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Class D Switching Power Amplifiers and Power D/A conversion

First Bluetooth Speaker Build Tips
First Bluetooth Speaker Build Tips
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Old 11th September 2017, 10:53 PM   #1
bellamym is offline bellamym  United Kingdom
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Default First Bluetooth Speaker Build Tips

Hi All,

Sorry if this sounds stupid, but I'm brand new to all this and hoping for a little guidance in my first bluetooth speaker build. I've bought and listened to many bluetooth speakers but not found any that suit my needs so decided to look into building one and stumbled across this site.

My basic idea is to eventually (when i can figure out the electronics) is to build a speaker like this one:

Click the image to open in full size.
RCF HDK 20A

The speaker box will contain 2x10" bass/mid drivers and 2x Super tweeters.

Each speaker will require it's own amp channel of 300w max, so a total of 1200w max. I will be implementing a MiniDSP 2x4HD to split the audio signal into 4 channels to do the active cross over and all the extra fancy DSP tweaks and a bluetooth module for the audio input.

I've seen this amplifier board online:

Sure Electronics' webstore 2 x 500Watt Class D Audio Amplifier Board -IRS2092

I would require 2 of these boards.

Now the part where i'm stuck....power.

Can anyone recommend the best way to power these boards? I'm not sure if i require 2 transformers and rectifier boards or can use a large transformer into 2 rectifier boards and then into each amp.

Also...the MiniDSP board and Bluetooth module will require 12vdc...anyway i can step down the DC voltage to feed them from the same power source?

With this build weight may be an issue, i would like to try keep it under 30kg if possible and price for this speaker, under £1000.

I have no electrical safety experience, but don't be alarmed, i'm aware of the dangers and already have a friend who is ready to solder/wire/test all the components when i'm happy this will work

Thank you to anyone who can help me, and i'm open to any changes or better ways of doing this if it's even practical at all.

Thanks again

Mark (uk)
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Old 12th September 2017, 12:06 AM   #2
bellamym is offline bellamym  United Kingdom
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Default quick update...

So I've just found an artical produced by another member on this forum all about power supplies and how to build them, its a great source and answers many questions.

Building a Gainclone chip amp power supply.

So i will find a suitable toroidal transformer for the power i require (1200w) with dual outputs for 2 rectifier boards (making sure max Vdc does not exceed based on 250Vac input). Everything will be fused back to earth and fuse board for rectifier's added for safety.

The only other problems i have left are:

1) how to power my 12Vdc components. Another smaller toroidal transformer maybe, wired also into the same AC line as the other?

2) All of the electronics will be fixed to the back of my speaker inside which is wood....is this ok? The electronics wont be touching anything that sticks out the speaker, which make's earthing safer.

Thanks for any input guys. Once i'm more than happy this will work, i will start to buy the parts
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Old 13th September 2017, 09:22 AM   #3
bellamym is offline bellamym  United Kingdom
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So after more research and trying to work out the best way to start this project, i've found the following components that seem to be up for the job.

800w switch mode supply

SMPS - out puts 50v and a 12v for my other components

200w Amp Board X4

great low distortion amplifier boards

Power Supply Board

highly rated power supply board.

As i'm still learning, can anyone confirm if i need the power supply board or if it will help store the required power so the amps can do there job? and is it safe to take the 70vdc output from the SMPS and split it into 4, one to feed each board. The power supply is rated at 800w and 1200w max which matches the amp boards.


Thanks to anyone that can help with my crazy project
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Old 13th September 2017, 04:58 PM   #4
00940 is offline 00940  Belgium
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Location: Liège
A few starting points...

- what is the application for this project ? A PA system, a hifi one ?
- have you already chosen your drivers ? What kind of spl are you after ? That will define the power you need.
- why two tweeters ? Is it supposed to be a pseudo stereo speaker or a single channel one ?
- the amps are ok but you have to pay attention to the fact that they're only suitable for 8ohms speakers, not for 4ohms ones.
- maybe have a look at this supply if you want something more reliable than the average ebay stuff: SMPS800RE +-72V 230V Power supply
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Ben.
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Old 14th September 2017, 06:54 PM   #5
bellamym is offline bellamym  United Kingdom
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Hi Ben,

The idea is to build a bluetooth speaker that is a cross between PA and Hifi.

The whole idea started 2 weeks ago, i own 2 bluetooth speakers. I own a bose sound link mini and a JBL xtreme. Both sound very nice, have great low end but lack SPL. After trying to find a bluetooth speaker with higher spl, i came across normal Active PA speakers with built in bluetooth etc but again, they lack sound quality.

i had a look at Sony's GTK-XB7 and also LG's FH6, both quite powerful bluetooth systems, but sound muddy :/ so i decided to build my own

I have NO electrical experience so thought this would be a good project to learn along the way though a friend who is electrical qualified will help with the build and all testing as he works with mains electrics so has all the safety knowledge so i don't blow me or anything else up.

So this is what i'm after.....

A bluetooth speaker, that sounds great at all levels and has plenty of power (none of this false 200w crap you normally get written on systems) and has highs over the 20khz and also plays down as low as i can. I understand the box design will be the limiting factor for the lows, but will still buy speakers capable of 20-30hz at the bottom end.

I plan to run each speaker of it's own dedicated amp and have it's own signal from a MiniDSP 2x4HD. This should give each speaker the power it wants and make tuning the cross over easier as it will be active.

The miniDSP also (with a microphone) can do room tuning and will allow me to run any kind of eq i want, so i could for instance, cut the lows 60hz and down so i can gain extra spl for outdoors if required.

I plan on running 2 tweeters simply because i'm after stereo sound though i know it won't be as good as speaker positioned further apart, but this is the trade off for running one speaker box.

I plan to keep updating this project by adding lights, maybe Lazer effects into the box as well.

I was originally going to use 4Ohm amps but found by running 8ohms i got a much better selection of speakers as most seem to be this way.

I will take a look at the power supply you have linked too just in case the one i ordered above is no good.

again, if this fail's it fails. It more of a learning project with the hope something great comes out of it at the end
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Old 16th September 2017, 10:55 PM   #6
Pygmy is offline Pygmy  Netherlands
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Location: Haarlem
I don't want to be "that guy" but I do feel it has to be mentioned that using Bluetooth inherently means your audio data is being compressed and will suffer in audio quality....
So if your aim is to get the best possible audio quality, don't use Bluetooth.
If not, forget I ever mentioned this.
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Old 17th September 2017, 01:42 PM   #7
bellamym is offline bellamym  United Kingdom
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Hi Pygmy,

I understand bluetooth will unfortunately impact the sound I've seen and heard this with many other bluetooth speakers including car head units. The MiniDSP board i will be using will accept USB Digital input from a computer, so i do have that option if i want to get the best signal in and best audio out, and i will use this for at home listening but for a quick and easy garden party, bluetooth quality should do quite fine Thank you for your advice though!! I'm not even sure how this project will sound, but it's all trial and error
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