Noisy powered speaker

[Andy Burns]

I have a Vava Voom portable speaker, no longer available, not even on the manufacturer website any more

It used to sound very good providing you didn't use any of the "enhanced" modes, remarkably heavy for its size, but now it makes an annoying frying/burbling/warbling sound whenever it's playing (it self-mutes when not playing anything).

It has inputs from Bluetooth or 3.5mm jack, not WiFi. It can be powered from 5V USB, 15V barrel jack or internal Li-ion cells. It makes the noise on all power sources, and all input sources.

It spends most of its life on external power, and the batteries eventually died so they've been recently replaced, it was a real pig to open, while I was soldering in the new tagged 18650s, I hoped I might see some dodgy electrolytics that could explain the noise but nothing looked dodgy, some photos of the amp board ...

The various JST-type plugs go to battery protection board and speakers

The ribbon cable goes to the top panel with LEDs, buttons and NFC/BT module.

The red gunge on the two larger capacitors isn't leakage, just some sort of silicone applied to glue them together, I can't see anything worthwhile replacing there, can you?

[Bob Eager]

I've had that on amplifiers and it was a noisy resistor! Also remake any soldered joints that look suspect.

Freezing spray might help to localise it.

[John Rumm]

It could be that digital noise is getting through into the audio stage - perhaps a failure of a filter component. Just because the caps are not visibly damaged does not mean they still hold there original capacity or have not gone high ESR. Given there are not many electrolytics, I would be tempted to swap them out anyway before getting too deep into further investigation.

[Clive Arthur]

<snip>

I'd change the amplifier chips, TPA3118 - RS sell them for not much, probably cheaper elsewhere. They're class D amplifiers so are efficient and don't require heat sinking, but they're still going to get warm.

[Andy Burns]

Oh, I'd assumed the ICs would be the least likely parts to degrade ...

[Andy Burns]

£1.03 each with free P&P sounded good, until the P&P changed to £17.98 :-(

[The Natural Philosopher]

Is that distortion that varies *with* the signal, or an *additional* noise? Does it happen on the analogue jack input?

[The Natural Philosopher]

You would in general be correct. They don't degrade, they DIE horribly and in pain. Pots and other mechanical devices including solder joints are no 1. Electrolytic and high voltage capacitors are No 2 and 'everything else' is no 3.

Burbly frying noises are often symptomatic of RF instability. which can be a bad capacitor.

[Brian Gaff]

Well like yourself, it does sound like inverter pick up. Many of these devices have the dc voltage internally higher than the supply voltage, and use an internal switch mode inverter to generate the voltages, so it really is probably a suppressor component on the inverter or dodgy cap as you deduce. Could be really just worth getting a circuit and seeing if there are any likely culprits and swapping them out.

Brian

[Brian Gaff]

I had a sub woofer and some gunge they had stuck around the components went slightly conductive due to moisture in the air. Sadly, it now has a problem where the protection relay makes a bad connection sometimes, turning it off with a bang. I do honestly wonder whether components are just not made so well any more. Brian

[Brian Gaff]

So would I those either work or don't usually its something else. I've never really understood class D. This was experimented with by Clive Sinclair many years ago, but they did not sound very good and chucked out a lot of interference. Brian

[Andy Burns]

Doesn't vary with the signal, or the volume level, just a background mushy noise, the frequency of which wanders up and down, its most noticeable with an input connected but nothing playing.

Yes, as long as something is plugged in (even a 4" plug to plug lead connected to nothing) it makes the noise, so presumably the jack is one of those with a physical switch incorporated, so it "knows"; as soon as it's unplugged it mutes itself.

The whistling doesn't alter with the volume control (though a background hum does increase with volume) here's a recording

[The Natural Philosopher]

Interesting. sounds like filtered white noise. 'wind in the willows'.

Hmm. An educated guess is that its doing RF oscillations at some level. Without a scope it's hard to be sure.

check for something like a dry joint on a *small* capacitor.

[Andy Burns]

It's semi-assembled with the the case hanging off, but other than making up five JST extension leads, no chance of getting my mits anywhere near it with scope probes, even then I wouldn't know what I'm looking for really.

I can disassemble again and try that

[Paul]

It's a Class D amp. It does PWM at 1.5MHz or less, then does a low pass filter of it, for regeneration of base band. By using output transistors in saturation (inside the TDA chip), the efficiency of the amp is very high.

Some of the filtering visible in the picture, is to prevent noise from going back on battery (and using any battery cable as an AM broadcast antenna).

If the PWM did not work at a constant frequency, perhaps modulation of the PWM operating frequency, would come through in the base band ?

Could there be a DSP hiding on there somewhere ?

How do the control buttons connect to the circuit ?

I feel like a portion of the circuit is missing. Another circuit board ?

And that glue to protect the electrolytics from vibration, that's nasty stuff, but it does not look like it has caused obvious damage in this case. On some devices with amps-in-sub-box, the copper tracks get eaten by the corrosive glue. The glue did not do that initially, but as it ages, and spends time at elevated temperature, it decomposes into "something else".

That glue idea, has destroyed a fortune in audio equipment.

One thing I don't know about Class D, is how much effect the ripple currents in the low-pass filter, affect capacitor life, and whether Class D eventually fails at the filter level.

The capacitor seams are intact, but that does not necessarily mean the capacitance value is still at the original level.

For people using Audacity at home, with your audio sample, snip the last little bit off the end of the sample, then select-all and Normalize to whatever level you want. That could make the sample easier to hear.

I was expecting to hear a bit more "burbling" (old cellphone noise), but the noise isn't exactly like that.

Paul

[The Natural Philosopher]

all well and good, but it is unlikely that the class D amp could produce that particular effect.

Again I cant see how it would

Dunno.

No. It sounds more like white noise and a voltage controlled filter :-)

[Andy Burns]

I don't have any freezer spray (or equivalent) I doubt acetone evaporating would make much difference, tried tapping inductors and capacitors, probably pointless but nothing changed the whistling.

touching the input stages and the actual chip pins does introduce hum as you'd probably expect, but doesn't change the characteristic of the noise.

Here's the underside of the board, not very legible, it's not as horrific as I though when I first saw it, that's resin that spilled from where it's glued to the case, not battery juice.

Through that foil-wrapped flex/ribbon in picture1, the buttons are about

6" away, nothing changes if I touch the pins on the connector for them

Yes, as i said there's a separate board with the buttons and a sub-module for bluetooth and NFC and mic, though I'm only using it as an analogue amp/speaker, I use the "smarts" of a chromecast audi to feed this thing, yes that's wifi but the whistling happens even with the chromecast unplugged and powered off, so it's not related, the chromecast is USB powered, and if I do power it from the USB outlet on the speaker it picks up horrible digital noises, makes it unlistenable.

For the two large ones, I could desolder one leg and measure them.

I've normalised and re-uploaded the file, in real life I just hear the warbly/whistly noise, the loud his is probably from normalising it to be too loud.

same URL

[Paul]

OK, the amp-pcb3 picture shows a power converter. That is changing battery voltage to something else. And with a 5 amp rating, it might be powering the amp chips.

It's on the FCCID site.

VASKXX Bluetooth Speaker User Manual VAVA VOOM _20150911_V4.0-OUT-1 SUNVALLEYTEK INTERNATIONAL

The resolution of the images in the PDF is such, as to make the pictures useless. Can't get any info on the chip under the resin.

The control board, one of the chips has a quartz crystal.

Paul

[Animal]

I'd suspect a bad electrolytic cap(s) as the cause of that noise. Press a new/good cap's leads onto each old one in turn while it's operating, if you hit a bad one it will clear up.

[Rod Speed]

RF, easy to look for.