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Beocreate : DAC output and TPA3128 gain

Alic Loeliger

April 28, 2020 15:21

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Hello,

In order to prevent clipping with reduced supply voltage, I would like to know what the max RMS voltage output is of the DAC before the amp input and which gain (from 20dB to 36dB) has been selected for the desing of the amps? Where can I find this information?

If the DAC is the same as the Pro model, the output is probably 2.1V RMS max in which case the lowest gain of 20dB would be the best option for the amps to avoid loss of audio quality from excessive volume reduction in software. This also means that a supply of minimum 21Vdc is a good idea to prevent clipping at hight volume levels.

Thanks in advance for your support.

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6 comments

• 0
  
  HiFiBerry team April 28, 2020 15:27

  Amplifier gain is 20dB, max output of the internal DAC is a bit less than 2Vrms. 
  
  You probably won't run at volumes anything close the maximum power.

• 0
  
  Alic Loeliger April 28, 2020 20:08

  Thanks fo the information and the fast reply.

  The gain seems too high for the ouptput of the internal DAC.

  At max volume it's a bit less than 20V RMS output (or +/ - 28V peak), which is too much for the amps in all situations since the highest supply voltage is 24Vdc and the power will be too high anyway to remain below the 10% THD mark. Less than 1.5V RMS output would have been ideal for the internal DAC.

  My problem is that the supply voltage of the battery i planned to use drops from 21V to 13V over time. To avoid distortion and clipping I would have to use this 13V value for the maximum voltage. This means that the volume at the output of the DAC has to be lowered from the 1.8V or 1.9V RMS max value to less than 0.9V RMS and this would be the maximum value.

  I will add more capacity to the battery and discharge it only down to 17V. This seems to be an acceptable compromise.

  It's not clear for me if there is a way to lower the volume on the Beocreate without loosing quality?

• 0
  
  HiFiBerry team April 28, 2020 20:12

  You can simply reduce the volume. You won't "loose" quality by reducing the output level by a few decibels. While this might have theoretical implications, there aren't any practical. As long as you don't reduce the output level bei 20db or more, you won't notice any changes in dynamic range at all.

• 0
  
  Alic Loeliger April 28, 2020 20:25

  Ok thanks, I will try it to see what happens.

• 0
  
  Peter July 28, 2020 03:27

  I have been looking everywhere for this gain information. Maybe it should be in the hardware specification? Can HiFiBerry confirm that the 20dB gain is true for both the 30W and the 60W BTL channels?

  I have just started using the Beocreate 4 to implement 3 way active crossovers in a stereo system. It's much harder to implement cost-effectively a pair of 3 way crossovers than 2 ways, but routing the spdif output to an external optical DAC and using the power of Sigmastudio gives a pretty good solution and lets me treat the Beocreate as a 2 in X 6 out system with all volume control, filtering and equalization integrated in the one DSP. I couldn't really do this with MiniDSP boards and their closed DSP signal flow. I am really pleased with how flexible the Beocreate 4 /Sigmastudio combination is and I am hoping to be able to add headphone equalization and crossfeed to the project, by time sharing the external DAC.

• 0
  
  HiFiBerry team July 28, 2020 04:49

  Yes, that's correct.