Hi,
I got one of these TDA8954 HiFi 210Wx2
When the onboard volume control is between about 9 and 12, there's a low motorboating sound from the speakers. No sound when the volume is turned down, nor when it's turned up. Only in that 9-12 region. Open inputs.
Any ideas?
I got one of these TDA8954 HiFi 210Wx2
When the onboard volume control is between about 9 and 12, there's a low motorboating sound from the speakers. No sound when the volume is turned down, nor when it's turned up. Only in that 9-12 region. Open inputs.
Any ideas?
No, 0 volt not yet earthed. Just testing it at the moment. Haven't put it into a cabinet etc. Was planning to use a ground isolator (bridge)
The reason: Extremely bad grounding scheme. On my board I had to rearrange (cut, and reroute) the entire rear of the PCB. The return path of the filter cap's current is modulating the input ground potential. After the mod the buzzing is gone. Zero noise, at both minimum and maximum volume settings. Not an easy task, but worth it... 🙂
Hmmm....but in my case, it's silent at zero and max. The motorboating sound is only when the vol control is between about 9 and 12.
Unfortunately describing it step by step not so easy. Basically the standard grounding rules apply, do not lead the the filter cap ripple current path together or close with the signal ground. As you see it is a kind of star grounding, separate wires from the speaker return ground, filter cap commons, and input signal earth point.
The common point is the transfo center tap (blue wire) on the upper left corner.
The rectifier bridge also replaced with Schottky diodes (SB 5100), plus the 10 filter capacitors increased from 1000 to 1500 uF. My supply voltage is +/- 24 V, (DC) so 25V filter caps can be used (Panasonic FR). If you are not familiar with working on double sided PCB-s , be very careful, the space is limited and the foil patterns are rather fragile....
The common point is the transfo center tap (blue wire) on the upper left corner.
The rectifier bridge also replaced with Schottky diodes (SB 5100), plus the 10 filter capacitors increased from 1000 to 1500 uF. My supply voltage is +/- 24 V, (DC) so 25V filter caps can be used (Panasonic FR). If you are not familiar with working on double sided PCB-s , be very careful, the space is limited and the foil patterns are rather fragile....