What's the absolute best opamp for audio purposes?

Discussion in 'General Electronics Chat' started by zero_coke, Dec 3, 2011.

  1. zero_coke

    zero_coke Thread Starter Active Member

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    I want to build my own amplifier for home and I want to use top-of-the-line stuff...what is the best opamp and transistors I should use? I will be using +/- 15V DC power supply for my amplifier, and my speakers are 60W, 4Ohm speakers.
  2. Audioguru

    Audioguru New Member

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    With a 30V supply and a single-ended amplifier circuit the power into 4 ohms is only 13.8W. Maybe your speakers are rated at 60W peak which is 30W RMS.

    An OPA134 single, OPA2134 dual or OPA4134 quad opamp is excellent. The max allowed supply is 36V.
  3. zero_coke

    zero_coke Thread Starter Active Member

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    That MC34071 you recommended to me was not functioning well...:( I went out and bought the NE5532AP and the NE5532AP had way less distortion and better sound quality...and that input coupling you showed me didn't work...when I put those capacitors at the input my entire circuit didn't function for some reason ....I attached the image you showed me. What I did instead was I grounded the Vcc and Vee of my opamps through a capacitor and it worked like a miracle...all the noise suddenly disappeared!!! It was such a drastic and significant change...I didn't know Vcc needed AC coupling capacitors to block the AC induced into the DC power supply....

    Oh and I want to make stereo amplifier so I want to build two amps but I only want to use 1 DC power supply. I heard you can offset the opamps so that you can get away with using one Vcc instead of two (Vcc and Vee). How can I do this?

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  4. jimkeith

    jimkeith Active Member

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    You may wish to go with a bridge type output as it doubles the output voltage and multiplies the power by a factor of 4.
  5. zero_coke

    zero_coke Thread Starter Active Member

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    What's a bridge type output??
  6. nsaspook

    nsaspook Senior Member

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  7. zero_coke

    zero_coke Thread Starter Active Member

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    Ugh...I did some googling and I can't decide between these...I've never used any and I don't know which one is the best

    OPA627
    TL072
    AD8610
    AD829
    AD8033
    OPA2134
  8. nsaspook

    nsaspook Senior Member

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    Anything from Texas is the best. ;)
  9. jimkeith

    jimkeith Active Member

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    audioguru suggested this bridge output IC in a previous thread--he can probably suggest some others as well as I am not expert here.
    http://forum.allaboutcircuits.com/showthread.php?t=51750&highlight=bridge output amplifier

    What the bridge amp does is to drive both ends of the speaker coil, instead of working against common (ground) as most amplifiers do. While one side is increasing in voltage, the other side is decreasing by the same amount in the negative direction.
  10. zero_coke

    zero_coke Thread Starter Active Member

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    So which one of these is the best guys?

    OPA627
    OPA637
    TL072
    AD8610
    AD829
    AD8033
    AD8620
    OPA2134

    Price is not a concern (since I'm only going to buy 4).
  11. jimkeith

    jimkeith Active Member

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    What kills audio quality in op amps is called crossover distortion--this occurs at mid-voltage when the current output changes directions (different output transistors are switched on). It tends to be a fixed level of distortion voltage--not very noticeable at rail to rail output, but very noticeable at low signal levels. This is a problem in cheap op amps like the LM324 that are not really intended for audio.

    I honestly do not know what to look for in the specs to avoid this--the experience of others here is vital in op amp selection--also there are really a large number of suitable devices.
  12. nsaspook

    nsaspook Senior Member

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    Spec wise best:
    Burr-Brown OPA627

    Complete Overkill for audio.
  13. zero_coke

    zero_coke Thread Starter Active Member

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    Thanks nsaspook :)

    Ah damnit...see the thing is, the other opamp you showed me was titled "High Definition Audio OpAmp" while this one is named "Precision High Speed" opamp...now I'm in the same dilemna again...do I pick the audio opamp or the best spec one?
  14. jimkeith

    jimkeith Active Member

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    I'd go with the one designed for audio.
  15. Audioguru

    Audioguru New Member

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    The input of the opamp should be at half the supply voltage which is ground with a dual polarity supply. If you use a single polarity supply then use two resistors and a filter capacitor to make a voltage divider that provides half the supply voltage. The output will also be at half the supply voltage so a coupling capacitor must feed the speaker.

    The TL072 and the OPA2134 are dual opamps (two opamps in 1 package). I didn't look at the others.

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  16. zero_coke

    zero_coke Thread Starter Active Member

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    I don't get it...how will the opamp work if I just ground the Vee then? Are you saying that I should feed the non-inverting input of opamp with half the DC power supply and the other half to the Vcc??
  17. Audioguru

    Audioguru New Member

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    Look at my previous schematic:
    1) Connect Vee to ground.
    2) Vcc is the positive supply voltage like before.
    3) Make a voltage divider to provide half the supply voltage to the non-inverting input of the opamp.
    4) Add a coupling capacitor to drive the speaker.
  18. zero_coke

    zero_coke Thread Starter Active Member

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    I don't understand the coupling capacitor part...where do I put my speaker? Plus, this opamp stage is only my voltage gain stage...the output of this opamp is going to a class AB amplifier, so do I place the output of the class AB amplifier in parallel with a capacitor??
  19. nsaspook

    nsaspook Senior Member

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  20. Audioguru

    Audioguru New Member

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    With a single polarity supply the non-inverting input of the opamp is biased at half the supply voltage which makes its output at half the supply voltage so it can swing equally up and down. Then the output of the class-AB output stage is also at half the supply voltage. If you connect a speaker directly to the output and to ground then it will pass a high DC current all the time which pulls the speaker cone to one side and heats the speaker and the upper output transistor.
    The speaker works with AC not DC so add a coupling capacitor in series with the speaker to block the DC from the output of the amplifier but pass the AC signal to the speaker.
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