where to put volume potentiometer?

Discussion in 'The Projects Forum' started by paul.1911, Jun 25, 2012.

  1. paul.1911

    Thread Starter Member

    Mar 25, 2012
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    Hello

    I've a small amp to use for small multimedia speakers. I'm using computers 2-3 inch speakers. But the output volume is very high if i'm giving (input) a very little bit volume from the computer.

    I tried 47k stereo volume pot on the output to the speakers but it cant handle :(
    also tried 100k but i'm getting very little effect, 90% turn going blank & at the end volumes up with very little sensitivity. Same is the case with 47k.

    also tried 100k on the input line ... doesn't work :(

    what should i do? please help me how can i reduce the volume?
     
  2. #12

    Expert

    Nov 30, 2010
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    Volume controls are wired up like this.
     
    Last edited: Jun 25, 2012
  3. wayneh

    Expert

    Sep 9, 2010
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    And "output" means from the source, with the "input" becoming the new input to the amplifier.

    A less desirable but still effective approach would be to put resistors in line with the speakers, so that they draw less current from the amplifier.
     
  4. #12

    Expert

    Nov 30, 2010
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    Good point. I was only thinking about the circuit I was drawing, not the circuits paul was thinking about.
     
  5. paul.1911

    Thread Starter Member

    Mar 25, 2012
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    Great idea! :)
    Thanks for the reply
    but can u tell me the value of resistor that i can use?
    I'm not a expert in this :p sorry

    You can see the level of volume i'm giving to my speakers
    [​IMG]

    The speaker impedance is 6 ohms, the amp circuit is may be about 7 watts i think (nowhere printed :( ).

    So which resistance would be fine, so that it can increase the volume on my pc upto 80-90% without a need of a volume pot? and if i want to put volume pot, how much K would be fine?
     
    Last edited: Jun 26, 2012
  6. wayneh

    Expert

    Sep 9, 2010
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    I think the pots you mentioned would be a fine place to start. Just be sure you wire it as shown, and use the wiper as your new "source". The wiper is usually the middle pin, but you should verify that with an ohmmeter. The two outer pins should give you roughly the nominal resistance regardless of where the wiper is.
     
  7. paul.1911

    Thread Starter Member

    Mar 25, 2012
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    You didn't told me the resistance value :(
     
  8. paul.1911

    Thread Starter Member

    Mar 25, 2012
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    I got this link
    http://circuitsdiy.com/6283-audio-amplifier-mostly-used-in-dvdfm

    And the circuit which i bought is very very similar to this...
    This circuit is also working fine in 6vdc
    Ive two circuits to use with 12v 1 amp transformer
    each circuit have inbuilt rectifier with 2200uf capacitor
    single amp is working fine with transformer but after connecting both i'm getting some noise in my speakers...
    I tried everything to overcome with this problem but nothing works
    alas i'm going to try one thing that removing capacitors from both amps
    and going to create my own rectifier to power up both amp circuits
    So i want to know
    If 1000uf capacitor is good to use with rectifier??

    here is what i have made :(
    http://i1133.photobucket.com/albums/m600/paul_1911/Photo0198.jpg
     
    Last edited: Jun 26, 2012
  9. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    No one has mentioned it yet, but there are two different types of potentiometers: linear taper and audio (or logarithmic) taper. Human perception of sound is logarithmic, so the pots used in audio applications are constructed so that "...on a volume control marked 0 to 10, for example, a setting of 5 sounds subjectively half as loud as a setting of 10. ".
     
  10. paul.1911

    Thread Starter Member

    Mar 25, 2012
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    I know but i've asked the shopkeeper to give me the stereo volume controller for my speaker, he gave me 47K... but it start smelling after 5 mins and dead!
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    Hah! Now we understand what you are doing.
    The typical impedance of a loudspeaker is 8Ω.
    Some speakers are 4Ω and even 2Ω speakers are available.

    If you want to control the volume of an 8Ω speaker at the speaker connection you will need a pot about the order of 8 to 25Ω.
    The problem is the pot will have to dissipate all that power.
    Hence if you are delivering 25W to the speaker, the pot will also have to be at least 25W. No wonder you are burning out the pot.

    Why don't you just use the volume control in the Control Panel you posted?
     
    Last edited: Jun 26, 2012
  12. wayneh

    Expert

    Sep 9, 2010
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    You told us you had a 47k stereo pot and a 100k. That's what I was referring to. Maybe the 100k is just a fixed resistor. Your 47k would work fine if it wasn't already destroyed.

    BUT, as shown in post #2, you apply the resistor on the small, line level signals, NOT on the speaker output. The power of the output will destroy the variable pot when it's turned to a low resistance. That turns it into a fuse.
     
  13. Audioguru

    New Member

    Dec 20, 2007
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    A volume control is used at the input of an amplifier. You probably overloaded it at the output.

    Post the power supply schematic showing how many rectifier diodes.
     
  14. dataman19

    Member

    Dec 26, 2009
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    Me thinks he wants a "L-Pad" attenuator.
    ..
    Like audioGuru said - Potentiometers are used at the inputs (where signal levels are relatively low, meaning low power).
    ..
    L-Pats and T-Pad Attenuators are meant for high level/hi-power amp outputs (like the ones feeding the speakers).
    ..
    Dave
    Phoenix, AZ
     
  15. paul.1911

    Thread Starter Member

    Mar 25, 2012
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    0
    No its not 8 its 6 ohms. and the problem is the output to speaker is very high even if i'm giving very little volume (as posted) if i increase it the speaker definitely get damage, therefore, i want to use volume pot, in order to increase volume from the control panel. But where to put? at input or output...thats the main question of this topic.

    Nah..its destroyed. Then i tried 100k pot in place of that and wasn't destroyed, but the effect was very low...i mean 95% of pot turn gone blank and only 5% on the last providing the effect on the volume and i was not able to freely adjust the volume for the speaker..

    as in post #2...i said, i tried that same 100k pot on the input just to check but doesn't work, that wasn't a resistance.

    I tried just to test (because i'm dumb in this stuffs) and doesn't work.

    Sorry don't i've the layout but it is very very similar to this
    http://circuitsdiy.com/6283-audio-amplifier-mostly-used-in-dvdfm

    I think u have put the light on this topic. but i doubt if L-Pats and T-Pad Attenuators are available in my city...
    As wayneh said....why i cant use volume pot on the amp outputs? If resistors would make it work in the input line to the volume pot?
     
  16. Audioguru

    New Member

    Dec 20, 2007
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    A volume control for one channel has 3 terminals. One is from the music source, one is ground and one connects to the input of the amplifier. They must be connected properly for the volume control to work properly.

    If the music source has an output of 0.3V then when it is connected to a 47k volume control the power in the volume control is (0.3V squared/47k)= 0.0000019W which will not destroy the volume control.

    But maybe you connected the volume control to the 7W output of the amplifier and turned down the volume so half the amplifier power went to the speaker and half the amplifier power (3.5W) cooked the volume control.
     
    paul.1911 likes this.
  17. MrChips

    Moderator

    Oct 2, 2009
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    AG has it right:

    1) You blew your pot. You need a new one.

    2) The pot goes at the output of the PC and before the input of the amplifier.

    3) The pot has three connections: output from PC, input to amplifier and GROUND.
     
  18. paul.1911

    Thread Starter Member

    Mar 25, 2012
    33
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    Yeah i know how to connect, i've already checked google before connecting, but the thing is i've connected to amp output and destroyed.
    I'll buy another and try on the input line.
    Anyway,
    Can u tell me if i can reduce the output power from the amp to speakers via resistors? How much omhs would be fine? I want to make the power half.
    I think its 10W because it is very very similar to this circuit.
    http://circuitsdiy.com/6283-audio-amplifier-mostly-used-in-dvdfm
    Its has written nowhere, i've just make a guess of 7W.
     
    Last edited: Jun 27, 2012
  19. Audioguru

    New Member

    Dec 20, 2007
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    If you throw away amplifier power by adding a resistor in series with the speaker then that resistor will get hot and will need to be big enough to dissipate that power.

    The speaker will sound "boomy" (resonate badly) because a speaker depends on the extremely low output impedance of a modern amplifier to damp resonances of the speaker.

    "To make the power half" sounds only slightly lower because our hearing's sensitivity to loudness is logarithmic. 1/10th the power sounds like half the loudness.
     
  20. paul.1911

    Thread Starter Member

    Mar 25, 2012
    33
    0
    @Audioguru
    So is there anyway to reduce the amp output or adding a volume pot on the input line is the only way?
     
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