• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 30 subscribers
  • Views 2072 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Headphone power amplifier TPA6120A2 - why is the output not loud very loud ?

John Lintern
Prodigy 80 points
Other Parts Discussed in Thread: TPA6120A2, TPS65136, TLV320AIC32

I am using the headphone amplifier (TPA6120A2) and it is not very loud, possibly because of my implementation and lack of understanding.

I need to drive a pair of headphone speakers which will be used in a noisy environment, so they need to be louder than average.  

Typical headphone amplifiers used in audio MP3 players and smartphones are not powerful enough, so I chose to use the TPA6120A2 hoping it would be louder, but it is no louder than the amplifier used in an iPhone/iPod.

I am using differential line outputs from a CODEC (TLV320AIC32IRHBT) as the audio source for the headphone amplifier (TPA6120A2).

The headphone power amplifier is powered using a DC-DC converter (TPS65136), which provides a +/-5V supply.  This is the same as figure 19 in the TPA6120A2 datasheet.

The DC-DC converter (TPS65136) is powered from a 3.7V, 850mAh lithium polymer battery.

The headphone power amplifier drives a pair of helmet speakers (TORK XPRO helmet speakers) which have the following specs:

  • Frequency range 20-22,000 hz at 106db/1KHz 
  • Max 500mW 
  • 32ohm

See...

http://www.torkworld.com/helmet-speakers/xpro-helmet-speaker.html

Some things I am unsure about are:

  1. Is the lithium polymer battery suitable ?
    1. Do I need a more powerful battery ?
  2. Is the +/-5V supply to the power amplifier suitable ?
    1. Do I need a higher voltage split rail supply ?
Are the line outputs from the CODEC suitable ?  
  1. The TPA6120A2 datasheet shows an example using a PCM5242RHB CODEC which has 4.2VRMS, ground-centered differential outputs.
  2. From my understanding, the TLV320AIC32IRHBT datasheet specification states that the differential outputs are 0.707VRMS, 1.35V centered  (is this correct ?)
Are the helmet speakers/specifications suitable ?
  1. The manufacturer (TORK) states that these headphones "can plug into all popular music devices such as MP3, iPOD, Galaxy and iPhone".  The speakers weren't very loud when I tried them with my iPod, I am assuming its because the amplifier in the iPod isn't driving the speakers to their full potential ?

  • 0
    TI__Guru* 98565 points

    Hi John,

    +/-5V supply should let your output have an amplitude of around 5V into 32Ohm loads.
    0.707Vrms is the rated output voltage for a single output of the differential pair of TLV320AIC32. The difference of the differential signals should provide a total output of 1.414Vrms as shown in the following table from the datasheet.

    What is the output that you're expecting?
    What is the gain of the TPA6120A2 in your setup?
    What is the input signal to TPA6120A2?

    Best regards,
    -Ivan Salazar
    Texas Instruments

  • 0 in reply to Ivan Salazar
    Prodigy 80 points

    Hi Ivan, thanks for your reply.

    I am not sure what output power rating to expect,  but the helmet speakers are specified as 500mW (it doesnt state whether this is peak or rms) and 32 ohms.

    Is the gain of the TPA6120A2 defined by the resistors ?  If so, then I have used the same resistor values as shown in figure 19 in the TPA6120A2 datasheet....

    The input signal to the TPA6120A2 is from the line output of the TLV320AIC32IRHBT CODEC.

    The configuration of the TLV320AIC32IRHBT (configured via I2C) can be found in the attached spreadsheet I2C.xls.

    I2C.xlsx

  • 0 in reply to John Lintern
    TI__Guru* 98565 points
    Hi John,

    Yes the gain is defined by feedback and input resistors. Feedback resistors are the ones that go from LOUT to RIN- and ROUT to RIN- and Input resistors are the ones connected from LIN+ and RIN+ to GND.
    You could reduce the value of the input resistors or increase the value of the feedback resistors in order to increase the gain. The gain by using Input and Feedback resistors as 806 is 1V/V.
    I'll take a look at the TLV320AIC32 configuration you've attached.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Prodigy 80 points

    Thanks Ivan

    I have tried increasing the LEFT_LOP/M Output Level Control / RIGHT_LOP/M Output Level Control in Page 0 / Register 86 and Page 0 / Register 93 from 0dB to 8dB.  

    This made the output louder, but the qulaity doesn't sound as good as the amplifier in the CODEC (TLV320AIC32).

    It also completely drained the 3.7V 850mAh battery within 10 minutes of use !!!  So does that mean the battery capacity is not large enough for this application or is there an issue with my setup ?

    Something else I thought of trying.... as I am only using one headphone speaker at the moment, could I use the TPA6120A2 in BTL (bridge terminated load) configuration ?

    The CODEC (TLV320AIC32) datasheet states that it can be used in BTL configuration, so I was wondering whether I should try this with the CODEC first of all.

    If the CODEC amp is still not loud enough in BTL configuration, then would it be possible to use the TPA6120A2 in a BTL configuration ?

    Also, could you please explain how to use the CODEC in the BTL configuration (and the TPA6120A2 if applicable) ?

    For the CODEC I have...

    • HPROUT going to the right headphone speaker
    • HPLOUT going to the left headphone speaker
    • GND going to the ground headphone speaker

    ...as shown in the attached schematic.  How do I connect one headphone speaker (left or right) to use the BTL configuration?  There is no information in the CODEC (TLV320AIC32) datasheet.

  • 0 in reply to John Lintern
    TI__Guru* 98565 points
    Hi John,

    Technically you could setup the TPA6120A2 into BTL output by inverting the input of one of the channels.
    Regarding the BTL on TLV320AIC32 I think it should be something like 8 Ohm speaker in Figure 15 from datasheet page 16.
    I will take a look at your register configuration along with one of my colleagues who is currently in charge of supporting this codec and come back with configuration recommendations for BTL output.

    Best regards,
    -Ivan Salazar
    Texas Instruments