(Topic ID: 296173)

Speaker Protection Circuit: How to Change Delay time?

By rockwell

3 months ago



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  • 6 posts
  • 2 Pinsiders participating
  • Latest reply 3 months ago by rockwell
  • Topic is favorited by 1 Pinsider

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#1 3 months ago

I am adding a speaker protection circuit board to my NBAFB to eliminate the speaker pop on startup/shutdown. It works, but the delay isn't quite long enough to cover all of the pops. Does anyone know how I might make the delay longer? I don't know enough about it to know if swapping out component values would achieve this.

Any thoughts? I appreciate the help.

The board I'm using:

PXL_20210703_173953915-1 (resized).jpg
PXL_20210703_174004990 (resized).jpg

#2 3 months ago

Bump and update. Cheers!

#3 3 months ago

Pin 7 of the 1237 determines the turn on delay.
Default value per data sheet is 33uF and 56K ohms.
C2 on your board = 47uF, Resistor (far left resistor on your board) = 56K.
So they appear to be going a little longer than default delay.
It's difficult to calculate the actual turn on time since this board is operated at voltages lower than the recommended operating supply voltage (25V).

Usually this is an RC time constant for determining turn on time. Increase the value of the capacitor C2 to increase the time delay - maybe to a 56uF or 68uF and see what happens (56 & 68 are not popular and tend to be harder values to find).
You want a decent cap there. Any brand electrolytic will decrease in value as they age. As board gets older, the pop will gradually return until that cap is changed -- but this could take several years to reappear. Interestingly, they used three electrolytics on this board -- two piece of crap Lelons and one Nichicon UVR cap (decent cap). They used the better grade of Nichicon for the time constant. A Nichicon UVX type cap may be a better choice -- UVX is a higher temp rated cap which tends to have better seals/electrolyte and may last longer.

#4 3 months ago

Thanks, Ed. Appreciate your knowledge, as always. I'm gonna hunt down a slightly higher value cap for C2 as you mentioned, and might as well swap out those other two for better quality ones as well We'll see how it goes!

I assume there is a point of diminishing returns with the higher value caps? If not, I guess it could just be a matter of finding a cap value that gets me the best delay outcome.

#5 3 months ago

Yeah, there is a point where going higher can have detrimental effects. This is frequently due to an exceedingly slow rise time on the timer input which sometimes causes issues with the internal logic.

#6 3 months ago
Quoted from G-P-E:

Yeah, there is a point where going higher can have detrimental effects. This is frequently due to an exceedingly slow rise time on the timer input which sometimes causes issues with the internal logic.

Right on, thanks. I'll replace these caps for now (going with a 68uF to replace the 47uF) and we'll see what kind of time delay increase we can get. Will post updates once they arrive. Cheers.

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