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(NEED HELP PLEASE!) 1w Amp build

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Justin Verrall, Jun 1, 2018.

  1. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Might be now, but they weren't in your day AG :D

    Plenty of 1M log pots used as volume controls in valve amps.
     
  2. rjenkinsgb

    rjenkinsgb Member

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  3. Justin Verrall

    Justin Verrall Member

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    I did find some on ebay but wouldn't having linear pot defeat the purpose of having an amp to listen to use? I'm guessing there would be no way around the 1m pot either way?
     
  4. dave miyares

    Dave New Member

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  5. unclejed613

    unclejed613 Well-Known Member

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    a 1Meg pot with "A" taper is log taper, so the part would be marked "106A". a linear taper would be a "B" taper, so it would be "106B". whether the pot is used for a control voltage, feedback loop gain set, or input voltage divider, the effect of the log taper is the same, so yes, you want a log taper pot.

    edit: the data sheet says the voltage control has a log characteristic, so you want to use a 1Meg LINEAR ("B") taper pot.
     
    Last edited: Jun 13, 2018
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A linear pot is used and the IC makes it have a log function. It says so in the new datasheet by NXP semi
    ebay sells fake or defective junk. Factory rejects are cheap but work poorly if they do anything.
    1m is 0.001 ohm that you do not want, and 1M is 1 million ohms that you want.
    A volume control allows you to turn up the level to be louder or turn down the level to be not too loud. Without a volume control then you will say, "It is not loud enough, I can't hear it" or "It is way too loud".
    If you are using a volume control on the signal source then the TDA7052A can be permanently set to maximum gain if the 1M pot is replaced with a 1M fixed resistor. The 1μF capacitor also should be parallel to it.
     

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  7. JonSea

    JonSea Well-Known Member

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    There you go with that broad bush again. Sure, some stuff on ebay is junk. But not everything is, nor are all the sellers crooks.

    Buy from known sellers with good ratings and you'll get good stuff. Look for the cheapest parts from a seller that sells mainly non-electronics and you might get screwed.
     
  8. dave miyares

    Dave New Member

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  9. Justin Verrall

    Justin Verrall Member

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    Out of interest would I be able to put a resistor after a 9v battery? Since it's not very common for musicians to use 6v for there pedals.
     
  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A resistor in series with the battery will cause the supply voltage to the Jfet preamp and amplifier IC to jump up and down as you play, causing severe distortion on the loudest sounds.
    The TDA7052A amplifier was designed to use a 6V power supply and drive an 8 ohm speaker but you are overloading it with a 9V battery and a 4 ohm speaker. The overloading will cause it to overheat and it will protect itself by reducing the gain as you play music. Then the volume will suddenly drop then slowly increase over and over.

    Try adding an 8.2 ohm 1W resistor in series with the 4 ohm speaker and use a new 9V battery. The resistor will cause the speaker to sound boomy and muddy on low frequencies and reduce the maximum output power to about only 0.3W.
     
  11. Justin Verrall

    Justin Verrall Member

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    I would be running it through 8 ohm speakers. How will that change the the component needed?
     
  12. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Assuming he was aiming for 12 ohms?, then use a 4 ohm resistor - 3.9 ohm or 4.7 ohm would be fine.
     
  13. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Now you say "8 ohm speakers" which means more than one 8 ohm speaker. Two 8 ohm speakers in series are a load of 16 ohms and the amplifier will be fine with a 9V battery but the total maximum output power will be about 1W which is 0.5W in each speaker.
    Two 8 ohm speakers in parallel are a load of only 4 ohms which will cause the amplifier to overheat unless you add the 8.2 ohm series resistor.
    If the amplifier is driving one 8 ohm speaker and is powered with 9V then add a 3.9 ohm/1W resistor in series with it then the maximum power in the speaker will be about 0.7W.
     

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