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

[tomzarbo]

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

[rpb]

I think if you don't hear any treble, there should be no strain at all on the tweeter. Someone correct me if I'm wrong, but I think you could connect dc voltage to a tweeter protected only by a cap, and no current would flow through it. I did notice that the woofer cone seems to protrude a bit even between the whumps. The surround looks like the cone has already moved outward. (Perhaps an optical illusion.) Does it look like the cone is centered properly to you?

[tomzarbo]

It is hard to see in the gif, but the cone is centered at rest before the whump. And the cone only moves out from center, then back to rest... It never moves in from center.

I don't hear any high freq sounds at all. If you don't actually see the come moving, you would never know it happened, it's basically silent.

TomZ

[devnull]

do a search on ebay for "UPC1237 Dual Channel Speaker Protection Circuit Board DC 12-24V Boot Mute Delay" should do what you need. Cheap protection for the speakers.

[davidB]

Hi Tom,
Just put capacitance in front. This is why I have a bag of 100v 150&100mfd caps around.

Use as little as you can w/o changing the useful bass.
If you want to sim it, start around where you exceed xmax.

Getting close to that point gives protection from excess EQ
. Saves amp power, your little amp won't try to write a check that your speakers can't fill.

[wogg]

Short answer: No. That won't cause a problem, especially since it's inaudible.

[philthien]

Automatic woofer suspension break-in 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

[davidB]

Hi, Tom

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

[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

[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.

[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.

[AEIOU]

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

[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?

[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?