Balanced output from AD1937

Hi there,

I would like some assistance with an AD design for the balanced outputs from the AD1937 codecs.  The reference designs I have seen, and on our evaluation board, are typically for unbalanced audio outputs with OpAmps.  We need all outputs to be balanced audio outputs.  Ideally achieving +18 dBu at 0 dBFS within the codec.  i.e., trying to set the maximum output voltage to +18 dBU (~6.15 Vrms), for connection to external audio devices.

Can you please provide me with your recommended parts/schematic to achieve this?

Kind regards,

Mark

Parents
  • Hello Mark,

    This is a good question. I just checked around for designs on different eval boards and others that were never released and we do not have any designs that keep the audio balanced. Our eval board for the ADAU1966 just has passive filters and then connects that to a dSub as a differential output. No Opamps. Most of the time our customers will take the output of the DAC and process it through level controls, faders,  or send it to amplifier chips so the signal needs to be single ended. 

    Thinking about this you would want to filter the outputs so simply treating each N & P output as a single ended output is probably the simplest way to do this. Here is the single ended filter out of the AD1938 datasheet:

    So duplicating this for each "N" and "P" output would give you a filtered differential signal with a fair amount of drive. Then add one more amp stage to gain up the signal up to get the +18dB signal you are looking for. You will need to have at least +/-12V power rails but I think you know that. 

    I like a 2-stage approach so the filter can be a clean and good design then get the gain out of the next stage. 

    You may want to post a question up on the Linear Amplifiers portion of the forum. They are really good at OpAmp designs and know our Op-Amp catalog better than I do. I would probably start with the Amplifiers Homepage: (+) Amplifiers - EngineerZone (analog.com)

    Dave T

Reply
  • Hello Mark,

    This is a good question. I just checked around for designs on different eval boards and others that were never released and we do not have any designs that keep the audio balanced. Our eval board for the ADAU1966 just has passive filters and then connects that to a dSub as a differential output. No Opamps. Most of the time our customers will take the output of the DAC and process it through level controls, faders,  or send it to amplifier chips so the signal needs to be single ended. 

    Thinking about this you would want to filter the outputs so simply treating each N & P output as a single ended output is probably the simplest way to do this. Here is the single ended filter out of the AD1938 datasheet:

    So duplicating this for each "N" and "P" output would give you a filtered differential signal with a fair amount of drive. Then add one more amp stage to gain up the signal up to get the +18dB signal you are looking for. You will need to have at least +/-12V power rails but I think you know that. 

    I like a 2-stage approach so the filter can be a clean and good design then get the gain out of the next stage. 

    You may want to post a question up on the Linear Amplifiers portion of the forum. They are really good at OpAmp designs and know our Op-Amp catalog better than I do. I would probably start with the Amplifiers Homepage: (+) Amplifiers - EngineerZone (analog.com)

    Dave T

Children