed in our car
), the night's project was to dehydrate these Asian Pears from our orchard:Well... that was easier said than done. These have extremely hard cores and I managed to jab my hand with the tool I use to take them out. It drew a bit of blood but the good news is that the dehydrator is full and running overnight. I think we have another 200 or more pears to go and no way I am going through this process with them again! So we will likely donate most of them to the local food bank.
As I noted, if you want these boring garden stories to go away, you need to donate money using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
