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Audio Preamplifiers

Suneetha Vadlapatla
Intellectual 260 points

Other Parts Discussed in Thread: TL971

Dear Sir/Mam,

My worked domain is Digital previously but I have to work on Audio Amplifiers Concepts.I have little knowledge on op-amps.

I need some support on the Audio Preamplifiers.Can I use TL971 for audio preamplification of Audio CODEC signal of VS1053 device?.I need the CODEC signal amplification to Line Level (1.8V Peak).Can anyone suggest the circuit of TL971 with single supply operating on 5V Supply?The output of this preamplifier should drive to Audio Power Amplifier (LM4780).

My audio chain is like this

Audio CODEC(VS1053) ---> Audio Preamplifier ---> Power Amplifier (LM4780).

Waiting for response.

Suneetha.

 

  • 0
    TI__Guru**** 174676 points

    Suneetha,

    I don't know the peak level for VS1053 device. How much voltage gain is desired?

  • 0 in reply to Ron Michallick
    Intellectual 260 points

    Hello Ron,

    The Analog characteristics of VS1053 from the datasheet are as follows

    Full Scale Output Voltage (Peak-to-Peak)  --- 1.64Vpp(Min)   1.85Vpp(Typ)     2.06Vpp(Max)

    From the above data I did the calculations like this as

    Peak Voltage is  --- 0.82Vp(Min)   0.925Vp(Typ)   1.03Vp(Max)

    Required Audio Line Level voltage(+4dBu level) - 1.8V Peak

    Gain in dB  = 20 log(Output Voltage/Input Voltage) = 20 log (1.8/0.925) = 5.78dB

    Is it the right way of doing calculations for audio side as the audio signal will not have stable states like as digital (High-Low Levels)?

    If it is right,suggest the IC for preamplification purpose Sir.

    Suneetha.

  • 0 in reply to Suneetha Vadlapatla
    TI__Genius 14487 points

    Suneetha,

    Attached is a schematic of an operational amplifier configured as a non-inverting amplifier. The gain, Av (unitless), may be calculated by Av = 1 + RF/RG. Use resistor values in the kilo-Ohm range. Since your desired gain is close to 2, that means RG = RF, so two 10 kOhm resistors may be used (or your choice). This should work well on a 5 V supply so long as your input signal does not drop below 0 V.

    James

  • 0 in reply to James Lockridge19
    Intellectual 260 points

    Hello James,

    Thanks for giving design support.What is your suggestable IC for this circuit to do the audio preamplification?Have I need any capacitor at the output as the is not operating on split Power Supplies, only operating on 5V DC Supply.?

    This output signal should drive to our LM4780 which is a Audio Power amplifier.

    Suneetha.

     

  • 0 in reply to Suneetha Vadlapatla
    TI__Genius 14487 points

    Suneetha,

    I was just speaking with Ron (from the second post), and he advised a different circuit for the TL971, pictured below. This circuit is an inverting amplifier with a gain of 2 (Av = -Rf/Ri = -20k/10k = -2). Even though the signal will be inverted, this should be fine for an audio signal.

    The reason for using this circuit is because the input common mode range for the TL971 is 1.15 V to 3.85 V for a 5-V single supply. The circuit below creates a DC bias at the inputs of 2.5 V, which is well within the common mode range.

    To answer your most recent question, yes, you do need a capacitor (and a resistor to ground) on the output. I've included that in my schematic as well. The output from the circuit below should be able to go straight to your input of the LM4780. As a note, the capacitor and resistor values on the output should work, but they may need to be adjusted based on your LM4780 circuit's input configuration.

    James