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TPA6140A2: Audio Line Driver and I2C Volume Control for PCM5242? Using Headphone Amp as Line Driver?

Jay Shoemaker
Intellectual 650 points
Part Number: TPA6140A2
Other Parts Discussed in Thread: PCM5242, , , TPA6130A2, TLV320AIC3105, PCM4104, TAC5212

Hello, 

I have a PCM5242 DAC in which I would like to control two separate line-level (2VRMS) outputs with discrete volume controls for each output. I would like to control the volume of each stereo output pair using I2C control. Can I use two TPA6140A2 units to add analog volume control to those two separate outputs (with an I2C multiplexor so I can control each separately)?

What will the total VRMS output of the TPA6140A2 be? Would it be "too hot" to drive a standard 10k input pin on a consumer device for example? Is there a way that I can keep the TPA6140A2 volumes low so that it doesn't overload the inputs on the receiving device? 

The TPA6140A2 has a "tapered volume" control which is nice. But that means that I really shouldn't just "limit" in software the maximum height of the volume level, because I would then lose the tapered control benefits. So I guess I would have to turn the gain down sufficiently so that at 100% volume, the TPA6140A2 is only driving 2VRMS out, to not overload the input on the receiving device. 

Any ideas on this? Are there any other products that would work as a line driver with I2C volume control in the sub $1 range?

Thank you, 
Jay

  • Intellectual 650 points

    PS - I know the TPA6130A has tapered volume control but does the TPA6140 have that too? I guess if it's not tapered, I could technically limit in software the max volume, but then I will lose resolution, still. 

  • Intellectual 650 points

    I think probably the answer to my question is that I can use this but I probably want to attenuate the signal using a Pad. On the TPA6140A2EVM schematic there is a pad on the outputs. These are jumped with 0 Ohm resistors but I think for my application I should populate them with the correct pad to attenuate to my specified line-level output.  

    I will be using these as a differential line driver so OUTL will be regular and OUTR will be inverted (for a balanced line out). I'm pretty sure I'll want approximately 1VRMS on each pin to create "2VRMS" with the differential pair.

    I'm unsure of the calculations that I need to determine what size pad I would need. I know that I'm trying to drive a standard line-input as opposed to a headphone so it will have 10k Impedance, and I want approximately 1VRMS. I asked Chat GPT and it said that I should put a 21dB pad on the outputs.

    Does this sound about right?

  • Intellectual 650 points

    Maybe this would be about right for my balanced line driver use?

  • in reply to Jay Shoemaker
    TI__Guru** 100475 points

    Hi Jay,

    I'm a bit lost on the question here. PCM5242 already supports differential line-driver outputs, what's the purpose of adding TPA6140A2 in front of it only to be used as differential line-driver again? PCM5242 also supports digital volume control, so any gain could be applied on PCM device itself?

    I would rather set a fixed gain/attenuation in one of the devices and then only adjust the gain on the other device, instead of adding external circuitry just to bring the signal down as it would increase the system current consumption unnecessarily.

    Hope this helps, let me know if I'm missing something.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • in reply to Ivan Salazar
    Intellectual 650 points

    Hello Ivan,

    I hear your point but I assure you I have good reason. :-)

    I want to use the DAC to drive headphones, and master outputs. Both of these outputs require individual volume control. The headphone and master have the same signal but different volumes at any given time - according to room or user preferences. Changing the volume on one should not change the volume on the other. 

    The use of the PCM5242 is arbitrary, actually. It could be any DAC for this example. But having the DAC power a headphone amp (monitor),  and line driver (master) at the same time just saves money by not having to add another DAC to drive separate volume controls. 

    I'm surprised there is no i2c controlled line driver with volume and gain! It would be a useful product for sure and definitely falls within the TI wheelhouse. Make it Directpath and you have a winner. 

    In my case I have the PCM5242 driving the master outs, and it is also tied to a TPA6130A2 for the headphones. However, changing the (digital) master volume will adjust the monitor outputs too. The only option for me in this case is another PCM5242 receiving the same serial audio data, but different i2c commands so it's a fixed volume. This would in theory would give me individual control over master and headphones. But it comes at the cost of having two DAC's instead of one. 

    Are there any other products I can look at for this? I also have been toying with a TLV320AIC3105 device and that is nice because it has different output mixers and volume controls for each of the (8 or so) outputs. But it's quality is not as good as the PCM5242. I guess I just wish that I had a higher quality TLV codec (114dB+), or some discrete front end Directpath driver IC's to "make my own" configuration as described above. 

    Thanks for your input,

    Jay

  • in reply to Jay Shoemaker
    TI__Guru** 100475 points

    Hi Jay,

    Are both headphone and line supposed to be operating simultaneously?
    I assume you need differential line driver, is that correct? Otherwise, you may just use the headphone amp to drive either headphone or single-ended line output.

    Individual gain control with a single DAC seems complicated, even if you drive the line outputs directly from PCM5242 and headphone only through TPA6130A2, whenever you change the gain for line outputs you would have to adjust the same on headphone amp to compensate for it.

    Perhaps you should look at higher channel count DACs, like PCM4104? Then you can use a pair of differential outputs with fixed gain to drive the headphone amp, and the other pair with variable gain for line outputs.

    What is the timeline of your project? Would you be interested in new devices being released by mid next year?
    You can get an idea of this device (TAD5x12) from his evaluation tool: https://www.ti.com/tool/TAC5112EVM-K

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • in reply to Ivan Salazar
    Intellectual 650 points

    Hello Ivan, 

    Thank you for your response. I'm hoping to have a product within 6 months time, but it can vary + or -. I'm not sure of your timeline on the new products. While the TAD devices aren't exactly what I need The TAC5212 is actually perfect. I submitted a request to test the evaluation, and if you have any pull please get me one. It seems like maybe the perfect solution for my product. Thanks!

    Jay

  • in reply to Jay Shoemaker
    TI__Guru** 100475 points

    Hi Jay,

    Good to know the new devices fit well on your applicaiton.
    I'll follow up internally with the team to identify your request.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • in reply to Ivan Salazar
    Intellectual 650 points

    Thanks Ivan,

    I also want to point out that an I2C controlled line driver which contains the exact same front end as the TAC5212 (for example) would still be a useful product! Placing multiple line drivers, headphones amps, speaker amps, etc on one DAC would save money and power consumption. 

    As an audio enthusiast and engineer, I believe controlling headphones and master outputs as different zones and having different volumes makes sense. I've always been surprised that a simple I2C low cost line driver with volume and gain doesn't exist in the TI portfolio. The existing products are way too costly. We need a cheap volume control! Maybe it could also serve as an input filter/driver for ADC's, too. 

    Yes I can use multiple DAC's... And will likely do that. But discrete front ends on a single stereo DAC would be theoretically cheaper (and possibly more power conscious). It's basically what the TLV320AIC3105 devices are. They have multiple inputs and outputs but only stereo DAC/ADC. 

    Have a happy new year!

    Jay

  • in reply to Jay Shoemaker
    Intellectual 650 points

    Ivan, 

    I mistakenly asked for the 5242 and then realized it was Hardware control only. I really would like the I2C control of the 5212. I have two cases, but the case which was accepted was the wrong model. I don't know where to contact Mark Ursua about this, the reply email is just support@. 

    Case CS2146671 and CS2146667. 

    Please modify my case if you can. Thank you. 

    Jay

  • in reply to Jay Shoemaker
    TI__Guru** 100475 points

    Hi Jay,

    You may just submit a new request for the proper part number, I see you listed 2 case numbers, is it one for each device?

    Best regards,
    -Ivan Salazar
    Applications Engineer