I recently got my hands on a Fosi Audio BT20A Pro Bluetooth amplifier to replace my old vintage integrated amp. Initially, I didn’t expect much with this little amp regarding its compact size and its price tag, but its sound quality and convenience of on board Bluetooth connection quickly won me over.
However, the bundled 32V power supply left something to be desired. I had to turn the volume to 12 o’clock to achieve the same room-filling sound that my old 65W integrated amp delivered at 9 o’clock.
After some research, I discovered that using a higher voltage power supply could significantly improve performance. The BT20A Pro can accept a wide range of inputs from 24V to 48V.
Since I’ve second-hand MEAN WELL SE-450-48 (48V, 9.4A – 450W) power supply lying around, I decided to give it a try. The results were promising, but I noticed a significant increase in the amplifier’s temperature. The aluminum shell became uncomfortably hot to the touch.
I found many users reporting this issue, but I was still doubtful because I was using a non-official power supply. I contacted Fosi Audio support, and they reassured me that this was normal when using a 48V power supply.
It is normal. This model does not have a sleep mode, so it remains in standby, especially when using 48V, which can generate heat. The BT20A PRO operating at 36°C is within the normal temperature range, and it is expected to generate some heat when powered on. When paired with a 48V power supply, the temperature may increase by approximately 5°C compared to when paired with a 32V supply. To help with cooling, it is recommended to use a fan and position the amplifier vertically.
Reply from Fosi Audio Customer Support
One advantage of an external power supply is the ability to adjust the voltage. So I turn the voltage down and settled on 42V, which brought the temperature down to an acceptable level while still providing ample power. I could now achieve room-filling sound with the volume set around 10 o’clock.
The Power Supply Enclosure Design
After testing it for several days and being satisfied with the results, it was time to make the setup more permanent. To ensure safety and convenience, I decided to put everything in an enclosure. I started by listing all the requirements for the input/output, connector types, and other essential features.
For the AC input, I chose an IEC320 C14 male socket with a fuse and switch. These IEC sockets are widely used in HiFi systems, allowing me to easily switch power cords and providing access to a large collection of high-quality components for DIY upgrades.
Additionally, I needed an extra port for lower voltage output to use with other devices, so I integrated a step-down converter and couple of small voltmeters to monitor the output voltage.
Printing an entire case for the large SE-450 wasn’t feasible, so I looked for alternatives and found a 160x80x300 aluminum extrusion case that fits the power supply and all the peripherals perfectly.
To enhance the design and make it more convenience to use, I’ve added several 3D-printed components and extra parts for easy integration of additional peripherals.
The overall look was inspired by studio lighting power packs, giving it a sleek and industrial appearance.
The 160×80 aluminum extrusion cases come in various lengths, ranging from 170mm to 450mm.
If you prefer to use a smaller power supply, the 3D printed parts should still fit perfectly.
Just make sure to select a case that is 4-6cm longer than total length of your power supply to leave enough room for the connectors and wiring.
About Aluminum Enclosure
To save space, I designed the enclosure to be used vertically. All the electronic connectors can be easily accessible from the top.
I’ve design a 3D-printed mount plate with slots for each components instead of cutting a hole in the original metal plate. This makes it easier to mount small components and adjust the connector layout if needed.
To make It look like studio power pack I’ve added dual handles for easy transport and protective feet to protect the soft aluminum case and the floor.
While this power supply may appear oversized for this small amplifier, it perfectly meets my needs since I already have the PSU and can share it with additional devices in future upgrades.
WARNING: This project involves working with AC power, which can be dangerous and potentially lethal if proper safety precautions are not taken. Please ensure that you have a solid understanding of electrical safety before attempting this project. If you are unsure or uncomfortable working with AC power, please seek the assistance of a qualified electrician. Always disconnect the power source and discharge any capacitors before working on any electrical circuit. Failure to take appropriate safety measures can result in serious injury or death.
Making the Power Supply
Below is the wiring diagram for assembling the enclosure:
AC Input: Connect the IEC320 C14 socket to the power supply using 14AWG (2.5 Sq.mm) wires with spade connectors.
DC Output: I’ve use 16 AWG wires to connect main DC output including GX16 connector, 5.5mm barrel connector (5.5×2.1 or 5.5×2.5 depend on your application) and the step-down converter.
IEC320 C14 Socket (with Fuse and Switch)
There are many variation of this similar socket. The one with replaceable switch generally have 5 to 7 pins. (3 pins for AC, 2 to 4 pin for the switch depend on switch type). There’re also have 3 pins version the switch is integrated to the socket so the jumper wire in not necessary. However the switch will not replaceable.
The IEC320 Socket I have included 6 pins, it need extra wires to connect from the AC input to the switch.
The pin for neutral wire, which require for the switch with indicator light, is usually distinguished by its gold color.
This pin should not have connectivity to any other pin, whether the switch is on or off. I strongly recommend double-checking pin connections with a multimeter.
I used 2.5 Sq.mm wires crimped with spade connectors to connect to the IEC socket’s pins. On the other end, I used Y-type spade connectors to connect to the screw terminals on the power supply.
Additionally, you will need a 5x20mm fuse, which is usually not included with the socket. I used a 10A fuse for this power supply.
GX-16 Connector and 5.5 mm DC Jack
The GX-16 connecter are widely use in audio equipment. It’s known for their high level of reliability and durability. It’s provide a secure and stable connection with a build-in locking mechanism while it easy to connect and disconnect.
Each pin is labeled by number, so it’s important to match the wiring to each pin on both the male and female connectors. For 2-pin DC connectors, Pin 1 is usually V+ and Pin 2 is V-.
The DC input connector for the BT20A Pro amplifier is a 5.5×2.5mm barrel jack, with the inner pole being V+. If you’re using a pre-made cable, it’s a good idea to check the polarity of each pin before connecting it to the amplifier to avoid any potential issues.
DC Step-Down Converter
I use 5A variable step-down converter which accept 10-110v dc input. It’s include potentiometer to adjust output voltage from 2 to 34v at maximum 5A. I recommend to tuning the output voltage before connect it to the voltmeter which accept maximum input at 30V.
5A Step-Down Converter with 3D-Print Mount Plate
Output Rating:
2-20V=5A
20-28V= 2.5A
28V-34V= 2A
To power the step-down module, I’ll use 18 AWG wires. I’ll solder one end to the module’s input soldering pads and crimp the other end with a Y-spade connector for the power supply’s screw terminal.
For the output, I’ll use 2 pins plastic terminal to connect between the module’s output and 5.5mm dc jack. This make it easier to detach the connections when removing the connector mount plate from enclosure, ensuring convenient maintenance and assembly.
Automotive Plastic Connector Terminal
To ensure safety, it’s important to use female terminals for the wires from the step-down module. Unlike the male side, the female terminal have walls between each pin, preventing contact and minimizing the risk of short circuits if the terminal is disconnected while the power supply is still powered. This precaution ensures safety and prevents potential damage to the components.
To mount the step-down module to the enclosure, I designed a custom 3D print mounting plate. The step-down module will mount to the plate with M3x6 screws.
This plate will attaches to the side of the power supply using power supply’s M4 mounting hole. Use M4x10 screws to secure the plate to the power supply.
I designed the lower mounting holes of the mount plate as open-end slots. Once the power supply is attached to the enclosure with VHB tape, it becomes very difficult to access the lower screws if you need to remove the step-down module. With the open-end slotted holes, you can simply remove the top screw and slide the plate up to detach the step-down module easily.
Please note that I have not tested its output with any audio devices yet, so I am not certain if it is suitable for audio equipment. This converter is the only one I currently have that can accept up to 48V input. Most of small buck converter are accept only 35V. So please carefully check the specification, if you use different step down module.
The step-down converter with the variable voltage I used in this project seems to be discontinued. The only available option now is a 5A step-down converter with fixed outputs voltage (5V/9V/12V/24V). However, It has a higher rating with a 24V output. The mount plate for it also available in the download link.
About Step Down Converter
0.28″ DC voltmeter
I’ll be using a 3-wire 0.28 inch LED voltmeter. With the separate signal wire it can measure up to 100V. However, it accepts a maximum input of only 30V, so be careful not to connect it directly to the 48V power supply.
To powering it up, I will connect both voltmeter input wires (red and black) to the output from the step-down converter.
For measuring the voltage from power supply you can connect the signal wire (yellow) from the voltmeter directly to the V+ on the power supply.
To measure the voltage output from the step-down converter, you can remove the signal wire (yellow) and bridge the its pin to the V+ pin (red wire). This will directly measure voltmeter input voltage and help reduce wire clutter.
To mount the voltmeter to the mount plate, I used M2x6 self-tapping screws. The voltmeter can be mounted upside down depending on your preference.
On the back of the voltmeter, there is a potentiometer for adjust the measured voltage. After completing all the wiring, you can calibrate it using a multimeter. I found both LEDs measured around 0.7 to 1 volt lower compared to my multimeter.
Assembly the Enclosure
160x80x220 Aluminum Case
The 160×80 aluminum enclosure is a split-type, with the main case divided into two halves. Each half has tongue and groove joints to keep proper alignment when assembled. Both sides are secured with front and back metal plates and M3 screws.
To attach the power supply to the enclosure, I’ll using 3M VHB double side tape and attached it to one side of the enclosure. I prefer using VHB tape because I want to avoid drilling holes in the aluminum enclosure, and VHB tape offers a secure and convenient alternative.
After connecting all the wires to the power supply and attaching the step-down module to the side, close the another half of enclosure case and secure them to the bottom metal plate with the provided M3 screws.
Next, I’ll align the connector mount plate in place and attached both handles to each side of the enclosure. Secure the handles to the enclosure with M3x12 button head screws through the provided mount holes on connector plate.
Due to the positioning of the screw holes, which are partially blocked by the handles, a #2 ball head Allen wrench will make this part a lot easier.
For the protective feet, it should fit tightly into the bottom part of the enclosure. Simply push them into place.
Additionally, I’ve provided M3 mounting holes, so if you prefer, you can replace the original M3 screws with longer countersunk screws to secure the feet and the metal plate with the enclosure.
Conclusion
Building the custom enclosure for my power supply has been quite the journey. I’ve been looking for solutions and designing enclosures for external power supplies to use in many application. Making the fully enclosed designs with 3D printer were often a hassle with large, long prints.
But with the aluminum case. It saved me from printing large parts, made assembly straightforward, and still maintained a sleek, industrial look. Fully enclosing everything ensured it was both safe and convenient to use.
This enclosure enhancing both functionality and aesthetics in my setup. I can tailored the setup to meet my specific needs for powering audio equipment and other devices. With the custom 3D print connector mount plate, it ready for whatever upgrades I throw at it in the future.
This is my first power supply enclosure made for an audio amplifier. I’ve plan to add a Box X4 Phono Preamp to my setup. It needs a 12V 1.5A input, so this power supply should handle it just fine. Plus, the GX-16 connector lets me experiment with fancy custom-made DC cables.
This project proves that with a little creativity and some elbow grease, you can turn a basic setup into something custom-made, totally awesome and making tech work better without breaking the bank. Whether you’re a tinkerer or just looking to personalize your gear, DIY projects like this one are definitely worth the effort.
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