Amplifier mute control

Discussion in 'The Projects Forum' started by Fenris, Aug 14, 2009.

  1. Fenris

    Thread Starter Active Member

    Oct 21, 2007
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    Hi Guys

    Right then my latest weird and wacky circuit involves the control of a the mute function on an AN5279 Amplifier chip. The amplifier circuit itself is very simple requiring only a minimum of parts to get it running.

    This project will run on 12VDC.

    2 pins of the chip require 5V as a control voltage. The standby pin needs 5V +VE for the amplifier to be 'ON' A simple resistor potential divider will be used to attain this .

    Now the mute pin responds to 2 states or inputs. +VE 5V will mute the output. 0V will un mute the output.

    My intention is to use a 7555 timer circuit to control the speed at which this mute happens. I am not looking to turn the mute on and then off when I want this is a permanent cycle running at whatever speed I set the timer to run at.

    Now the bit where I lose it is the actual joining of the 7555 output to the mute control. I believe I need a transistor driven by the 7555. The collector goes to +VE supply with 2 resistors in line to form the resistor potential divider for the 5V needed to control the mute.

    So when the transistor is off the mute pin gets the +VE 5V so the chip is muted. When the transistor receives a signal from the 7555 it opens and the mute pin is taken to 0V or GND.

    I attach a diagram of my intention. Have I got it right as far as the interface of the 7555 to the mute pin is concerned?

    regards

    Fenris
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    In your schematic the mute input will be VCC or the voltage of the divider.

    Here I have made a little change.

    [​IMG]

    The transistor will pull down the mute input.

    Greetings,
    Bertus
     
    • Mute.jpg
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  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    You also need base current limiting for your transistor. See attachment.
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Good catch Ron.
    Without the base resistor the transistor will not survive.

    Greetings,
    Bertus
     
  5. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi Guys

    Thanks for the input. I am just breadboarding the amplifier on it's own to check it is working. The I have a 556 chip setup from a prior experiment so I will integrate that as soon as I know alls well.

    regards

    Fenris
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    There will be some delay in the reaction time for the mute.
    There are a resistor of 8K2 and a capacitor of 10 μF at the mute input.

    Greetings,
    Bertus
     
  7. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Thanks Bertus. That will need addressing as well then. But for now neither the AN5279 or the AN5276 show any sign of life. Iam checking my wiring but so far nothing obvious is amiss. Ho Hummmmmmm!

    regards

    Fenris
     
  8. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi chaps

    I can't believe that all the chips are duff. Here is the data sheet page for the AN5279. It shows how to connect it up. I had a potential divider network to set the 5V needed to ensure that the standby was off so the amp was running. The mute was taken straight to GND so that the mute was off. the IN GND and OUT GND were seperate from the supply GND and each other.

    Have I missed something? Or is there more to it than the seemingly simple diagram The Supply was 12VDC.
     
  9. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Actually, the mute ON time constant is ((15k||20k)+8.2k)*10uF=168mS. The mute OFF time constant is 82mS.
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    See the explanation below.
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    With a 12V supply the output of the Japanese IC at clipping into an 8 ohm speaker is only 1.5W. Is that enough power?
     
  12. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi chaps

    Thanks for the input. I will try again today with the chip.

    AudioGuru, Not really but this is primarily a test to see if the idea of controlling the mute control as I intend is feasible. If it works as I hope then I will be on the hunt for a 12V chip with at least 5W or one that can be BTL'd with itself for greater output.

    regards

    Fenris
     
  13. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi Chaps

    Well it does live! Thanks Ron for pointing out what, to me, was a bit confusing. I will now attempt to fire up the timer control and see where we go from there :D

    regards

    Fenris
     
  14. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi Chaps. I need your help on this final part of the puzzle. I have setup the mute control as in the diagram that Ron corrected for me. But the amp doesn't mute under the control of the 555/2N3904 control. Any hints?
     
  15. bertus

    Administrator

    Apr 5, 2008
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  16. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You did remove the mute switch?
    Did you adjust the 8k2 and 10 μF?

    Greetings,
    Bertus
     
  17. Fenris

    Thread Starter Active Member

    Oct 21, 2007
    288
    2
    Hi Bertus

    There is no physical switch. I am trying to control the mute function purely with the transistor if possible. I even bypassed the mute timing components and made the 555 timer very slow to see if that helped.

    It seems very simple to do. 0V and the amp is active. pull the fly wire and it stops IE floating..............A thought occurs to me.........Im using a NPN transistor would a PNP be a better option?

    regards

    Fenris
     
  18. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Does the voltage on the collector of the transistor react on the pulses from the NE555?
    If not lower the base resistor a bit.

    Greetings,
    Bertus
     
  19. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have looked at the datasheet.
    The transistor can be ommitted.
    The NE555 when powerd at + 5 Volts will drive the mute directly.

    [​IMG]

    Greetings,
    Bertus
     
  20. Audioguru

    New Member

    Dec 20, 2007
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    An NE555 is an ordinary 555 and is completely different to the Cmos ICM7555 that you should use. An LMC555 and a TLC555 are the same as an ICM7555.
     
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