I have built a 10-channel power amp using LM3886's on Rod Elliott's PCB. I have a big shared power supply (1kVA transformer, 112000uF, etc).
I am getting between 13 and 50mV pk-pk of sharp spikes on the output (sounds like mains related buzz), co-timed with the charging spikes on the supply rails (about 350mV pk-pk sawtooth on 32V rails). Channels where the noise is below 20mV pk-pk are almost acceptable, but the one channel that is up at 50mV is a real problem.
Does anyone know where this pick-up is likely to be happening, and what I might be able to do to lessen its effect? Power supply rejection on the LM3886 is supposed to be 85 to 100dB - I am certainly not achieving this. Any clues as to why there could be such variability between channels? (doesn't correlate with position in chassis relative to power supply)
Many thanks
Jamie
I am getting between 13 and 50mV pk-pk of sharp spikes on the output (sounds like mains related buzz), co-timed with the charging spikes on the supply rails (about 350mV pk-pk sawtooth on 32V rails). Channels where the noise is below 20mV pk-pk are almost acceptable, but the one channel that is up at 50mV is a real problem.
Does anyone know where this pick-up is likely to be happening, and what I might be able to do to lessen its effect? Power supply rejection on the LM3886 is supposed to be 85 to 100dB - I am certainly not achieving this. Any clues as to why there could be such variability between channels? (doesn't correlate with position in chassis relative to power supply)
Many thanks
Jamie