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LOUD Subwoofer POP whe powering on speaker  

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Martin
(@martin)
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01/09/2020 6:10 am  

Hi, I've been greatly enjoying my DINAS for the most part of two months now. Last week I added a SABAJ D2 DAC to my setup and I tidied my desk and recabled the s*** out of it. I'm not a big fan of leaving non-vital electronics powered on, so I connected both of the DINAS power supplies to a single power strip with an on/off switch and found out that when powering on the strip a loud POP can be heard (and seen!) from the subwoofers.

It scared the hell out of me the first time it happened as it was an "I might ruin my drivers" loud pop and the subwoofer goes in or out (more on that later) like crazy. I have since then made a series of tests, with the following results:

For a bit of context, my setup goes like this:

Laptop -> USB C HUB -> SABAJ D2 DAC with volume controlled preamp -> RCA out to the DINAS via RCA splitter (sub and satellite volumes at 25%

- At first I thougth the problem was caused by my DAC, as noise can be heard from the speakers if the DAC is connected but not powered, but the pop takes place even if no RCA is connected to the LEPAI amp on the DINAS.

- The pop happens on both speakers, but the cone on the left speaker goes IN whereas the cone on the right speaker goes OUT (i need to check te polarity on both subwoofers just in case I reversed them while finishing the cabinets). Silly me must somehow have reversed the right subwoofer polarity, they're both now reversed and in phase as they should be.

- The loudness of the pop does not vary with changes in the subwoofer volume pot.

- The pop happens when power goes into the amps regardless of being powered on from the amp switch or the power strip.

- It happens in other power outlets in the house and even in a different building.

Is that a normal behaviour for the LEPAI AMP? Is there any way I can troubleshoot the problem more thorougly and (hopefully) fix it?

 

Regards, 

Martin


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TVOR-Ceasar
(@tvor-ceasar)
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01/09/2020 8:58 am  

Sounds like the inrush current charging up the board caps while the speakers are connected. Meaning that there isn't any soft start or speaker protection enabled or included.

Did they do this before, or is this a new development? I can't find any real documentation on the amp board or even a schematic, so this is basically a shot in the dark diagnosis.

 

-Charlie


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Martin
(@martin)
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01/09/2020 9:59 am  

@tvor-ceasar thanks for your answer. I cannot recall them doing that earlier, that's why I hoped for other DINAS owners to chime in just to know if it's a normal thing on these amps.

BTW, the right subwoofer was indeed polarity reversed, so I fixed it during lunch break.


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TVOR-Ceasar
(@tvor-ceasar)
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01/09/2020 1:06 pm  

I looked up the TPA3118D2 Datasheet - the amp chip used.

Page 15, section 7.3.3 should be a clue to what's happening. Directly from the TI PDF linked above:

7.3.3 Startup and Shutdown Operation

The TPA31xxD2 family employs a shutdown mode of operation designed to reduce supply current (Icc) to the absolute minimum level during periods of nonuse for power conservation. The SDZ input terminal should be held high (see specification table for trip point) during normal operation when the amplifier is in use. Pulling SDZ low will put the outputs to mute and the amplifier to enter a low-current state. It is not recommended to leave SDZ unconnected, because amplifier operation would be unpredictable.

For the best power-off pop performance, place the amplifier in the shutdown mode prior to removing the power supply. The gain setting is selected at the end of the start-up cycle. At the end of the start-up cycle, the gain is selected and cannot be changed until the next power-up.

What I'm getting from this is that you should go through a shutdown procedure before unplugging / removing power to avoid "power on pops". If you already do this, then there's something else to figure out.

I'll let other owners chime in for their input and experience.

-Charlie


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Martin
(@martin)
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02/09/2020 10:56 am  

@tvor-ceasar Thank you for your help, I wish my technical english was better so I could extract this precious information from datasheets myself.

If I understood correctly, signal to the amp must be muted before powering off, so the amp itself shuts down its outputs and they remain that way until the next powerup cycle.

I'll have a go and see what I can achieve by powering down the DAC/PRE before powering off the amps.

Again, thank you!


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TVOR-Ceasar
(@tvor-ceasar)
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02/09/2020 11:30 am  

@martin

I'm glad to help if I can. 

From what I read in the Datasheet, the amp itself should go through it's shut down procedure before unplugging / removing power. Since I have never used one, I don't know what that procedure would be. Is there an actual power / standby switch or button on the amp? If so, I would assume (and assuming is never a good thing 😀 ) that would put the amp through the necessary steps to power down correctly.

-Charlie


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ronL
 ronL
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13/09/2020 11:30 am  

@ Martin

If you don't feel comfortable to dig into the TPA3118 board, you might consider a relay with time delay to switch on the connection between the amplifier and the loudspeaker. Many manufacturers use this by the way. If you use the power voltage of the amplifier also to power the relay to switch the loudspeaker, the loudspeaker is than connected to the amplifier after the pop is gone.

Two options that you could use are e.g. a relay with built-in time delay or delay the switching of the relay with a RC network in the coil circuit of the relay. The relay is that fed with the output of the RC, thus is activated with time delay. (Values depending on the resistance of the relay-coil etc.)

This should do the job as wel.


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