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8 (7.1) channel analog volume control

Discussion in 'General Electronics Discussion' started by CommanderLake, Oct 2, 2012.

  1. CommanderLake

    CommanderLake

    193
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    Oct 2, 2012
    First I would like to point out this amazing java circuit simulator: falstad.com/circuit

    I've been looking for an affordable way to apply analog volume control to a 7.1 audio source using a single knob with no success, does anyone have a solution?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Presumably it is an existing device. Possibly it has digital circuitry prior to the amplifiers. Potentially that has a single control for level.

    Find out what device (if any) is in use and how the output level is set. Then maybe there will be a way to change this with just one knob.
     
  3. CommanderLake

    CommanderLake

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    6
    Oct 2, 2012
    Sorry I didn't give enough detail, Its the output from my X-FI, I want to replace my old Gigaworks s750 and theres no way I'm handing main volume control of a 50+ watt (depending what the new amp will be, possibly ebay item no. 200723854869) 7.1 system over to software because the volume can change itself when changing modes etc. and digital volume attenuation results in loss of dynamic range and a much higher noise floor.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I'll repeat:

    Presumably it is an existing device. Possibly it has digital circuitry prior to the amplifiers. Potentially that has a single control for level.

    Find out what device (if any) is in use and how the output level is set. Then maybe there will be a way to change this with just one knob.
     
  5. CommanderLake

    CommanderLake

    193
    6
    Oct 2, 2012
    Sorry I cant solve your riddle.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, tell us what the manufacturer and model number of your amplifier is.

    Describe the connections from your signal source to the amplifier (is it a single digital link)?
     
  7. CommanderLake

    CommanderLake

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    Oct 2, 2012
    I might use this as the amplifier: ebay item 200723854869
    The thread title does say analog, standard line level.
    I can make the connections whatever I like, RCA connectors seem the likely choice so 8 RCA connections at line level with bare wire from preamp to amp.
     
    Last edited: Oct 2, 2012
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Does your preamp have a volume control? (that's normally where they are).

    What make and model is it, and is it's input digital?

    Oh, and that amplifier has a significant number of surface mount components -- can you solder them?

    I've checked the chip used on this board and it doesn't have any gain setting that can be paralleled.

    The other alternative (if nothing has a gain control yo can use) is to get a digital pot chip and use a series of them driven from a single signal to control gain.
     
  9. CommanderLake

    CommanderLake

    193
    6
    Oct 2, 2012
    A preamp with a volume control is exactly what I'm trying to make to go between sound card and amplifier, I have done plenty of thru hole soldering but no surface mount but it says in the description that the seller will solder it for me if I pay extra.

    I came here to ask if there is any circuit I can use to apply preamp volume control to 8 channels at once without an 8 gang pot which I just cant find.
     
    Last edited: Oct 2, 2012
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, so no preamp and you don't own the amplifier either yet. And you're going analog out from your sound card (8 x RCA plugs or similar?)

    You could use a chip like this for each channel, and a microcontroller to drive them. It wouldn't be trivial.

    There are simpler circuits based on jfets used as variable resistances, however they can have some pretty dreadful distortion. Here is a circuit that limits the voltage across the jfets to get good performance. You'd have to build 8 of these but the control voltage could come from a single source (although you'd have to be careful of introducing crosstalk).
     
  11. CommanderLake

    CommanderLake

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    Oct 2, 2012
    I had a good look at this a couple days ago: CS3308/18
    but the task of incorporating it into my own design seems a bit daunting I'm still a rookie with Diptrace.
    I know what you mean about the J-FET's you can visualize it with this simple circuit I just made using the Falstad circuit simulator java applet use the "Voltage" slider on the right to change the gate input voltage, if the gate voltage goes too low you get a reverse bias and the simulator stops just raise the voltage again and the click "Reset" button top right.
    J-FET resistor circuit
     
    Last edited: Oct 2, 2012
  12. CommanderLake

    CommanderLake

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    Oct 2, 2012
    Do you think the CS3308 would be of use in my application? If so I could use a circuit diagram to help me get started.
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The datasheet contains all the information you need.

    If you've never soldered surface mount components then this chip may not be the one for you.
     
  14. CommanderLake

    CommanderLake

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    Oct 2, 2012
    I have watched lots of educational videos on youtube I might be able to manage it, maybe theres a cheap SMD kit I can practice on
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You could start by building that amplifier yourself. Although it may be better to start on something simpler. Have you soldered through-hole components?

    Even after that, you're going to have to design and make (or get manufactured) a printed circuit board.
     
  16. CommanderLake

    CommanderLake

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    Oct 2, 2012
    We all have to start somewhere and yea I have done a few Velleman kits including the K4004B, K4006, K8084 and a few K1823's.
     
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Cool. You have some experience.

    I'd recommend trying to find a DIL chip that maybe has less channels, but will be easier to breadboard a solution. You may even be able to get away with veroboard construction.
     
  18. CommanderLake

    CommanderLake

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    6
    Oct 2, 2012
    There's only stereo PDIP chips so I would need 4 of either PGA2310 or PGA2311, the 2310 has a wider input voltage range at the cost of slightly more distortion.
    Then I need a micro controller and a PIC programmer such as the Velleman K8048, the programming shouldn't be a problem that's another hobby of mine, then I need a physical means of controlling the volume.
     
    Last edited: Oct 3, 2012
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It might be worth looking at something like a PicAxe because you can save yourself a programmer and the code will be rather more trivial to write.

    edit: or even an Arduino, but the cost of that is probably not worth it.
     
  20. CommanderLake

    CommanderLake

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    Oct 2, 2012
    PicAxe looks great what size do you think I need?
     
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