# Portable Bluetooth Speaker

#### BrusselSproot

##### New Member
Hey there forum users!

I’m having problems trying to circuit together my speaker

I have spent months researching everything I need to do and what I need to buy, everything arrived I have built my wooden case for the speaker and now I’m creating the circuit.

I have created the circuit and my battery will have a red light when switched on and no light when switched off, the on/off switched I have soldered it to when is turned on, the red light on the battery turns off and when the on/off switch is turned off, the red light is on, I’m sure this means it is working? The rest of the circuit is still not powered by the battery, I’m trying to figure out what I have done wrong and what needs fixed, any help would be excellent!

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#### dr pepper

##### Well-Known Member
Welcome.
If the light is on when the speaker is off, and off when the speaker is on you have the contact connections the wrong way round.
You need to be sure of the connections, if you short the battery it'll go into melt down.

#### BrusselSproot

##### New Member

I’m confident my wiring is in the correct position for the rest of the circuit my only confusion is with the on and off switch, it has 3 prongs and I’ve connected the power supply’s black wire to (1) prong which is ground and the red wire to (3) the outputs black wire is connected to prong (1) to (-) on the boost converter and red is connected to prong (2) to (+) on the boost converter

I had to buy a new switch and it only supports 12v would this affect the battery when it puts out 10.8 - 12.6v?

Sorry if my circuit terminology isn’t great

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#### Gamma Ray

##### New Member
Hi,
You really need to use a multimeter on the ohms scale to figure-out the switch connections. The voltage rating of the switch should be OK. However, your audio amp is rated 160W+160W. Is your boost converter step up volt regulator capable of supplying the required high currents? If you are going to use these high currents, then your switch will probably not last very long.

#### BrusselSproot

##### New Member
Thanks for the message gamma,

I will buy a multimeter and take a look at this, been working on this project for a while and would be a shame to see it not work with the money put in to it.

I’ll update you with a reply soon, thank you

#### audioguru

##### Well-Known Member
Since the switch wiring shows a GND terminal then doesn't the switch have an LED inside it? Does its LED work properly?

Your Bluetooth decoder board says "12V" but your wiring is feeding it the boosted voltage that will blow it up.

I am amazed that the cheap amplifier module even has an automatic fan on it.

The TDA7498E amplifier IC is rated at 85% efficiency so when the outputs are blasting severely distorted 320W then the heating will be 55W. Then the total 375W at 36V results in a current from the output of the boost converter of 10.4A. C an the boost converter produce 36V at 10.4A?
The boost converter might have an efficiency of 90% then its total input power is 415W. Then the 12V current through the switch and from the battery is 415W/12V= 34.6A!! Can the switch and battery survive that much current?

#### BrusselSproot

##### New Member
Hey audioguru!

The switch LED wasn’t lighting up when I turned the battery’s power on and I showed an electrician tutor at my college the diagram sheet and they said the Bluetooth decoder would be ok going through the boost converter, but they were probally wrong, i just agreed with what they said.

I watched videos on YouTube of people building Bluetooth speakers and I was trying to build something louder and better, I thought all of these parts would work together but maybe not?

What parts would you say need swapped to power the speakers and the amp as these were both the most appealing to the project I desired

#### audioguru

##### Well-Known Member
I wonder if the LED in the switch needs an external current-limiting resistor, or if it already has it inside.

Do you need such high power?
If the amplifier uses a 36V supply then its total sound power output is 320W with 10% awful distortion, or 250W with 1% noticeable distortion, or 200W with low inaudible distortion. That is loud enough to deafen anybody within 10 meters away from the speakers.

Please post a link to specifications of the switch, battery and the voltage boost converter so we can see if they will survive the 34.6 amps of current.

Have you considered using a single 20,000mAh (or smaller) 12.6V battery without a boost converter then the output power will be 13W per channel like from a normal modern car radio, then your hearing and the battery charge will last for a long time.

#### BrusselSproot

##### New Member
I was going to play the speakers at nothing above 120 watts so 100 watts would be good enough

Battery: https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/142944397285

Switch: https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/261513977084

Boost converter: https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/182177792880

Hopefully the description of the products in the links will have enough information

I chose this battery thinking the battery life would last longer but if I should use another battery to make this project work then that’ll be fine thank you guru!

#### audioguru

##### Well-Known Member
Didn't you read the spec's for the cheap Chinese junk from ebay?

How will you limit the current to the small amount the parts are rated for?
The cheap battery is rated for an output of only 1A to 2A so the 34.6A will explode it. You need a portable battery that is used to jump-start a car.
The cheap switch is rated for AC then the high current DC will probably weld the contacts together if it is switched when the sound output level is high.
The cheap boost converter has a 4A maximum input current so the 34.6A will also explode it.
I wonder if the cheap amplifier is built properly.

If you use a higher current battery and switch rated for 4A DC then the boost converter can be turned down to about 15V then the maximum current from the battery and into the boost converter will be 4A. The amplifier output will be about 23W per channel at 1% distortion.

I have seen guys with a portable high power sound system for a party in the park. It uses a huge car battery and a high power car amplifier that has a boost converter built into the amplifier.

#### BrusselSproot

##### New Member
I didn’t realise these parts wouldn’t work together, it’s good you have told me that there was a risk with these parts.

I’m trying to create something small enough to carry around and loud enough to enjoy, this project would of fit in my bag but if these parts don’t work together I shall try find new parts, do you think i could continue this project and still have what I’m looking for, it being small enough to carry, and 80-120 watts? No noticeable distortion

I wouldn’t mind buying new parts but the less the better, would everything from the boost converter to the speakers work, I just need to find a battery and a switch that will also function in this circuit

#### audioguru

##### Well-Known Member
I heard a Bose portable Bluetooth speaker in a store and it sounded great. It was small and lightweight, selling for $299US. Chinese copies selling for$49US sound fairly good. Their output power is 3W per channel. They are fairly loud.