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Good day.
I'm troubleshooting a mackie srm 350/450 V3 speaker, which makes a high pitch whine/noise.
The amp plate unit consists of quite a standard power amp section, which is used across multiple other mackie models (switching mode power supply + TDA8954 for the LF and TDA7294V for the HF and of course the auxiliary power rails - +/-15V, +12v) and an input/pre-amp board.
I also have an older mackie speaker so was able to switch boards and the analog only input/pre-amp board does not hiss/whine with any of the power amps and vice versa - the V3 preamp board is noisy with both of the power amp boards.
This leads me to believe that the problem is with the V3 input/pre-amp board.
What is on the preamp board - basically two channel inputs with volume control, adc/dac ic, DSP ic, human interface controller ic (switching leds, registering button presses, etc.) and power management ics.
The audio signal flow is: input connectors - few opamps - volume control - more opams with filtering and limits - adc - dsp - dac - another opamp with some filtering.
Power rails - the dac/adc IC uses +5v, which is generated from the +12ish rail from the power amp by a dedicated IC. The dac/adc also uses +3.3 rail, which is generated by a switching IC that also generates the +1.2 rail for the DSP. +3.3v rail is also used by the DSP and the "interface controller". Op-amps directly use the +/-15 rails from the amp board.
The issue - constant hiss/noise/whine, which is not affected by volume level. The noise appears after the DAC. The final op-amp seems to filter it for the LF, but not for the HF.
I cannot determine if the noise is coming from the adc/dac IC, the DSP or from bad communication between that ICs.
Something that I have noticed is a "noisy" +1.2v rail when compared with the the +5 and +3.3 ones.
I've tried fixing it with changing the output caps with low ESR ones, changing the coil L7 and even switching it with L3, but the noise/ripples stay.
What I have changed so far (all new caps are low ESR):
C41
C195
C238
C37
L7
L3
C67
C68
C230
C36
U11 (final op-amp)
Here you can hear the noise (remove the spaces)
mega . nz / file / MdQBwBLA#S8ojJG4Pk_qftWMznXTv3SXh5cGqc6jYzkzjnc4X2-M
I'm troubleshooting a mackie srm 350/450 V3 speaker, which makes a high pitch whine/noise.
The amp plate unit consists of quite a standard power amp section, which is used across multiple other mackie models (switching mode power supply + TDA8954 for the LF and TDA7294V for the HF and of course the auxiliary power rails - +/-15V, +12v) and an input/pre-amp board.
I also have an older mackie speaker so was able to switch boards and the analog only input/pre-amp board does not hiss/whine with any of the power amps and vice versa - the V3 preamp board is noisy with both of the power amp boards.
This leads me to believe that the problem is with the V3 input/pre-amp board.
What is on the preamp board - basically two channel inputs with volume control, adc/dac ic, DSP ic, human interface controller ic (switching leds, registering button presses, etc.) and power management ics.
The audio signal flow is: input connectors - few opamps - volume control - more opams with filtering and limits - adc - dsp - dac - another opamp with some filtering.
Power rails - the dac/adc IC uses +5v, which is generated from the +12ish rail from the power amp by a dedicated IC. The dac/adc also uses +3.3 rail, which is generated by a switching IC that also generates the +1.2 rail for the DSP. +3.3v rail is also used by the DSP and the "interface controller". Op-amps directly use the +/-15 rails from the amp board.
The issue - constant hiss/noise/whine, which is not affected by volume level. The noise appears after the DAC. The final op-amp seems to filter it for the LF, but not for the HF.
I cannot determine if the noise is coming from the adc/dac IC, the DSP or from bad communication between that ICs.
Something that I have noticed is a "noisy" +1.2v rail when compared with the the +5 and +3.3 ones.
I've tried fixing it with changing the output caps with low ESR ones, changing the coil L7 and even switching it with L3, but the noise/ripples stay.
What I have changed so far (all new caps are low ESR):
C41
C195
C238
C37
L7
L3
C67
C68
C230
C36
U11 (final op-amp)
Here you can hear the noise (remove the spaces)
mega . nz / file / MdQBwBLA#S8ojJG4Pk_qftWMznXTv3SXh5cGqc6jYzkzjnc4X2-M
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