Will this 'turn-on' speaker 'whump' be an issue long term?

[BTRaulerson]

Thank you for that.

[Billet]

Yes, only one side. The positive side seems most obvious, but a series cap would would function the same on either the + or - side.

[BTRaulerson]

Series would mean only on the signal (positive/red) side?

[Billet]

I would try adding a 330 uF non-polarized capacitor in series between the amp and the speaker. This will block DC and other very low frequencies from the speaker.

[BTRaulerson]

I'm a hobbyist so I can't really tell you what I'm trying to protect my speakers from. I might as well say "spooks" or "magic spark critters". There is a loud "thump" "whump" "pop" whatever you want to call it when I turn the power on or off. I have a 2.1 amp I'm making for my nephew and it does the same thing. I have a Voxel attached to the sub output on the 2.1 amp and you can see the woofer slowly push out toward you when you turn it on and it jumps back and forth when you turn the amp off. I've heard that the whole power-on pop is bad so I'm trying to prevent it. And it sounds ugly. Nobody wants ugly sound. JRT, thanks for the reply but with my skills it would be easier for me (and far more likely) to grow a unicorn bear from a seed than solder tiny wires to chip. Me and Solder don't really get along. And in all seriousness, thank you all for trying to help me.

[JRT]

This amp: the TDA7492: https://www.parts-express.com/tda749...2x50w--320-606

creates a bit of a turn-on 'thump,' a few seconds after turning on the power, but only when connected to the video preamp board It's connected to. With the board disconnected, there's no turn-on thump.

Here is a GIF of what it looks like: https://drive.google.com/file/d/1CNB...ew?usp=sharing

I think the woofers will tolerate it, but the tweeters, I'm not sure how they'll like it long-term. Of course, they're crossed at 6,500 Hz, so that IS pretty high.
Also, it's not really audible, it's just a bit of DC offset going on for a split-second.

Should I even worry about this at all? This is for a table radio setup by the way.
I do have a DC to DC transformer that will take the 24v and reduce to 12v and isolate it as well for the preamp faceplate. Is there a possibility that isolating the preamp that way will eliminate the thump?

TomZ

If the first 100 thumping events don't damage anything, I don't see why 10000 more would change that, until there is some other problem such as failed capacitors.

The TDA7492 data sheet (Google found it available for download on ST's website) shows available functionality for standby and mute modes, and the external circuits needed for that. For description see sect 6.1 and for example application see figure 28 in sect 5. Perhaps you might be able to temporarily remove the heat sink (screw heads are on the bottom side of the board assembly) and solder some small wires to the pins 20 and 21 (maybe use insulated wires scavenged from scrap Cat5 cable), and assemble the additional components in a dead-bug style external and adjacent to the board assy.

https://www.st.com/resource/en/datasheet/tda7492.pdf

While you are in there, consider upgrading C23 power supply bypass capacitor.

[tomzarbo]

So what's the speaker protection circuit supposed to do? Protect them from what?

I Think it's basically a timed relay setup. After power-on, the protection circuit timer starts which 'waits' for a few seconds for the amp to produce it's turn-on 'thump' before the speakers are actually connected, then it connects the speakers via a relay. Many if not most retail home amps have, or used to have something similar built-in.

TomZ

[DeZZar]

Everything worked fine until I added a "speaker protection circuit

So what's the speaker protection circuit supposed to do? Protect them from what?

[BTRaulerson]

Sorry for hijacking an old topic but I'm having the same issue but mine is immediately upon power-up. I get a loud thump or pop upon powering up the amp. I'm running a small class D amp rated at 80 watts per channel using a TDA3116 chip. I'm using a front panel interface that offers USB/FM/AUX/Bluetooth inputs that operates on 12 volt. I'm using a buck down converter to take the 24volt input down to 12 volts for the front panel. Everything worked fine until I added a "speaker protection circuit". Now I get no output to the speakers. The red light stays on but the green never comes on. I ran positive and negative through the circuit and also bypassed the negative and left the positive connected. I've tried 2 different types of protection circuits, 1 with separate AC/DC inputs and 1 with universal voltage. What am I doing wrong?

[AEIOU]

So, it would seem that your video preamp board has the problem.

[Millstonemike]

Okay, thanks.
I'll mess with that a bit since I have the parts to do so easily.
TomZ

Tom, There's the delay relay module I've mentioned before. The 12 V version should not suffer the issues I had with the 5 V version: ~$2-3 on Ali. It will power up up with the system power, then switch some seconds later (adjustable potentiometer - sec.'s to min's). The relay contacts handle 15 A. The relay coils would drain ~50 ma at 12 V from the main power supply. You'd need two (L-R) between each amp output and speaker input.

Having said that, if the amp is quiet, maybe it's the video board's signal after power up. You could try adding a capacitor between the video board's output signal and the amp's input (1 cap on each L-R signal). I'd start with 1 uf and work my way down. But at very low values you'll start to lose bass in the signal (e.g., 0.1 uf creates a 1st order HP at ~30 hz at the amp's input). That's equivalent to adding large HP caps on the woofers.

But if the thump is multi-seconds after power-up, signal caps may not help. Must be the video boad's circutry enabling something some time after powerup. And that enables a "thump" in the signal. But it will remove low freq. content, where the woofer excusion is worst. Trying a couple small cap values may yield some good results. And it's not, yet, another couple modules complicating the build.

Of course, the relay solution can be adjusted from1 sec beyond tens of seconds.

[devnull]

Thanks guys for the suggestions.

Devnull, I checked out that delay speaker connect board, but I'm pretty sure the thump happens at about 3.5 seconds to 4.5 seconds from memory, I'll have to double check tonight though.
That would be a decent solution, not too expensive either.

David,
would you put the cap inline of the (+) line to the woofer?

TomZ

Might be adjustable I've never played with that particular board. You could roll your own with a similar style board designed for time delayed turn on for DC and control a relay or two.

Edit- I took a quick look at the data sheet. The delay on the board is adjustable by changing a couple of through hole components after doing some math.

Another Edit - Looks like literally all the boards use the reference circuit from the data sheet. Changing the 56K resistor should be all that's needed to change the time delay.

[tomzarbo]

Hi, Tom

Between the amp and the crossover, either leg will break the circuit.

Okay, thanks.
I'll mess with that a bit since I have the parts to do so easily.
TomZ

[davidB]

Hi, Tom

Between the amp and the crossover, either leg will break the circuit.

[tomzarbo]

Thanks guys for the suggestions.

Devnull, I checked out that delay speaker connect board, but I'm pretty sure the thump happens at about 3.5 seconds to 4.5 seconds from memory, I'll have to double check tonight though.
That would be a decent solution, not too expensive either.

David,
would you put the cap inline of the (+) line to the woofer?

TomZ