Electronics > Projects, Designs, and Technical Stuff

Speaker POP in class-d system design

(1/3) > >>

SpiderElectronics:
Hi
I have designed a 20+20W audio amp based around the Texas TPA3123D2http://www.ti.com/lit/ds/slos541c/slos541c.pdf Class D amplifier chip.
The chip has logic inputs for MUTE and SHUTDOWN.

If I connect the speakers with relatively short cables - say 1 or 2 metres, then the thing works beautifully. However, if I use long (say 20m) cables then there is an annoying POP when the chip comes out of SHUTDOWN.

I have tried keeping the MUTE asserted until a while after the SHUTDOWN is removed, but that makes no difference - mainly because in this CLASS-D design the 'Mute' control actually just puts the switching push pull mosfets into a 50-50 duty cycle rather than turning them off.


Can anyone suggest why this should be, or have any ideas for a way to get rid of the POP?

Lightages:
Really? 20 metres? That is a very long run. The problem with such long runs of speaker wire is that you can end up having a very reactive load in the cables. This reactance is probably causing your "pop".  What gauge wire are you using? For 20 metres it should be no less than 10 gauge I would think.

chscholz:
Not my field of expertise by a long-shot.
It appears to me as is some folks filter pops out in DSP. I helped customers on occasions to build math functions on a LeCroy WaverRunner oscilloscope that implements an A-Weighted filter. Such filter, as I understand it, do just that, filter out pops.



--- Quote from: SpiderElectronics on April 17, 2012, 11:02:38 pm ---Hi
I have designed a 20+20W audio amp based around the Texas TPA3123D2http://www.ti.com/lit/ds/slos541c/slos541c.pdf Class D amplifier chip.
The chip has logic inputs for MUTE and SHUTDOWN.

If I connect the speakers with relatively short cables - say 1 or 2 metres, then the thing works beautifully. However, if I use long (say 20m) cables then there is an annoying POP when the chip comes out of SHUTDOWN.

I have tried keeping the MUTE asserted until a while after the SHUTDOWN is removed, but that makes no difference - mainly because in this CLASS-D design the 'Mute' control actually just puts the switching push pull mosfets into a 50-50 duty cycle rather than turning them off.


Can anyone suggest why this should be, or have any ideas for a way to get rid of the POP?

--- End quote ---

SpiderElectronics:
Thanks for the replies.

For the cable gauge - I'm not sure - this report came from an installer - but I have asked him the gauge of cable being used.
As for DSP, well there is no DSP anywhere in this system and it happens when asserting/removing the SHUTDOWN signal to the amp.

The cables runs are long because the main unit goes in a closet and gets wired out to the whole house. It is a multi source/multi room system making a 4 x 4 matrix.

amyk:
Curious how the datasheet says

"Advanced Power-Off Pop Reduction"

and

"The patented start-up and shut-down sequences minimize pop noise in the speakers without additional circuitry"

Have you tried measuring the outputs with a scope when turning on, both at the amp outputs and at the speakers? How about slowly ramping up the supply voltage when turning on?

Navigation

[0] Message Index

[#] Next page