Greetings.
I've started building an amp with salvaged parts and things where moving along nicely, but now I suspect I got some bad modules. Two modules seems to be very touchy on how they are grounded and sometimes pick up all kinds of junk on the output - like when I plug my Topping DM7 in the same outlet and turn it on the noise floor looks terrible. That is power only, no signal cable to amp. If I connect up signal cable it gets even worse. Then again if I remove all things from outlet, ground the input board to the module and feed it a signal from laptop via UMC204 in loopback it outputs a nice clean signal and noise floor looks good.
Seems to me there is some unstable components or defective filtering on the SMPS part of the modules. Both channels on both modules act the same. Third module works fine and doesn't give damn how its grounded or what else is going on, clean signal and noise floor no matter what.
If we look at the spectrum noise is clearly dominated by 100Hz, and lots of harmonics from there. So we have 230V 50Hz in the outlets here and 100Hz I guess comes from full bridge rectifier, but I'm not sure where to go from here. This is my first time with Class D and SMPS and no schematic available - Any hints at where to start?
I've started building an amp with salvaged parts and things where moving along nicely, but now I suspect I got some bad modules. Two modules seems to be very touchy on how they are grounded and sometimes pick up all kinds of junk on the output - like when I plug my Topping DM7 in the same outlet and turn it on the noise floor looks terrible. That is power only, no signal cable to amp. If I connect up signal cable it gets even worse. Then again if I remove all things from outlet, ground the input board to the module and feed it a signal from laptop via UMC204 in loopback it outputs a nice clean signal and noise floor looks good.
Seems to me there is some unstable components or defective filtering on the SMPS part of the modules. Both channels on both modules act the same. Third module works fine and doesn't give damn how its grounded or what else is going on, clean signal and noise floor no matter what.
If we look at the spectrum noise is clearly dominated by 100Hz, and lots of harmonics from there. So we have 230V 50Hz in the outlets here and 100Hz I guess comes from full bridge rectifier, but I'm not sure where to go from here. This is my first time with Class D and SMPS and no schematic available - Any hints at where to start?
Where do your modules come from?
We see quite a few for sale on Alli....
Counterfeit or downgraded ???
https://fr.aliexpress.com/item/1005...2551e9f43!12000034769261469!rec!FR!746260639!
We see quite a few for sale on Alli....
Counterfeit or downgraded ???
https://fr.aliexpress.com/item/1005...2551e9f43!12000034769261469!rec!FR!746260639!
Bad repairs or poor shipping protection? That has nothing to do with the problems here.
Where did you get the input modules from? and how are these wired up?
Care has to be taken in how the grounding is done on the inputs, I have had similar issues when hooking them up un-buffered - and not connecting the (different) grounds. Try to double check with the application note, also the one covering the add on amp module.
Clearly they are super quiet when hooked up correctly on the inputs - but I also notice that on 4ch amps with these, there is some extra mains filtering.
The input boards is also from aliexpress. I've studied them carefully under magnification and they do not seem counterfeit, also the input buffer opamps seems like genuine TI opa1678. All boards gives very low distortion.
In regards to grounding I have tried all kinds that I can think of, and no matter what there is a clear difference between the two "bad" modules and the one that is not affected by noise. With all my knowledge and equipment I can not find anything dirty or much ripple on psu. All of them gives same results.
I am currently wondering if there is possibility of two of the amps picking up EMI/RFI, since both has 100hz hum and both gets audible noise in speaker when other SMPS device is on same power outlet
In regards to grounding I have tried all kinds that I can think of, and no matter what there is a clear difference between the two "bad" modules and the one that is not affected by noise. With all my knowledge and equipment I can not find anything dirty or much ripple on psu. All of them gives same results.
I am currently wondering if there is possibility of two of the amps picking up EMI/RFI, since both has 100hz hum and both gets audible noise in speaker when other SMPS device is on same power outlet