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OPA551: OPA 511 as headphone amplifier - single supply - balanced inputs

Matteo Bonino
Prodigy 80 points
Part Number: OPA551

Tool/software:

Hi, I'm in the process to design a headphone amplifier, as part of a hifi preamplifier. I thought this could be based on the OPA551, which I see is widely available. I see the performances are impressive.

My requirements are: 

- single power supply available  (28 Volt), about 80-100mA per channel

- balanced input

- capability of the integrated circuit body to be easily heatsinked (like the OPA551 in TO-263 case), as I'm always concerned about reliability - temperature. This for example made me exclude the TPA6120A2DWP, another interesting option

- little bit of gain, about 2 in the example

- capability to drive 16 to 600 Ohm headphones

- as the power supply is somewhat limited to 2.5 Watt per channel, I'm not interested to the ultimate in terms of sound pressure, a good 200mW would be more than enough.

This is the design I defined, I'd like to ask your opinion with regards to: stability, and utilization of single supply (as you can see I've biased the two input signals at 14V, with 3.9K precision resistors. It means 3.5mA additionally drawn, I'm fine with that).

thanks so much in advance

A good day

Matteo

  • 0
    TI__Genius 12316 points

    Hi Matteo,

    Sorry for the delay. R173 and R175 will cause issues with the circuit as these resistors will form another resistive path from the feedback loop to GND. R176 and R174 will bias the common mode of the OPA to a voltage which is not 14V as R10 and R171 make this a larger voltage divider. 

    The best way to make this circuit functional and symmetrical is to make R171 a voltage divider .

    See my example below:

    You are right, the TO packages make it very easy to throw a heatsink on if you want to easily lower the case temperature of the device. 

    What is the load on the preamp after C54 and C55? 

    Thanks,

    Jacob

  • 0 in reply to Jacob Nogaj
    Prodigy 80 points

    Thanks so much for the hints ! I well noted how the voltage divider works, understood. This will be implemented as headphone power amplifier, so the load after C54 and C55 will be a wide potential range from 16 Ohm to 600 Ohm. Cheers

  • 0 in reply to Matteo Bonino
    TI__Genius 12316 points

    Hey Matteo,

    Perfect, that impedance range will work well. 

    My simulations show that this will work well with OPA551:

    Please let me know if you have any other questions.

    Thanks,

    Jacob