I have a tda7498e amp board that has a high noise floor and the only was I can describe the noise is as a staticy hiss. This is coming from the amp board itself because it happens whether the inputs are connected or not. I am using a 36v 10a SMPS to power it so to rule out noise from the power supply I tried it with a tpa3255 amplifier board and its quiet on that board. The tda7498e has noise with every power supply I tried including 2 different laptop 19v psu's and an unregulated ring transformer. I think I narrowed it down to the 50k volume pot on the board, or at least the pot is contributing or interacting somehow. When the pot/volume is turned all the way down the noise floor is extremely quiet/almost non-exsistant but as soon as you start turning the volume up the noise gets louder and louder. I then tried removing the pot entirely and placed a jumper on the board connecting the pots pins 1 & 2 and the noise is still there! So now I am stumped as to what to do next. The circuit is based on the datasheet layout except for the addition of the 50k pot.
The pot is in between the 1uf and 1nf caps.
The pot is in between the 1uf and 1nf caps.
Attachments
Well I removed it entirely now and the noise is still there as if the pot was turned up high. The gain is configured at the lowest setting around 25db if I remember correctly. At this point I don't know if there's something wrong with the IC itself or there's something causing it that I'm doing.
I'll try and ground them as well as pins 32&33 because they're also used it's a 2 channel design. Not sure I'll be successful because the pins on the chip are so small.
Shorting c3 and c13 will short left and right positive inputs to ground, should I also short the negative inputs to ground or will that not matter since it's already connected to ground?
Well it got a little better when shorting the inputs after the pot. I ended up installing a ring terminal around the shaft of the pot and connected the other end to the audio input ground. It's as good as it's going to get at this point I'm afraid. Doing a little more reading online seems like the tda7498e chips are known to be noisy. I guess another tpa3255 is on my future to do list.