need help supplying proper amp mute pin voltage

Discussion in 'The Projects Forum' started by mcd, Oct 10, 2007.

  1. mcd

    Thread Starter New Member

    Oct 10, 2007
    Hi all,

    I'm working on my first project, to build a replacement controller for a set of Monsoon Planar Media 9 speakers. So, there's a bit of a crash-course in electronics happening as well. I'm having a little trouble understanding what I need to supply on one of the controller pins to the mute switch circuit that's on the main board.

    The unit uses a TDA8567Q amp. The datasheet at shows the mute circuit on page 5. I've looked up the datasheets for all the components, but I'm still a bit lost to explain what all is happening.

    I fried the NEC DS882 on the main board that supplies 9V to the controller port hoping that I could simply connect the mute pin wire, 9V+ and GND (yes, probably not the best way to experiment). I'll be replacing the 2SD882 with an NTE184 soon.

    The original controller (I don't have one) contains an active crossover for the sub, volume pots, and a mute button with LED. I'm using a Pyramid car crossover on a separate 12V power supply (maybe version 2 of the controller will include a DIY crossover).

    I would greatly appreciate some help in understanding how the mute circuit works, and what I need to do in the controller to trigger mute mode (3.3-6.5V @ 30-80uA) and operational mode (>8.5V @ 30-80uA) on the amp. Specifically, some of the questions I'm stuck wondering are:

    1. I assume the capacitor plays some role in the amp's recommended 18V/s slope when moving from standby to mute mode, is this accurate? I also don't know how to visualize the effect the capacitor has on the zener. I assume the 3.9V zener must be there to regulate the voltage for mute mode.

    2. I'm also having trouble visualizing the effect of the reverse bias diode across the resistor and would like to understand its purpose.

    Thanks very much for any help!!!

    Best regards
  2. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    If you connect a switch PROPERLY, between 9V and GND, just as shown in the datasheet, it should work.

    However, it may be necessary to isolate your switch from other circuitry.

    You may need to lift both the 10K and diode cathode at that junction, resolder the parts together off the board, and then run to your mute switch.

    Or, cut any trace that goes from the junction of those two parts to other circuitry.
  3. mcd

    Thread Starter New Member

    Oct 10, 2007
    Thanks a lot for the response. After some more thought, I think I understand the flow of electricity a lot better. I'm assuming that the zener diode effectively changes the ground voltage to 3.9, so while the capacitor is charging, it provides a sloping 5.1V to the mute pin in the IC, right? And when the capacitor is fully charged, the IC will get 9v in series with the 10k resistor. I was a bit confused by the datasheet stating that the operational mute pin current would be 70uA. I didn't understand whether this meant that you had to somehow limit current before the pin, or that there was an internal resistance in the IC handling this current.

    It seems like the mute circuitry then, just provides a smooth transition from standby to operational and vice versa, without actually providing a way to stay in mute mode continuously at 5V.

    And thanks for putting up with my beginner questions!