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Class D Switching Power Amplifiers and Power D/A conversion

Pop-free startup/shutdown
Pop-free startup/shutdown
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Old 25th September 2017, 12:15 PM   #1
robinlawrie is offline robinlawrie  United Kingdom
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Default Pop-free startup/shutdown

Ok im trying to get my head round how to ensure my speakers are safe, using my new diy amp.

Setup is as follows: 2x tpa3255 evm boards, signal from minidsp 2x4HD bare board in same case. All powered by one connex smps 800w psu.

Obviously with one psu and a traditional "kill the mains" power switch, i cannot easily do a startup/shutdown sequence, or use the "reset" jumper on the 3255 boards. How do other people deal with this issue? I cant be dealing with multiple on/off switches and a specific "sequence" its gotta be kid, and powercut proof.

I also need something simple, budget is finished, and there is barely any space left in the box!
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Old 25th September 2017, 12:57 PM   #2
Khron is online now Khron  Finland
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Might something like these help?

Loudspeaker Protection and Muting Figure 3, in the "Muting" section
Project 104 - Preamp/ crossover muting circuit
Power Supply for Preamps The "top" part, with the "AUX" output
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Old 25th September 2017, 01:10 PM   #3
SanjeevM is offline SanjeevM
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The speaker thump at startup occurs bcos the cap bank at zero charge is a short circuit for the trafo and causes a sudden inrush of current.

What you need is a soft start board, which puts a set of resistors in the AC path so that the sudden inrush of current at startup is avoided.

After some time duration, a relay switches the resistors out and direct power goes to the trafo.
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Old 25th September 2017, 01:12 PM   #4
SanjeevM is offline SanjeevM
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Goto the eightaudio.in site and look in the protection modules section. There is a board costing 650 or so.
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Old 25th September 2017, 01:14 PM   #5
robinlawrie is offline robinlawrie  United Kingdom
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Is this also necessary with an smps?

As i understand it, the 3255 has decent dc /short speaker protection,

So i just need the simplest circuit possible which will switch a relay on after a delay, and switch it off as fast as possible on power-off.
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Old 25th September 2017, 01:19 PM   #6
robinlawrie is offline robinlawrie  United Kingdom
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Of course, its possible ill be fine without. Ill be testing when the components arrive.. My gainclone exhibits practically zero noises at start/shutdown.
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Old 25th September 2017, 01:19 PM   #7
Khron is online now Khron  Finland
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I don't suppose you've taken a peek at any of the links i posted, have you?

Granted, if you're using an SMPS to power everything, you might need the smallest transformer you can get your hands on, just enough to power a small relay or two (since the simplest circuits rely on AC detection, and it's not the most "healthy" option to hook them up directly to unisolated mains).
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Old 25th September 2017, 01:25 PM   #8
robinlawrie is offline robinlawrie  United Kingdom
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Sorry, yes i did, its interesting using the ac directly from the switch to trigger fast disconnect of relays. However it seemed that the circuit proposed was drsigned to also provide dc detection and was (possibly?) more complex than what i need.

I guess i should also investigate using a similar circuit to trigger the reset/shutdown function of the 3255, as this would avoid needing high power relays for 6 channels of output. To be honest im surprised this aspect of speaker protection is not automated on these latest-generation chips..
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Old 25th September 2017, 01:28 PM   #9
Khron is online now Khron  Finland
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Hint: the third link i posted (with the added pointer) AC detection is all it does...

Although, as mentioned in my previous post, those circuits are meant to go on the secondary side of a 50Hz transformer.
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Old 25th September 2017, 01:35 PM   #10
robinlawrie is offline robinlawrie  United Kingdom
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Hm possibly i misunderstood, seemed to be an entire psu for a preamp, with an aux. to trigger a mute. . I will study more carefuly.
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