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Class D Switching Power Amplifiers and Power D/A conversion

Tripath sleep/mute start up delay
Tripath sleep/mute start up delay
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Old 25th September 2005, 09:29 PM   #1
BWRX is offline BWRX  United States
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Default Tripath sleep/mute start up delay

Note: I posted this over on the 41hz forums, but figured it might get more of a response here.

A lot of people have inquired about incorporating some kind of turn on delay so that you don't hear the loud pop through your speakers when you power up the amp. I know the AMP3 has provisions to incorporate a switch so you can switch the amp between sleep and awake modes. In fact, this is how my AMP3 wired, but even so I still have that turn on pop and the pop sounds the same whether I wake the amp from sleep with the power supply already on or have the amp switched to be awake and simply turn the power supply on. Knowing that, it seems that a small delay to awaken the amp say 1 second after the supply is turned on won't do any good in avoiding the turn on pop. Is there an audible difference between the sleep and mute functions on the chip? Does the mute function have the turn on pop like the sleep function does? I would test this myself but the mute is hardwired to the overload pin and I don't want to ruin my only functional AMP3 at the moment. I'll try it with the sleep pin when I build the next AMP3.

Regardless, I thought up a very simple circuit that could possibly provide the turn on delay.

Click the image to open in full size.

It's just a simple RC circuit with a 1 sec time constant. It can be adjusted higher by using a larger valued cap. I used 1Mohm because the AMP3 is already supplied (at least I think it is) with a 1Mohm resistor for the "sleep circuit". The resistor in parallel is only there to discharge the cap when the amp is turned off - maybe the the PCB connections would already allows the cap to discharge through other components and this resistor would not even be needed. This should work with the sleep pin (not sure about the mute pin) because the Tripath 2021B datasheet shows the sleep pin as a diode followed by a 5V zener internal to the chip. Thus, a logic low won't occur until the cap charges to more than approximately 7V with a 12V supply rail. Actually, now that I think about the big picture, another resistor in series with the capacitor may be needed to limit the current draw through the diodes.

Anyway, just something I was thinking about.
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Old 25th September 2005, 09:45 PM   #2
djQUAN is offline djQUAN  Philippines
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I did incorporate something similar into my amp2 and it works wonderfully. although in my case, I used a few schmitt inverters (the others used for the LED status indicators)

mine mutes the amp at turn on with a delay and at turn off, the amp is muted instantly.
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