Tl072 preamp and TDA2050 amp

Discussion in 'The Projects Forum' started by Injac, Jul 22, 2017.

  1. Injac

    Thread Starter New Member

    Jul 22, 2017
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    Hello, i lets say "designed" this circuit, just took parts from other projcets, datasheets, and kinda mixed it all in to create one pre-amp with TL072 and an amp with TDA2050. I have speakers that are about 20W each channel. I dont need any bass balance, treble etc in the circuit, i just want to amplify the signal from the input so i get on the output around 20V. The crossovers i will do in the speaker box. Used P1 as the balance between left and right channel, and P2,P3 for the volume control. My question is, will this circuit work, since its my first project of this kind, im sure i have some major failures in the design, would someone look up the circuit and modify it if needed so it would work good. I dont need it to maximum perfection, just so it doesnt have large distortions and it will do its job. I just want to make a small Hi Fi. Thank you in advance :)
     
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  2. OBW0549

    Distinguished Member

    Mar 2, 2015
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    Polarity of C6, C13 and C21 is shown incorrectly.
     
  3. Injac

    Thread Starter New Member

    Jul 22, 2017
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    Thank you didnt notice it, otherwise the general amplification its good? Will work?
     
  4. OBW0549

    Distinguished Member

    Mar 2, 2015
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    I can't tell for sure without doing a lot of reading and calculating, but I didn't see any obvious, glaring flaws.

    However, I question your choice of R9 & C15, and R15 & C17; these components comprise a pair of low-pass filters on your inputs with their -3 db point at 340 Hz. That seems rather low for an audio amplifier. If it were me, I'd make C15 and C17 something like 2.2 nF rather than 100 nF.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    I believe you mean 2.2μF. ;)
     
  6. OBW0549

    Distinguished Member

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    Absolutely not.

    Look again at what those capacitors are doing: along with R9 and R15, they form low-pass filters that determine the upper end of the amplifier's frequency response. For audio work, a corner frequency of 340 Hz is way too low, so the capacitors should be made smaller.
     
  7. crutschow

    Expert

    Mar 14, 2008
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    Of course.
    Somehow I was thinking they were series coupling capacitors. :oops:
     
  8. Injac

    Thread Starter New Member

    Jul 22, 2017
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    These are the circuits i was looking at from which i put them together, so on some i see the same values and i see its also a low pass filter but its also in datasheet of TDA 2050? So from these circuits how would you combine it and change in it? Thank you
     
  9. OBW0549

    Distinguished Member

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    Actually, I would go with the circuit you originally showed us, plus the modifications that have been suggested. I think the resulting circuit would work quite well.
     
  10. Injac

    Thread Starter New Member

    Jul 22, 2017
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    Ok so here are with all the modifications, i calculated the filters low/high pass etc, its all in range between ~7Hz to 22kHz, now the only thing if you can check are those values good i mean i have 1.5nF and a 4k7 resistor at the input of preamp, should i maybe reduce the value of the resistor and increase the value of capacitor is 1.5nF too low? If you know what i mean, theoreticly i know that the values are best when they are kinda in the middle so the resistor is not to high and capacitor too low and the other way around. If you understand what i said :D

    My other question is also if this is the final circuit. What kind of capacitors should i use for which part of the circuit i know from the supply like C3, C6, C10, C13, C19 and C21 i should use electrolit, but for the others im not sure, should i go for electrolit, block, mayler, ceramic etc. And what to those kind of capacitors bring to this circuit, what changes when they are diffrent kind (just for my knowledge in the future). Im very thankful for you patience and help. Thank you once again :)
     
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  11. MrChips

    Moderator

    Oct 2, 2009
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    You don't need R14 and R20,

    (As a hint, when laying out a circuit with duplicated sections, use part identifiers such as R114 and R214 to make it easier to recognize the same component in different channels.)
     
  12. Injac

    Thread Starter New Member

    Jul 22, 2017
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    Ye will do that so i get a better recognition, besides the R14 and R20 would you change something else? Thank you
     
  13. OBW0549

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    The 47 uF capacitors are aluminum electrolytics. The 100 nF capacitors are ceramic, as are the 1.5 nF. The remaining capacitors should be mylar, or can be ceramic although there might be some distortion issues.

    As for capacitors and their characteristics, the attached files should help.
     
  14. Injac

    Thread Starter New Member

    Jul 22, 2017
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    Thank you very much, distortions will happend when with ceramic instead of mylar or you are generaly speaking?
     
  15. MrChips

    Moderator

    Oct 2, 2009
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    For R4 and C5, why are you deviating from what is recommended in the manufacturers data sheet?
     
  16. Injac

    Thread Starter New Member

    Jul 22, 2017
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    Yeah you are right, i changed that R4 and C5 and R8 and C12. Thank you
     
  17. Injac

    Thread Starter New Member

    Jul 22, 2017
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    Just did a test run, and the sound is horrible, alot of distorsions :/
     
  18. crutschow

    Expert

    Mar 14, 2008
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    Sounds like something is not biased properly and you are getting clipping.
    Do you have access to an oscilloscope?
     
  19. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The input opamps are DC coupled.
    Perhaps there is some DC on the input signal that will have the opamp to clip.
    Put a capacitor in series with the inputs.

    Bertus
     
  20. Injac

    Thread Starter New Member

    Jul 22, 2017
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    Ye a friend told me to put a 1uF, i did that before that i didnt even get a signal, sry no im at home, just have a multimeter, dont have an osciliscope, what else could i try?
     
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