4.1 Audio Amplifier

Discussion in 'The Projects Forum' started by Shagon, Sep 3, 2009.

  1. Shagon

    Thread Starter Active Member

    Aug 19, 2009
    48
    0
    Hello i am planning on building a 4.1 audio amplifier is there a way for one potentiometer to control the volume of all the channels? Anyone with experience please lend a hand Thanks...
     
  2. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Use a Digital volume control IC or a 6 channel pot used in entry level home theatres. Some dual pots even have a slot for connection to another pot at the axis. You can try that too if those are available near you.
     
  3. mkbutan

    Senior Member

    Sep 30, 2008
    270
    16
    hi
    i think 4.1 (5) channel potentiometer in not been made up yet
    you can use 2 channels stereo volume controller(2x3=6) yet required r&d in it


    if I'm not wrong then i think you need master volume control after the amp.
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    656
    Perhaps you could use log taper digital pots and control them with a microcontroller.
    Do a search to find more vendors.
     
  5. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    6 channel pots are available. They come as combined form factor of stereo pots x 3 with a common axis extension.
     
  6. Shagon

    Thread Starter Active Member

    Aug 19, 2009
    48
    0

    Well I have done some research and I have seen them but they are digital, which is fine I would settle for that. But if I am to use the digital volume control IC as you stated before do I have to convert the signal from Analogue to Digital?

    And also where is the best place for volume control? before the amp or after the amp? are there advantages and disadvantages?
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    656
    I would think that, if you used a microcontroller, a simple spdt rocker switch could be used to increment or decrement the pot position. A short push would give you one bit of change. Hold it down for more than a second (or whatever), and it increments or decrements until you release it. The only complication is that you would need nonvolatile memory (flash) to remember the volume setting when power is removed.
    There are probably digital volume control ICs available that would make this easier.
     
  8. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    If you are using a dedicated volume control chip, no conversion is necessary, simply feed the line. One such stereo channel chip is DS1669. Stacking 3 of such can also make your volume control.

    Volume controls are placed after the pre-amp and before the power amp. If you have line level inputs, like from a cd player, it first goes to the volume control, then to the amp.
     
  9. Gustav180

    Member

    Aug 25, 2009
    17
    0
    Hello Shagon
    I have just read your problems.

    * You don´t need to convert an analogue signal to a digital when you use a digital pot. Only the control is digital, siganal in and out is still analogue. An other way is to use a LDR + resistor as pot and lamps to control the resistance. This is an old solution from the 60:s.

    * The place for the pot can bee important. The best place is not before because all noice from the amp will bee amplified. In ohter hand it not good to place it after, because there is a high power. Commonly is the place between the pree-amp and the power amp. There is the signal high, about 500 mV and the power is low.

    Best regards
    Gustav
     
  10. Shagon

    Thread Starter Active Member

    Aug 19, 2009
    48
    0

    Ok I never considered the pre-amping part didn't think it was necessary.. is it ok to just use a simple Common Emitter Transistor configuration to pre-amp it and then run it to the Audio IC? Or does that mean I have to get seperate Audio ICs 1 to do the Pre-amping and the other to do the power-amping?
     
  11. Shagon

    Thread Starter Active Member

    Aug 19, 2009
    48
    0
    oh nevermind that question that was a stupid question... I got confused a bit... yes i do intend on pre amplifying it... intend on use Audio ICs to pre-amplify it and then a pnp and npn transistors to power amplify it. so you saying that the volume control would work best after the audio IC?
     
  12. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Dont do a pre-amp if its a line level input. It will give a distorted and clipped output.

    Pre-amping is only necessary for mic level, cassette head level and extremely weak signals after a long stereo cable. Otherwise it should not be used.

    If you have a CD or computer output, connect it direct to the digital volume control chips and then directly to the power amp. A noise filter is also good.
     
  13. Shagon

    Thread Starter Active Member

    Aug 19, 2009
    48
    0
    Ok Next question I wanna filter out 4 channels each channel would have a mid and treble out put and I wanna control the volume for both mid and treble seperately.

    Filter normally occures after amplification right? since i want a volume for both mid and treble seperately that would mean that I would have a volume control after amplification would that be ok?

    Lol I hope you guys understand my question I can't really explain things well...
     
  14. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    I think what you are asking is a bass/treble control. You can get a pair of stereo B-T boards and wire it up. Or just google for 'tone control circuit' or 'bass treble circuit'. You can also build one using the TDA1524 stereo tone control IC. Two stereo boards will be necessary for 4 channel. The easy way is to buy one. All of them have individual bass/treble knobs for what you call 'bass and treble volume control'. Some also have built in volume control.

    First supply the line level signal from your source to the tone control circuit, then volume control and then amplifier. All audio processing circuits are always used on line level as it works best there. Nothing should be connected between the amplifier and speaker except capacitor filters and audio crossover networks.

    Filters occur after amplification only in cross over networks to seperate bass, mid-range and high frquencies to their respective speakers. They are passive.

    You can connect the volume control first and then tone control, but that will not be as effective as the first way.The best way is.

    From Pre-amp or CD ===>> Tone control ==> Volume control ==> Power Amplifier.
     
  15. Shagon

    Thread Starter Active Member

    Aug 19, 2009
    48
    0
    Ok help me out here a little tell me if I am wrong or not..... This is my very very first project.... I know what tone controlling is.... And I thought of well it might sound crazy that instead of actually implementing tone controlling I would have the amplifier output both a high frequency signal and a midrange signal per channel.... One two a Mid range speaker and the other to a twitter speaker....

    Now what I was thinking is that.... Lets say I want only high frequency sound I would low down the volume to the mid range speaker and increase the volume to the twitter speaker... Like wise if I want mid range frequency sound I would low down the volume of the twitter speaker and increase the volume of the mid range speaker... or if i want it in between I would ajust the volumes until I get a sound that I want... That way sounds would blend with each other and it would SOUND like I am doing tone control....

    Please tell me your Views on that... I know I can be crazy sometimes... well all the times...
     
  16. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    What you said can be achieved using a tone control board and 4 channels. You can adjust the bass and the midrange speakers will respond accordingly whereas the tweeter will have only a minimum response to midrange frequencies and vice versa. Such a setup will have both the midrange and tweeter in the same speaker box connected in parallel with the tweeter connected in series with a 1uF capacitor as a filter. This is the common setup used in HT's.

    Input ==> Tone control ==> Volume ==> Amp ==> Midrange speaker ==> filter capacitor ==> tweeter


    But from what you wrote, I think you needed a more complex setup, using seperate channels for the tweeter and midrange. That is rarely used cos it is a studio setup and is costly as you will need 8-channels to get a 4-channel output. 4 channels for midrange and 4 channels for high frequency. I don't think you will be looking at that. It is done by
    Input ==> band pass filter ==> Volume ==> Amplifier ==> mid-range speaker
    Input ==> hi-pass filter ==> Volume ==> Amplifier ==> Tweeter

    Is this what you are asking for?? A good tone control about 70% can be obtained using the first method I described, though not as perfect as the second one.
     
  17. Shagon

    Thread Starter Active Member

    Aug 19, 2009
    48
    0
    Lol lol The reason why I came up with this idea is because when I thought about adding in a tone control to my amplifier i was thinking of a way in which to implement it. Then I got lazy and I thought that it would actually be easier to just adjust the volume of a midrange speaker and the twitter speaker and actually thought that that would give me better tone control.

    I thought it was easier because I was just gonna connect the mid range speaker and the twitter speaker in parrallel like you stated coming from a channel and filter them out using a band pass filter and a high pass filter and just add in a potentio metter to ajust the volume simple...

    but like you guys stated its not wise to place a volume control after amplificaton.
     
Loading...