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INA217 Audio Amplifier Circuit Modifications

jb9475
Prodigy 20 points

Other Parts Discussed in Thread: INA217, PGA2310

I'm working on a design for an audio mixer for a small recording studio and have succesfully tested the schematic for the INA217 published as Figure 4 on page 7 of the TI data sheet: http://focus.ti.com/lit/ds/symlink/ina217.pdf
I'm very pleased with the response of the published circuit, but I'd like to do a few modifications:
1.  I'd like to provide an alternative input for an unbalanced, high impedence source (i.e. electric guitar, etc.) so that the circuit could be run on either source.
2.  I'd like to add a pad or "trim" control in front of the IC to prevent a source signal that is too "hot" from overdriving the IC.
3.  I also wonder if the gain control potentiometer, R7, could be eliminated, leaving R6 at a fixed value of 8 ohms, to run the IC at maximum gain, then adjusting the volume with a variable resistor in series with the output of the IC.  This would allow for other subsequent stages at the output side including EQ, AUX I/O effects, etc. before hitting the main fader.
Comments please!

  • 0
    TI__Intellectual 2970 points

    1. INA217 will work with balanced as well as with unbalanced source signal.

    2. You can add resistive voltage divider  which will lower input signal and limit input current. This works well in combination with protective diodes from Figure4 on page 7 of the INA217 data sheet.

    3. It is possible to keep R6 at a fix value. You can use PGA2310 on the output of INA217 for volume control. http://focus.ti.com/docs/prod/folders/print/pga2310.html

     

  • 0 in reply to Miro Oljaca
    Prodigy 10 points

    It is possible to connect V+ to 5V and V- to 0V in order to be able to connect an INA217 directly to a microcontroller?

    Do they necessarely have to be connected simmetrically (+V and -V)?

    Thank you!!!

  • 0
    Prodigy 20 points

    Hello -

    I'm no genius in this area so I'll leave that up to the experts who may respond to this post, but I can refer you to the TI data sheet: http://focus.ti.com/lit/ds/symlink/ina217.pdf

    The circuit is on page 7.  What I do see is that by altering the polarity of the power to this circuit you may be limiting the functionality of the individual IC's on that chip.  In other words, you may get some limited response by altering the supply voltage in this way, but until you breadboard this circuit and try your altered supply voltage ideas, you may not know how those supply voltages actually affect the response of the INA217.

    Our application involved an audio mixer design.  We resolved the balanced/unbalanced issue by maintaining the integrity of the TI engineered circuit (referenced above) and using common I/O transformers to alter both the impedence and the balanced/unbalanced signals.

    Our second issue was to prevent overload to the input stage which could lead to distortion.  We did that with a 1M ohm audio taper pot across the input to prevent the source signal from overdriving the IC.

    Our third concern was about eliminating the gain control pot and trying to control the output during a later stage, and we found that the gain control pot shown in the circuit is necessary to prevent distortion from overloading the IN217.

    Good luck with your project, and please post your results!

    Jim

  • 0 in reply to jb9475
    Prodigy 10 points

    It is best to keep a gain control on a mixer first stage. This allows you to preset the channel gain and maintain good signal to noise and good headroom (ie avoid clipping) for a wide range of sources that you might wish to connect.

    The INA217 spec sheet shows minimum power requirement of +/-4.5V. Therefore the minimum single rail to achieve the performance in the spec would be 9V.

    You then need to provide a mid-rail reference for the input circuitry to achieve good voltage swing.

    What is the actual PIC interface problem that you are trying to solve?

  • 0 in reply to Tony Martin47793
    Genius 3945 points

    Tony Martin said:

    It is possible to connect V+ to 5V and V- to 0V in order to be able to connect an INA217 directly to a microcontroller?

    Do they necessarely have to be connected simmetrically (+V and -V)?

    Thank you!!!

     

    The rails don't have to be symmetric, but RTFS: the output can swing from VCC - 2V to VEE + 2V. So your headroom on a single 5V rail is very limited.