This is a miniature Class D power amp. It is comprised of a modded TPA3118 board from amazon, and an AMZ mosfet booster circuit.
Powered with an old laptop charger (19.5V, 3.5A), it is quite loud and sounds pretty clean. There have been many threads on this forum about others' builds, so I may be rehashing some comments.
Key Build Points:
-Removed the resistor on the TPA board from pin7 to pin8. (it was 100k on mine). The resistor from pin8 to GND is 39k, so according to TPA3118 datasheet page 14, the gain is set to 32dB. Online forums say that this internal gain is responsible for the HISS. Removing the 100k puts the gain at 20dB, and the hiss is gone.
-AMZ Mosfet booster in front to recover the gain lost from the resistor removal. I expected the Hiss may return when signal is boosted, but it did not. So, the hiss was being generated within the TPA at the higher gain.
-The AMZ booster is powered by the input power, through a L7809 (TO-220 package), with 100n to Gnd on the input and output. I lightly epoxy glued it to the side of the enclosure. The tab is touching, but not screwed to the enslosure, so the heat transfer is not probably not great, but the AMZ doesn't draw much current anyway.
-50kA volume pot between the booster circuit and the TPA board
-Output spearker jack must be isolated type. No sleeve to enclosure connection.
Here's my long project timeline:
-March 2021 - inspired by pedalpcb listing the TPA board, but it was out of stock, I purchased a fake TPA3118 board from amazon. Lots of hiss, and not actually that impressive loudness with various power supplies. Tried some buffers and boosts but never sounded good. I housed it in the white enclosure, but never used it.
-April 2026 - read about the existence of fakes and confirmed mine was the fake 28pin. Purchased another board from amazon, confirming in comments it's 32pin. Volume was stronger, but still loud hiss sound making it unusable to me.
-August 2026 - working on a solid state amp repair for a friend (fender frontman 15G), experimenting again with the class-D as a "repair"/rebuild option, wondering why I can't ever get Class-D to work. Google helped me find out about the gain resistor mod on some audio forums, tried it, and found it worked great.
I'm not sure if I'll use it much or what I'll use this for, more of a utility / testing box I guess. Mainly just to see if I could get it working well.
Powered with an old laptop charger (19.5V, 3.5A), it is quite loud and sounds pretty clean. There have been many threads on this forum about others' builds, so I may be rehashing some comments.
Key Build Points:
-Removed the resistor on the TPA board from pin7 to pin8. (it was 100k on mine). The resistor from pin8 to GND is 39k, so according to TPA3118 datasheet page 14, the gain is set to 32dB. Online forums say that this internal gain is responsible for the HISS. Removing the 100k puts the gain at 20dB, and the hiss is gone.
-AMZ Mosfet booster in front to recover the gain lost from the resistor removal. I expected the Hiss may return when signal is boosted, but it did not. So, the hiss was being generated within the TPA at the higher gain.
-The AMZ booster is powered by the input power, through a L7809 (TO-220 package), with 100n to Gnd on the input and output. I lightly epoxy glued it to the side of the enclosure. The tab is touching, but not screwed to the enslosure, so the heat transfer is not probably not great, but the AMZ doesn't draw much current anyway.
-50kA volume pot between the booster circuit and the TPA board
-Output spearker jack must be isolated type. No sleeve to enclosure connection.
Here's my long project timeline:
-March 2021 - inspired by pedalpcb listing the TPA board, but it was out of stock, I purchased a fake TPA3118 board from amazon. Lots of hiss, and not actually that impressive loudness with various power supplies. Tried some buffers and boosts but never sounded good. I housed it in the white enclosure, but never used it.
-April 2026 - read about the existence of fakes and confirmed mine was the fake 28pin. Purchased another board from amazon, confirming in comments it's 32pin. Volume was stronger, but still loud hiss sound making it unusable to me.
-August 2026 - working on a solid state amp repair for a friend (fender frontman 15G), experimenting again with the class-D as a "repair"/rebuild option, wondering why I can't ever get Class-D to work. Google helped me find out about the gain resistor mod on some audio forums, tried it, and found it worked great.
I'm not sure if I'll use it much or what I'll use this for, more of a utility / testing box I guess. Mainly just to see if I could get it working well.
