Bluetooth adapter for connecting to an amplifier. MP3862BT Built-in Bluetooth module for an amplifier, active speakers or radio with hands free mode
Audio power amplifiers (AFPA) occupy a special place in electronics and are used everywhere: in audio systems, TVs, CDs, MP3 players, etc. Almost every radio amateur, at least once in his radio practice, assembled an UMZCH and was glad that the board with wires produced sound. But that’s not about that now. Nowadays, despite the many ready-made designs, we still assemble our audio systems ourselves. And I turned out to be one of those who assembles my own audio system. I have been using the Radiotechnika U-7111 amplifier as an amplifier for many years. Using this amplifier to listen to music, I was not happy with the fact that there were always a lot of wires to connect the audio signal. This was especially inconvenient when connecting a phone, which prompted me to make this modification to the amplifier.
The modification is to install a Bluetooth audio module (BAM) into the amplifier. After a little searching on the Internet for various options, I set my sights on BAM BK8000L. It costs only $1-2 and is sold on AliExpress. Photos of this module are presented in the figures below.
This module has the following functionality:
- switching tracks;
- the ability to pause a track;
- volume control;
- microphone connection;
- AUX connection;
- sound indication of low battery charge;
- control from a personal computer (this functionality is available when updating the module firmware).
We'll probably stop there. Moving directly to the installation and connection of the BAM to the amplifier. And so on in order.
BAM connection diagramBK8000L
Let's take the standard connection diagram from the datasheet (see figure below), but with the condition that additional BAM functionality will not be used. In this regard, the connection turned out to be simple and is carried out according to the diagram below, the right side of the figure.
BAM connection diagramBK8000L to amplifier
After thinking a little and deciding that the input from the pickup had never been used, the decision was made to connect the BAM instead (when this input is activated, the BAM can be connected to another unused input (you need to look at the electrical circuit diagram of this amplifier). The connection is made according to the diagram see the figure below.To do this, you need to unsolder capacitors C8 and C9 from the output of the corrector amplifier, marked with red crosses in the diagram, and solder them to the AUDIO_LP and AUDIO_RP BAM outputs.
Connection diagram of BAM BK8000L to the power source
After studying the information on this BAM I came across the following problem. Almost everyone who uses this module complains about digital noise, which can be heard very loudly in the speakers when playing music. This problem was solved only by separating the power supply of the amplifier and the BAM. To do this, we will use the connection diagram shown in the figure below.
1. We make the transformer from a stationary transformer by winding another winding on top of the section, from which this BAM will be powered in the future. To wind additional winding onto the transformer, it is necessary to remove the cover and bottom wall from the amplifier, thereby providing free access to the transformer (see pictures below).
After ensuring free access to the transformer, we wind the additional winding with twisted pair wire, having previously dissolved it into cores. The additional winding contains 40 turns of this wire, and its length is about 7 meters. Then we fix the winding terminals and the wire itself along the entire length with hot glue. The winding of the wire can be seen in the figure below.
2. The rectifier/filter is made from any existing diode bridge and an electrolytic capacitor of 470-1000 uF at 16 volts. The installation is carried out in a free place near the transformer (see figure below).
3. We use the factory-made down converter HM-MINI-360 (see figure below). Having previously connected it to the rectifier / filter and set the output voltage to 4.2 volts. We also install the converter in a free space near the transformer (see figure above).
4. BAM BK8000L is installed in front of the amplifier under a plastic casing near the volume control (see figure below). This installation location will increase its range due to the lack of shielding by a metal case.
The pictures below show photos of this amplifier modification.
List of radioelements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad |
|---|---|---|---|---|---|---|
| Diode bridge | 2W10 | 1 | To notepad | |||
| Electrolytic capacitor | 1000uF | 1 | 16v |
A USB Bluetooth audio adapter will allow you to turn any amplifier into a wireless gadget for playing sound. The USB Bluetooth stereo adapter can be connected to a car radio, stereo system, active speaker system and play sound from a phone, player, game console, laptop, etc.
Using a USB Bluetooth wireless stereo receiver, you will instantly get rid of unnecessary wires, enjoy digital stereo sound quality and all the delights of wireless control. The Bluetooth adapter is small in size and designed in the form of a flash drive, which allows you to take it with you anywhere.
Connection.
To connect, you need to insert the Bluetooth adapter into any USB input to receive power. Then connect the audio cable to the AUX input of the amplifier. All manipulations will take you no more than a minute. For power, you can use a separate power supply, say, from the same cell phone with a USB output. AUX is a linear input, now found in almost any device that has a power amplifier, so finding it won’t be difficult. Once connected, the LED on the adapter will blink briefly, indicating it is ready for use.
Pairing.
On the device you want to stream music from, search for bluetooth devices. In the found list, select “dmzmusic”; if, when you try to connect, a window appears asking for a password, enter “0000”, after which the pairing will be completed (the LED on the bluetooth receiver will blink at long intervals). Now you can play music through the amplifier's speakers.
Review of an interesting and compact amplifier with Bluetooth on board, a wide power range and good characteristics.
Packaging and delivery.
Order processing lasted 2 days, delivery another 13 days.
The track was issued, full tracking, from dispatch to my post office.
The impression of the store and delivery is good.
I picked up a typical Chinese black light package from the post office; it didn’t inspire much confidence since it was quite thin. 
Having opened the package, I saw the amplifier in antistatic and 4 layers of foam, quite enough to protect small elements from damage during transportation. But if the post office tries, it might break it. 
Review
<Фото в большом разрешении, советую кликнуть и рассмотреть поближе интересующие элементы.>
Back view
There is nothing remarkable here, except that there are holes for heat removal from the chip to the bottom of the printed circuit board where there is a large polygon. 
Chicane
There is flux snot on the contacts, it does not affect the operation, but it is clear that the board was not washed after soldering the connector. 
Board Dimensions
The board is 5cm wide 
Length 8cm 
And 1cm thick
Ts 50x80x10mm
18650 for comparison 
Type of connectors
The connectors for connecting the speakers are very convenient, their design is made so that they do not squeeze out the wires (unlike cheap terminal blocks). The size is sufficient to connect fairly thick and tinned wires.
Power connector
The power connector is universal or made with a good margin. Almost all modern laptop plugs fit into it. 
The board can be powered from 8 to 25 volts, nominally 20 volts.
When powered by 3x 18650, no problems were noticed, either with fully charged or with discharged ones, up to 2.9V each.
At the power input there is a diode against over-reversal. If you install the amplifier in a finished device, the diode can be removed to avoid a voltage drop (about 0.3V).
There is no capacitor on the power line, just as there is no place to put it, I assume that the power supply for this module is meant to be from batteries, where this very capacitor is not needed. 
Bluetooth module and pre amplifier
The pre-amplifier is made on the N5532 chip
I can’t say anything interesting about it, it’s an ordinary low-noise two-channel operational amplifier.
Thanks to the large power supply range, you can connect a wide range of power sources to the device, ranging from 18650 batteries (3 pcs in series) to power supplies for laptops.
The manufacturer promises 90% efficiency (which, with an output power of 50 watts, gives 5 watts of heat.)
Recommended characteristics - 2 channels of 25 watts with a speaker impedance of 8 ohms and a power supply of 20 volts.
A small clipping from the datasheet 
The microcircuit is designed to work in TVs and monitors, but nothing prevents you from using it for your own purposes - to work with a Bluetooth module.
Although the chip has a fairly large output power, it does not require active cooling; all heat goes through the substrate and is distributed throughout the board.
Even under intense loads, there is no significant heating of the board and microcircuit.
You can also see a double switch on the board; all it does is change the signal amplification mode. But I don’t see the point in it, because if you switch any of the switches to ON, noise will appear (interference from bluetooth).
The store page has an excellent description of the amplifier's controls and connections.
The purpose of the buttons is duplicated on silkscreen printing. 
Compound
Establishing a connection with Windows 10 On PC
I have an Asus rog gl552vw laptop, but the onboard module is from Intel with wifi and bluetooth 4.0
To connect the amplifier you need to go to the bluetooth parameters (click on the cloud in the panel below
then right-click on the bluetooth icon and select “go to settings”
A list of available Bluetooth devices will open.
We select our amplifier; it is highlighted by an icon in the form of headphones. 
Click connect and wait for the connection. 
After connection, 2 new devices will appear in the volume control panel.
The sound will be terrible. 
As the default device, “headphone” is selected, click on “headphones” and click on the “default” button at the very bottom of the window. Now the sound will be of normal quality.
A little information
The headphone has a low-quality audio format and is intended only for conversations. 
The headphone mode has acceptable quality for music. 
About the Bluetooth device 
Connecting to Android
Turn on Bluetooth, go to its settings, find our amplifier in the devices section, click on it, wait for pairing. 
After pairing, you can turn the wireless headset and wireless media stream receiver on and off. 
When adjusting the volume, the smartphone speaker adjustment slider changes to the Bluetooth device volume adjustment slider. 
Tests
Foreshadowing questions about the video - there won’t be one; assessing sound quality using a smartphone’s microphone is, of course, stupid.
Sound quality is a solid 4. Bass cuts only at the highest volume
High frequencies are not reduced.
I also have a MASTERKIT BM2039 at home on a TD8560Q chip (I bought it a long time ago before the crisis for 150 rubles), it produces a little more bass and plays cleaner at high volume, but at the same time it heats up MUCH more and has only 12V power.
Conclusion
The impression of the product is purely positive, the problem with power supply is very easily solved by purchasing a regular power supply for laptops; a standard 19V 4.7A power supply will not even heat up during operation.
Good characteristics allow you to listen to music at an acceptable volume without loss of quality.
The wireless connection turned out to be very convenient, no more wires are needed, connect your smartphone, turn on the music and continue using your smartphone.
If you use it at home, you can connect 2 devices at once - a PC and a smartphone, the Bluetooth module will look where the sound comes from and play it, without manually switching the signal source.
Also, when used in a car, you can install a microphone and get a Hands free headset.
The only thing that spoils the impression is the very quiet noise from the Bluetooth module.
pros
-Wireless connection
-Large reception radius
-Wide range of supply voltages
-Compact sizes
-Quality execution
-Easy to use
-Low price
Minuses
-Small interference and noise in the speakers
-Wheezing at very high volumes
-No plastic stands as in the photo in the store
There is also the same amplifier but with an additional line output for connecting headphones or another amplifier, the price is even slightly lower.
Progress is certainly a useful phenomenon. But, unfortunately, it has side effects. In particular, we have to come to terms with the fact that now the obsolescence of many electronic devices occurs much faster than their natural physical wear and tear. Take, for example, the music centers or complexes of stationary sound-reproducing equipment that many people have at home. Such devices can faithfully serve their owner for ten years or more. However, the rapid growth of the mobile device segment, combined with the rapid development of online services, has led to the fact that audio equipment that is still fully operational and not very old is gradually becoming less and less in demand.
Will this music last forever?
The reality is that physical media with music recordings are gradually falling out of use. And even at home, many people prefer to play sound recordings via mobile devices. At least for reasons of convenience: now it is possible to play your favorite music from online streaming services and social networks. Plus a wide selection of Internet radio stations, the number of which has long exceeded tens of thousands. And the most advanced users, in addition to this, have extensive personal music libraries on their home NAS drives.
Naturally, in such a situation, the most convenient option for delivering a digital signal from the source to the sound-reproducing device is a wireless connection. Firstly, you don’t have to look for the right cable every time. Secondly, you can move freely around the house without losing connection and the ability to control playback.
Now let's look at a fairly typical situation. There is no longer a new, but still fully functional music center (as an option - a set of block audio equipment), the sound of which you are completely satisfied with. However, due to the reasons stated in the previous paragraph, using this equipment with mobile devices is not very convenient. What to do?
Manufacturers of gadgets and accessories are ready to offer their solutions to this problem. One of them is to connect an external wireless adapter to your existing audio equipment. It receives a digital signal broadcast from a mobile device via a wireless channel, converts it into analog and, in this form, supplies it to the linear input of a music center or amplifier. Such an upgrade will allow you to extend the active life of high-quality audio equipment, providing the ability to connect PCs and mobile devices to it as quickly and easily as possible.
To test the performance of such a solution in practice, we decided to test one of these adapters produced by the famous Swiss company Logitech. The model is called simply: Bluetooth Audio Adapter (literally, “Bluetooth audio adapter”).
Acquaintance
The Logitech Bluetooth Audio Adapter device comes in a small cardboard box, decorated in the traditional white and green color scheme of this manufacturer. An interesting detail: instead of the usual cardboard or plastic eyelet, there is a loop of black cord on top.
In addition to the adapter itself, the package includes: an audio cable 1.5 m long (2 RCA - 3.5 mm mini-jack), a power supply, a quick user guide and a leaflet with warranty information. All this is neatly laid out in the cells of a tray made of thin transparent plastic.
The compact (only 50x50x23 mm) body of the device is made of plastic. Without delving into the description of the design (everything can be seen in the photographs above), we will describe it in one word - “minimalistic”. The design uses a combination of two colors: black and bright blue.
The rear panel contains two RCA sockets, one 3.5 mm mini-jack, and a coaxial connector for connecting the power supply.
A wide rubber pad is attached to the bottom plane for better contact with the supporting surface. There is a light indicator installed on the side, equipped with a matte diffuser.
In the center of the top panel there is a shallow niche in which there is a button to activate the wireless connection mode, marked with the Bluetooth logo.
Connection
The procedure for connecting the Logitech Bluetooth Audio Adapter will not cause any difficulties even for non-specialists. First you need to connect the cable from the standard power supply to the connector on the rear panel. The next step is to connect the adapter to the device to which you plan to broadcast sound. Thanks to the presence of outputs with two types of connectors (mini-jack and RCA), maximum compatibility is ensured. For example, multimedia speaker systems equipped with a built-in cable can be connected directly to the mini-jack socket. In other cases, the connecting cable included in the package will help out. Depending on the type of connectors installed on the connected device, it can be connected to one side or the other.
Using the Logitech Bluetooth Audio Adapter, you can broadcast line-level audio to a variety of devices equipped with an analog input - active speakers, stereo systems, receivers, amplifiers, etc.
The Logitech Bluetooth Audio Adapter connects to audio sources via a built-in Bluetooth 3.0 adapter that supports A2DP (Advanced Audio Distribution Profile), which provides two-channel (stereo) audio.
When you turn on the power, the Logitech Bluetooth Audio Adapter automatically enters wireless connection mode, indicated by a flashing blue light. To establish a connection, you must enable the search for Bluetooth devices in the settings of your mobile device. After displaying the list of found devices, all that remains is to select Logitech BT Adapter.
If the device you are using supports the A2DP profile, then after a short time a wireless connection will be established (in the examples given, a tablet with Android OS was used).
If you later need to connect a new device to the Logitech Bluetooth Audio Adapter, you can manually activate the wireless connection mode by pressing the button in the center of the top panel.
In progress
So, the equipment is connected, and now you can try out the Logitech Bluetooth Audio Adapter in action. After starting playback of the recording on the tablet, we heard sound from the speakers to which the Logitech Bluetooth Audio Adapter was connected. It is very convenient that the signal can be played from different applications - media player, web browser, games, etc. This allows you to listen through an external speaker system or music center to programs from Internet radio stations, recordings from streaming services (for example, Yandex. Music), etc. The sound volume is adjusted not only on the end device, but also on the tablet. The latter option is more convenient, but does not provide high accuracy due to the small number of intermediate positions.
One of the features of the Logitech Bluetooth Audio Adapter is the ability to establish a wireless connection with two devices simultaneously (for example, a tablet and a smartphone). To switch the source, simply pause the audio playback on one device and then start it on another.
During our tests, we connected the Logitech Bluetooth Audio Adapter to an inexpensive active speaker, a stereo system, and a set of block Hi-Fi equipment. In all cases, the adapter did its job perfectly, ensuring uninterrupted and high-quality sound reproduction. The wireless connection works reliably within a medium-sized room (18-20 m2) and even in adjacent rooms (through a concrete wall).
Conclusion
As we have seen from our own experience, the Logitech Bluetooth Audio Adapter is a truly convenient and extremely easy-to-use device that can serve as a link between modern gadgets and sound-reproducing equipment of different classes - including active multimedia speakers, stereo systems, receivers and amplifiers.
The main advantages of the Logitech Bluetooth Audio Adapter are high sound quality, ease of connection and the ability to communicate with two devices at the same time. It is also worth paying attention to the small dimensions and excellent appearance. I would like to say special thanks to the developers for a very delicate light indicator that does not hurt the eyes.
The disadvantages of the Logitech Bluetooth Audio Adapter model include the non-standard connector for connecting the power source, which is why the adapter can only work with the unit included in the package. It is quite strange that the developers did not opt for the more universal microUSB - after all, in this case, the Logitech Bluetooth Audio Adapter could, if necessary, be used in mobile conditions by connecting to the output of a portable battery.
To sum it up, we can state that the Logitech Bluetooth Audio Adapter is an excellent option that allows you to complement the capabilities of your existing audio equipment with wireless connectivity to PCs and mobile devices. Such an upgrade will cost much less than purchasing a new music center (and even more so an amplifier or receiver) with a built-in Bluetooth adapter, and will allow you to seamlessly integrate still fully functional audio equipment into the ecosystem of modern gadgets.
As an UMZCH I used a stereo ULF of 20 watts per channel, which costs $20 on ebay. You need to disassemble it and inspect the inside of the case to understand where to get the power from the module and where to actually place it. When everything is unscrewed, the amplifier looks like this.
Now about the bluetooth audio transmitter. It is bought ready-made.
All together - adapter and stabilizer - costs less than $8.
An disassembled Bluetooth audio receiver is shown in the photo. Connect 3 wires to the audio jack.
Now solder the wires from the USB cigarette lighter - charger.
They are both designed for power supply from 12 V. If the amplifier operates even from 24 V, it is still suitable. But if the amplifier operates at a higher voltage or is powered directly from a 220 V network, you will have to take a USB charger separately, or look for a reduced stabilized power supply on the board of the UMZCH itself. In general, you will figure this out yourself.
Now connect it to the bluetooth receiver according to the power supply on the board - this is 5 volts. Both modules are attached to an aluminum radiator, as the most massive element of the circuit.
The input wires are directly soldered to the audio out line of the amplifier, but if you want to add an active subwoofer or connect something similar, you need to drill a separate 3.5 mm output in the rear panel. Carefully secure the Bluetooth receiver itself to a suitable place using hot glue.