This could probably also go in the sections for analog/mixed circuits or power circuits but I'm pretty sure my problem is pretty basic.

It's been years since I dove any deeper into electronics than Ohm's law and connecting sensors to arduinos and so on.

I'm putting together a bookshelf bluetooth speaker, building a new cabinet and using the guts from a decent pair of desktop Yamaha amplified monitor speakers, and a basic bluetooth module.

Right now the electronics are a pile on my desk and work fine if I run the amp from a 12V bench supply and the bluetooth module from a USB brick. But when I power the BT module from a 5V adapter powered by the bench supply, I get whine. I've tried a 5V regulator module from AMZ. Also tried a 7805 TO-220 bare regulator, and the 7805 with capacitors from the legs to the ground in a variety of values.

A specific question about capacitors. Should those be electrolytic, ceramic, film? I think I've seen online references to using ceramic but the values described don't seem to be widely available for ceramic.

I've also seen a lot of mention of ground loops. FWIW All my grounds are tied together with no more than a few inches of solid copper wire between them.

And in general, can anyone point me toward n00b-level guidance on eliminating the whine, or a reasonably simple schematic for a 12V --> 5V adapter that won't whine?

 

How much current will the 5V system need?

 

How much current will the 5V system need?

Trivial. A little Bluetooth board...

 

I've been trying combinations of capacitors across the input and output leads based on online examples, in general they seem to call for electrolytic caps and about a 10:1 ratio between the ones on the input and output. No change. Any guidance is welcome.

 

It would appear, from your description, that the bluetooth module is susceptible to noise from your bench power supply. What do you plan on using for a supply for the completed speaker? If not the bench supply, then don't waste time trouble shooting it. Check it out with the intended supply. Let us know what happens.

 

Trivial. A little Bluetooth board...

Measured it. 10-15 mA

 

It would appear, from your description, that the bluetooth module is susceptible to noise from your bench power supply. What do you plan on using for a supply for the completed speaker? If not the bench supply, then don't waste time trouble shooting it. Check it out with the intended supply. Let us know what happens.

Good point. Was planning on a wall wart. Let me find the one I hope to make permanent.

Bench supply is a Dell ATX power supply with a breakout board/kit, BTW.

 

Good point. Was planning on a wall wart. Let me find the one I hope to make permanent.

Bench supply is a Dell ATX power supply with a breakout board/kit, BTW.

OK. 12V 1.5A wall wart that came from a different set of amplified speakers has the exact same noise.

Whine is high pitched, BTW, not a 60Hz hum. Don't know if that's relevant.

 

Hello,

Could it be that the wall wart is a switching power supply?
A switching power supply uses a high frequency switching circuit.

Bertus

 

Only when the USB powered BT is ON

work fine if I run the amp from a 12V bench supply and the bluetooth module from a USB brick.

So why not just use the USB Brick?

 

Only when the USB powered BT is ON

So why not just use the USB Brick?

The amp needs 12V and the BT module uses 5V. Planning to run this from a single 12V input.

 

Hello,

Could it be that the wall wart is a switching power supply?
A switching power supply uses a high frequency switching circuit.

Bertus

I'm pretty sure most/pretty-much-all wall warts are switching power supplies, which I know are problematic. But they also work just fine for many other systems including amps/speakers. I'm hoping I can use an easily available wall wart...

 

Sound like your bluetooth receiver is bad.

I have used this one in a pair bluetooth speakers I just built. It works fine with multiple 12 to 18V supplies I have tried. And it is both the receiver and amp on one tiny board. No noise, excellent sound, plenty of power.

 

Sound like your bluetooth receiver is bad.

I have used this one in a pair bluetooth speakers I just built. It works fine with multiple 12 to 18V supplies I have tried. And it is both the receiver and amp on one tiny board. No noise, excellent sound, plenty of power.

Your link appears to be specific to your AMZ account but if you mean the red one that powers speakers directly and runs from a lithium battery, I've used that one for other projects. In this case I need a little more power and my customer (wife) wants a volume knob. The customer is always right?

OK, the one you list isn't the one I was thinking of, I was referring to this. Yours would work if I can pigtail out the volume pot and switch out to the panel. But I have a requirement from the project sponsor (wife) for an aux input.

 

Hello,

@BobTPH , the given link at amazon is a "buy again" link.
It will not show the product.

Bertus

 

Sorry this thread is getting convoluted, I need to better learn how to reply inline with questions.

I also have a 24VAC wall wart on hand (I'm trying to do this whole thing without spending a lot on new gear). I might pick up a rectifier or cobble one from diodes on hand. I have 7805 and 7812 on hand. Basically build a separate 12V/5V linear power board.

Or is a linear wall wart likely to not have this problem? Like this one?

Update: I have a 25A bridge rectifier on hand. Now I need a bigger amp!

Updated update: That AC wall wart is dead. Will order the 12VDC linear wart.

Feels like I am not making positive net progress on this project.

 

3D printed speaker box and grill with built-in bluetooth receiver. I am quite happy how this came out. 25x13x15 cm. Tuned bass reflex. -3dB at 57 Hz. ~1Kg of ABS.

 

3D printed speaker box and grill with built-in bluetooth receiver. I am quite happy how this came out. 25x13x15 cm. Tuned bass reflex. -3dB at 57 Hz. ~1Kg of ABS.

View attachment 348822

A whole roll of ABS? That would give it some gravitas for sure.

I'll update here when mine is done!

 

A whole roll of ABS? That would give it some gravitas for sure.

I'll update here when mine is done!

Yep, I made the walls solid 5mm to get enough stiffness. It does not vibrate at volume levels way above what I would ever use. The entire unit weighs 2Kg (4.4 lb.)

 

MOST of the current five volt power supplies are switchers, and for battery charging not much filtering is required.
So if you have room for it, use an older type wall wart supply that has a transformer. Those are the heavy ones. With a higher voltage you can afford a bit of voltage drop in the filter, and then use a five volt linear IC regulator to provide a clean five volts. THAT should solve all of the noise issues.