HowTo: TDA7492/CSR8635 - DIY Bluetooth Retro Speaker Build

Sometime last year I stumbled across the very affordable TDA7492-CSR8635 Bluetooth amplifier boards on Ebay.
These include a Bluetooth audio receiver and a stereo amplifier that can be used to control loudspeakers up to 50 watts. Well, at first I didn't know what to do with it. But a potential application should not be long in coming.

A few days later I happened to stumble across an old speaker in the basement that had a real wood look (actually not just a look. It was actually made of real wood. 😀). Since the associated amplifier had long since given up the ghost, I had the idea of breathing new life into the old speaker with the amplifier board.

How to do this and what you need to consider is described in the following article.

Safety instructions

I know the following notes are always kind of annoying and seem unnecessary. Unfortunately, many people who knew "better" have lost eyes, fingers or other things due to carelessness or injured themselves. Data loss is almost negligible in comparison, but even these can be really annoying. Therefore, please take five minutes to read the safety instructions. Because even the coolest project is not worth injury or other trouble.

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Helpful articles:
Before you start with this article, you should have dealt with the basics of soldering. You can find information about this in the following article.
Electronics - My friend the soldering iron

Required material:

In the following list you will find all the parts you need to implement this article.

Required tool:

In the following list you will find all the tools you need to implement this article.

Collect required parts

In the following picture you can see the parts needed to build your own retro Bluetooth speaker.

Print the 3D parts you need

Download all the required STL files: TDA7492CSR8635-DIYBluetoothRetroSpeakerbuilding-STL-FILES

Button cover:

You can rotate the 3D view of the STL file by holding down the mouse button. You can zoom in and out with the mouse wheel.

Connection panel normal:

You can rotate the 3D view of the STL file by holding down the mouse button. You can zoom in and out with the mouse wheel.

Connection panel including external speaker connection:

You can rotate the 3D view of the STL file by holding down the mouse button. You can zoom in and out with the mouse wheel.

Open speakers and locate connections

Before you can start the conversion, you first have to get inside the speaker.

To open the speaker you usually have to loosen all the screws visible on the back.
Open speaker with visible crossover.
Detailed view of the crossover. Here you can now disconnect all (hopefully) plugged-in connections and put the back aside for now. You won't need these again until later. But be careful: take a photo of it before disconnecting the plug connections. This means you can easily understand later which plug goes where.

Attach the button cover

After you have opened the back, you can begin the first cosmetic expansion of the speaker. So that you can later adjust the volume and control the playback of the music, the associated buttons must be moved to the outside. This happens in the following steps.

Positions the button cover in the middle of the top of the speaker. To do this, use a ruler (or similar) to check that the distance to all sides is the same.
Once you have aligned the button cover, you can drill the first mounting hole. Before drilling, it is better to check twice too much than once too little to ensure that the panel is actually in the right place.
Did you drill the hole... bring both “into line” again and temporarily insert a screw through the panel into the drilled hole. So you have already created a “reference” so that the remaining holes are all in the correct position.
Before you drill the next mounting hole, you should check again that the button cover is parallel to all outer edges of the speaker. This can be done, for example, with a large set square.
If the button panel is correctly aligned, you can drill the next hole...
...and temporarily fasten it again with an inserted screw. Now the panel is secured against slipping in all directions.
You can now drill the remaining mounting holes without the panel slipping.
Now the holes for the actual buttons still need to be drilled. To do this, drill a hole in the top of the speaker in the middle with a small drill, as shown. A drill diameter of 3mm is sufficient here. The holes are “drilled” to larger diameters in the following steps.
Once you have drilled all the holes you can...
…remove the cover again.
Now it's time to drill out the holes you just pre-drilled with a “flat milling drill” - i.e. bring them to the actual size. Of course, the drill should be slightly larger than the diameter of the buttons that will be used later.
It is better to drill the holes with the “flat milling drill” at a slightly lower speed. This means you can react more quickly if the drill gets stuck. Before drilling, also check that you do not damage any components on the inside of the speaker when drilling.
Have you drilled all the holes... can put the button cover back in and check whether all the holes are big enough and everything generally fits.
Now that you know that the speaker is ready for the fully equipped button panel, you can start to completely equip it. To do this, push the buttons from the top of the button cover through the holes for the buttons...
...and secures them on the back against falling out with a union nut.
So that the buttons can later be connected to the amplifier board, you now have to prepare six double cables. (Here you can - if you have one - recycle the previously separated speaker cable.) These should be long enough so that you can easily solder the cable to the amplifier board later. If you are unsure about the length, it is better to have a little more length than too little. In most cases you should be able to handle a length of 30cm very well.
Then remove about one cm of insulation from all ends of the double wire and tin it with solder. This ensures that the strand of the individual cable does not “unravel” later.
Now you tin plate the contacts of the buttons...
...and repeats this for all other buttons. This means that soldering with the previously tinned double cable later is a piece of cake.
Before you solder the double cable to the buttons, you can shorten the stripped part of the double cable a little. Five mm is completely sufficient here.
Then try to heat the solder already on the cable and button contact at the same time with the soldering iron. As soon as the solder on the cable and button contact is liquid, bring the cable and the button contact together and wait until the solder has cooled and the button contact and the cable are soldered. At this point you can gently pull on the soldered cable and check whether it really holds. A correct soldered connection should under no circumstances come loose.
You repeat this for the second button contact and...
...the contacts of the remaining buttons.
Once you have finally soldered all the cables, the whole thing should look something like this.
Unfortunately you can't see it in the photo: Label the individual cables so that you'll know later which cable belongs to which button!
The cables for the individual buttons can then be routed through the holes in the speaker cover and the cover can be put on.
If the aperture is in the correct position, it can...
...can also be fixed directly with screws.
It looks something like this from above.
Once you have attached the cover, you can start combining one line of the double line of each button.
Since you will later have to solder the combined cable to the amplifier board, we recommend soldering a small, thin cable here. This makes soldering easier later.
Then everything should be covered with shrink tubing... isolated.
The prepared button connections will then look something like this.

Attach the connection panel on the back

Next is the preparation on the back of the speaker

If the speaker cable is firmly attached to your speaker, you can simply “clip” it off at the back. An electronics side cutter is perfect for this because it cuts the cable flush against the housing wall. Of course, any other side cutter will do the same.
It is almost impossible to see that a cable previously went into the housing.
You repeat the whole thing on the inside.
It's best to leave as much speaker cable as possible here, as this will have to be connected to the amplifier board later.
Now it's time to attach the cover for the rear connections. An on/off switch, the power connection and a terminal connection for an optional second speaker will later be housed here. The second channel of the stereo signal received via Bluetooth is output at this connection for a second speaker.
After you have aligned the connection panel correctly, you can start with the first mounting hole - as with the button panel before.
Then proceed in the same way as with the button panel. First drill a mounting hole and temporarily secure the cover from slipping with an inserted screw. Then the further holes are drilled. Before each drilling a new hole, check briefly whether the panel is still correctly aligned. So in the end everything is straight and fits together directly.
Once you have drilled all the holes and inserted the fastening screws (temporarily), the whole thing should look like this.
Now use a 3mm drill to pre-drill the rough position of the openings for the on/off switch, power connection and clamp connection.
You can use the pre-drilled holes after removing the connection panel...
...drill again with the flat milling drill. Make sure that you don't drill too big with the flat milling drill - that is, the hole will look out from under the connection panel.
Once all the holes have been drilled, you can check whether the drilled holes are big enough by placing the connection panel on it. In this picture you can see that some work still needs to be done because parts of the wooden back wall can still be seen in the hole for the clamp connection (rectangular hole on the right).
A bit of manual work is required here. So get to the file and file...
...until the cutouts in the speaker rear panel are large enough.
Before you can insert the terminal connection into the connection panel, it must... “pimped” a bit. The protruding collar has to be removed, otherwise the clamp would not fit through the hole in the speaker back wall. To do this, cut off the “collar” of the clamp connection using side cutters. Here you should definitely use a “real” side cutter and not an electronic side cutter. With the latter, if you use a lot of force, the “cutting jaws” can quickly break off or be damaged.
After processing, the collar is removed all around.
Now you can, in addition to the hollow socket for the power supply and the on/off switch...
…also insert the clamp connection.
So that you can solder the connections to the amplifier board later, you now have to prepare a few double cables. To do this, prepare three pieces of the double cable that are approximately 20cm long. You can also use the separated speaker cable for this.
Then insulate the ends of the cables by approx. 5-10mm.
To make soldering the contacts a little easier... now tin the contacts - like with the buttons before - with solder. At this point you can also tin the stripped ends of the cables.
This means that the individual cables can be soldered quickly again.
If you use a single-colored cable for the switch and the hollow socket, be sure to mark which cable is soldered to which connection. You will have to be able to understand later which line corresponds to the plus or minus pole.
Once you have soldered the cables, you can insert the connection panel into the back...
…and with screws…
As a small safety measure, it is practical to fix the contacts at this point with a little hot glue. This ensures that they cannot bend (due to soldering work, etc.) and possibly cause a short circuit.

Install TDA7492 amplifier board

Now that you've been preparing cables and connections all this time, it's finally time to connect these connections.

This is what the still “virgin” amplifier board looks like.
To make it easier to solder the individual connecting cables, all the required contacts are now tinned with solder. To do this, apply some solder to all circled contact surfaces. Make sure that the solder does not touch the silver housing of the respective button.
Two contacts must also be prepared on the power supply socket of the amplifier board.
So that you have both hands free during the following work and don't have to hold the amplifier board... should attach the amplifier board to a free space on the inside of the back wall. Here it was simply glued on with some hot glue.
Before gluing, make sure that the cables that come out everywhere also reach your amplifier board.
Before you solder the prepared cables to the amplifier board, you now have to solder the on/off switch to the hollow socket. To do this, solder the plus pole coming from the hollow socket to one of the lines of the on/off switch.
Insulate the soldered area again with...
...a small piece of shrink tubing.
You can now solder the free line coming from the on/off switch to the plus pole of the amplifier board as shown.
Close-up of the soldered plus pole.
You have to solder the remaining cable that comes from the hollow socket to the negative pole of the hollow socket.
Close-up of the soldered cables on the hollow socket of the amplifier board.
Now you can also connect the speaker cable of the terminal connection to the screw terminals of the amplifier board. It doesn't matter which screw connection you choose. However, you should make sure that the cable which is attached to the red terminal connection is also attached to the positive (+) screw terminal connection. The black terminal connection is therefore connected to the negative screw terminal connection.
Close-up of screw terminal connection.
Now prepare the connecting cable for the speaker. To do this, insulate the cable ends again by 5-10mm and...
...tin them with a little solder.
When connecting to the screw terminal, pay attention to the correct polarity of the speaker cable. You can see from the ground symbol next to “1” that this line is connected to the negative pole.
Close-up of the fully connected screw terminals.
Once you have connected all the cables (except for the buttons), the whole thing should look something like this. Now is the time for a first test. Connect the speakers to the crossover and test again before switching it on for the first time that you really haven't made a mistake with the polarity of the power supply hollow socket.
If the first test was successful, you can curl it up a little... lash together protruding cables.

Solder the button cables to the amplifier board

The final soldering task is to solder the prepared cables from the buttons to the buttons on the amplifier board.

Since you have already prepared the corresponding contacts, soldering the cables can be done quickly.
Make sure that no contacts are short-circuited with the silver button housing when soldering. First you should also solder the combined button cable to the ground contact. This is the place where the black cable is soldered in the picture.
If you test whether the amplifier board still starts every time after soldering on a new button cable, you can test whether the newly soldered button works. If a short circuit occurs between the contact and the silver key housing when soldering, the amplifier board will no longer start and you will immediately know which soldering point you need to rework.
…all of you then…
...button cable soldered on, the whole thing should look like this.
To protect the freshly soldered button cables from the mechanical stress during installation, you should coat the contacts/cables with hot glue.
Once you have soldered all the cables and tested the amplifier board and all connected buttons, the housing can now be closed again.

Close the back

Once you have tested everything, the back can of course now be closed. Make sure that you do not squeeze any cables and that the insulation wool in the speaker is in the correct position.

When screwing the back, make sure that you do not tighten the screws too tightly. Otherwise it can happen that they “pull” very deeply into the back.

Congratulations! You've breathed new life into your old speaker and built a cool new retro Bluetooth speaker.

Before commissioning, you should now follow the tips from the article Eektronik - Commissioning of a new circuit note.

Have fun with the project

I hope everything worked as described for you. If not or you have questions or suggestions please let me know in the comments. I will then add this to the article if necessary.
Ideas for new projects are always welcome. 🙂

PS Many of these projects - especially the hardware projects - cost a lot of time and money. Of course I do this because I enjoy it, but if you think it's cool that I share the information with you, I would be happy about a small donation to the coffee fund. 🙂

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