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OPA1632: the specific improvement via using FDA in audio system

Part Number: OPA1632
Other Parts Discussed in Thread: OPA1678, , NE5532

Dear team,

In professional audio application, there are a lots of people using the FDA such as OPA1632 to do the conversion of single to differential or XLR line out. For example, driving the audio ADC or audio power amplifier (long wire maybe.) We both know that the FDA could reduce the common mode noise and improve THD because the output signal will be more symmetrical, but I am always about how much THD(dBc) could be improved and how much noise could be decreased comparing with the differential driving circuit achieving by 3 or 2 opamp (NE5532,OPA1678...).

1. Have you done any testing to compare the performance?if done, could you please share with me about how much performance could be improved (general number about THD,noise)?

2. Withour testing, is there any theory or skills to roughly calculate how much THD and noise can be improved if the differential signal circuit is achieve by FDA instead of opamp?

3. Is there any other benefit in the audio system if the FDA is applied? can these benefit be calculated roughly?

Best regards

Zhihong Huang

  • Hi Zhihong,

    These are very interesting ideas, however there is no definitive calculation to quantify the performance benefits of an FDA vs a regular amplifier. There is simply too many variables and unique cases making it difficult to directly answer a question like this. The theory to why an FDA is beneficial, however, is available and I have it attached here. The detailed application note highlights the benefits of this architecture in audio along with other applications. 

    I would also like to reference two separate articles where discrete versions of single-ended to differential output circuits are highlighted. One article does give some DC and AC results of the circuit and can be found here. The other article highlights how to configure the circuit and can be found here. However, as was mentioned there is too many variables and design spec differences for a direct comparison and calculation to be derived.

    Best Regards,