Construction of a bluetooth speaker with mp3 player. Connection method.

Hello to all Forum members,

I need help completing the bluetooth speaker.

I made a 350x150x150mm box made of plywood with 2x 30W two-way broadband speakers on the front panel, plus a bluetooth player panel with other functions. Below, I paste a simplified diagram as I connected everything:



And now a description of the problems with this construction:

1. At the moment, the bluetooth player is powered from the outside by a 12v power supply, it was previously connected together with the amplifier to the battery supply, however when turned on, you could hear crackling and squeaking from the speakers . On two separate power sources there is no interference. how can i connect both elements (amplifier and bluetooth player) for the battery pack so that there are no glitches or interference ??

2. The problem occurs when louder listening to music, with moments with bass the sound from the speakers temporarily stops as if electricity was missing ?? what can I do to get the speakers running smoothly even at higher volume levels ?? I plan to mount a potentiometer between the player and the amplifier. Will the use of any capacitor eliminate sound fading? maybe replacing the wires with thicker ones?

3. The batteries are currently connected in parallel with one charger because I am waiting for the shipment with a 4S balancer and then it will change the design of the power module

4. The last problem I have is clearly audible noise during silence at the moment when the whole set is turned up, more precisely: on the 30-degree scale of volume control on the player already on the 1st level it is loud enough (for quiet listening to the background music the first volume level is enough!) the noise appears already from around the 5th grade and is getting louder and louder.
How can I eliminate this noise during silence?

I am asking for some tips from more experienced colleagues, I think some of the problems I have described have already been processed or are funny for him, I am asking for understanding I am a beginner in this field.

Rumford wrote:

At the moment, the bluetooth player is powered from the outside by a 12v power supply, previously it was connected together with the amplifier to the power supply from rechargeable batteries, but after turning on you could hear crackling and squeaks from the speakers. On two separate power sources there is no interference - how can I connect both elements (amplifier and bluetooth player) to the battery pack so that there are no glitches and interference ??

Galvanic isolation converter? Maybe just filter the BT power supply? Remove ground loop (cut signal wire shield between modules)

Rumford wrote:

The problem arises when listening to music louder, at moments with bass the sound from the speakers temporarily disappears, as if there was no electricity ?? What can I do to achieve smooth speaker operation even at higher volume levels ?? I plan to mount a potentiometer between the player and the amplifier. Will the use of any capacitor eliminate sound fading? maybe replacing the wires with thicker ones?

Check that the battery voltage is not "squatting" under load below the minimum acceptable by the inverter. If so - you need batteries with a small Rw or more "ordinary" batteries.
If the voltage of the batteries does not sit down, you probably have a problem in the inverter (current capacity is too low) - replacement with a larger, maybe ad-hoc electrolyte with a large capacity.

Rumford wrote:

The last problem I have is clearly audible noise during silence when the whole set is turned up, more precisely: on the scale of 30 levels of volume control on the player already on the 1st stage it is loud enough (for quiet listening to the background music the first volume level is enough!) Noise appears already from about the 5th grade and up is more and more loud.
How can I eliminate this noise during silence?

Do you have any gain control in the amplifier? Because it seems that the signal from BT is too strong, if there is no regulation then reduce the signal between the divider modules. Such suppression is also likely to reduce the problem of power interference, so start with that.

Added after 8 [minutes]:

Rumford wrote:

3. The batteries are currently connected in parallel with one charger because I am waiting for the shipment with a 4S balancer and then it will change the design of the power module

This will require replacing the charging / supervision module, the converter will also have nothing to do with the amplifier.

jdubowski wrote:

Galvanic isolation converter? Maybe just filter the BT power supply? Remove ground loop (cut signal wire shield between modules)

Please expand this thought to remove the ground loop .. How to filter power supply ??

Today I connected the 50k line B potentiometer but with theoretically correct connection it started humming in the speakers and as if to turn off the signal every now and again with increasing humming. I combined with the contacts on the potentiometer and finally found a configuration that has no buzzing, namely: signal cables as needed I / O, but the weight on one contact as in the picture below:

when connecting the mass as it should be, i.e. cables separately there is a humming in the speakers, I'm starting to suspect that somewhere the mass is "escaping" or somewhere there was a micro short circuit when soldering.
Any ideas for advice?
(I will add that the music is still playing at a minimal volume down on the potentiometer, but a little quieter, too weak resistance of the potentiometer ??)

Several problems were solved:

- fading out when the bass hits loud and harder - the fault was on the power supply side, there were voltage drops, it was enough to give a capacitor to a fairly capacious extent to compensate for voltage drops, I had 470nF capacitors at 16V and I gave 4 pcs. they are enough.

- crackling and squeaking about which I wrote in the first post I eliminated by desoldering everything, and again carefully soldering using goldpinów to the plates and thick 0.75mm cables, so far I do not know what was the direct cause of squeaks and glitches but these actions helped.

-What to the potentiometer I installed was a bad choice should not be linear (unless someone can match the resistance of the potentiometer perfectly - I can't ) only logarithmic whether exponential I do not know exactly what they are called but it is important that it has a curve characteristic, then it will turn down and increase to the maximum value. I have a value of 50k.


Problems I encountered during the construction of the speaker that I would not have committed a second time:

- e.g. painting order , it is best to paint the elements first with, for example, stain and then glue / turn further, I already painted the finished box and on the bright front panel, unfortunately, there are 'inclusions' of color and it shows, however, at the end you can paint everything with transparent varnish.
- another thing is best to put all the electronics on the back of the speaker housing, after unscrewing we have everything on top and there is easy access to each module, I at first hid everything inside but finally mounted on the back (except for the battery),
- I recommend cutting out holes for speakers from a template or something like a compass from a milling machine, it will never work out of hand
- and the last thing if someone cares about the tightness of the loudspeaker chamber, if you use the player like me with a panel on top, the air will escape through this panel, through the aux input, via USB, it is worth sealing this panel somehow from the inside.


This information is given as if someone wanted to build a similar speaker and had similar problems, they already have an explanation.

I am still planning to mount the passive membrane on the back of the housing.
Maybe I will also add a USB output to charge the phone - power bank function.
And a few photos with the effect:

Rumford wrote:

-What to the potentiometer that I installed was the wrong choice should not be linear (unless someone can match the resistance of the potentiometer perfectly - I can't ), only logarithmic or exponential, I do not know exactly what they are called but it is important that it has a curve characteristic, then it will turn down and increase to the maximum value. I have a value of 50k.

You can fix this problem in a simple way - between the slider and mass you turn on a resistance with a resistance close to 1/3 of the track resistance (for a 50k potentiometer it will be 15 or 18k. The resulting characteristics will be close to logarithmic.