Audio Volume control

Discussion in 'The Projects Forum' started by FrozenMel, Oct 6, 2011.

  1. FrozenMel

    Thread Starter Member

    Aug 23, 2011
    34
    0
    Hey,

    I am trying to control the output volume from a 70V constant voltage audio system using a digital pot but I cannot find a pot that I think will work for such high voltage.

    I also don't really understand the 70V constant voltage speaker system signals. Is the output 0V-70V? Is the output differential around 35V or 0V? If anyone has a graph of what the output looks like that would be amazing.

    I'm pretty sure the output of my audio amplifier will not go beyond 10W but if possible, I would like to find a digital pot that can handle up to 35W. Do digital pots exist for such high power or is there a way to setup a normal digi pot to handle the signal but still allow for a full range of volume control?

    If possible, I would like to use SPI to control the pot.

    Thanks in advance.
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    No, there is no digital pot that can handle high power. They all are designed for low level signals ( with peak voltage generally limited to the DC supply voltage or less).

    Normally, you control the input of an audio amp to change the volume, not the output. If you need to control the output, then you can use an audio autotransformer such as this. Using a pot wastes a lot of power.

    There's nothing unusual about a 70V audio signal except for the voltage and impedance level. A 70V audio system is designed to have an audio output of 70VAC at the nominal output power. Transformers with taps for the desired speaker power level are then used at each speaker to reduce this to the lower voltage required by the speakers.
     
  3. FrozenMel

    Thread Starter Member

    Aug 23, 2011
    34
    0
    Yeah, I am using a Bogen AT10A which is basically the same on the far end near the speakers.

    But what I want to do is be able to control the volume through programming so I could say...hook up a micro and adjust the volume through IP. This way I can set the maximum volume say...on 15 different speakers at home while at work. I physically can't use a bunch of manual knobs to adjust the volume due to space requirements and project needs.

    If there was one of the audio autotransformers that had a program adjustable level that would work. Like one that had some sort of servo that turned the knob based on some serial input. It would have to be relatively small though and nowhere near the size of the wall mounts.
     
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