Category: Audio

XH-M548 Bluetooth Amplifier review

I recently bought this board for a personal project for my house. I thought it will be helpful for some folks out there that are planning to buy one. The board specs are impressive but you’ll be disappointed when you learn the actual figures. It turns out, those specs are just for marketing reasons.

The BAD things about this module

Wrong Output Power Claims

It claims 120W x 2 output power but in reality it only can handle 50W x 2 output max. Why? It only have 1 TPA3116 Amplifier chip on board which is only capable of delivering 50Wx2 power output. The large heatsink made me think that it have 2 TPA3116 chip but I was wrong. Looking at the bottom it will become obvious that it is only using 1 IC.

Aux input not Working

The aux input circuit is wrong. It is connected to the output of the op-amp which is a bad idea. Although this connector is not labelled “input”. But I know most of us will assume this is an Aux input as most bluetooth amplifier have. Based on the schematic, it will work as an Aux output rather than input.

Muting the Main Amplifier when no music is Playing

The bluetooth module is programmed to automatically mute the TPA3116 amplifier chip when nothing is playing on the bluetooth receiver or it is not paired. This is the reason why there is no audible hum even if I am touching the amplifier inputs.

Annoying Power on sound

It is not an issue if you are only using it with small speaker but it is very annoying for a 100W speaker. Or maybe its just me. The power on sound is a 3 note melody if I remember it right.

20W Audio Amplifier LM1875

LM1875 is an old yet reliable Audio amplifier IC. It is very common and you can get it for very cheap price. With this IC you can get up to 30W power output with 33V supply using 8 ohms speaker.

It has very simple circuit and very easy to build because it requires few components. This design is for single supply application. You can find more information about this IC on its Datasheet on this link.

PCB Design

This time around I am playing with Kicad. It’s is very different from what I used to but it has more feature and best of all its free! The layout is not yet optimized(i.e. size of the trace) because i am still learning. But you can download the project file so you can edit it for your own project. The size of the capacitors are just assumed.

3D render

The best about Kicad is that it has built-in 3D rendering feature for your board at no cost. This is a very useful tool for visualizing your project.

Downloads

You can download the Kicad project here:



Download page

 

Digital Audio Mixer Project with ADAU1701

It has been my long desire to design a digital audio mixer but there a too little resources regarding digital signal processing. While researching I stumble upon this little chip from analog which don’t require DSP knowledge. It is program using a software called sigma studio. There is no programming language, you just need to drag and drop modules. I am still on learning process, and this is just a test of what can I able to pack on a cheap ADAU1701 DSP. Considering the price of this DSP and the size of its memory, these modules that I was able to put was amazing.

What I was able to get with the limitation of ADAU1701:

  • 8 input channels
    • all have 3 parametric equalizer
    • all have compressor
    • all have volume control
    • all have 1 pre aux
    • all have 1 post aux
  • 4 output channels
    • 2 as main output with 6 band equalizer
    • 1 as pre Aux output
    • 1 as post Aux output

That’s about it. Adding more modules will prompt an error that you are out of memory. Considering what most 8 input analog mixer are offering on the market, this features are better. This project can be further improved so I have uploaded the project file on my download page so you can edit it yourself.

Sigma Studio Project

Main Schematic

Channel strip

These controls can be accessed through a microcontroller connected to it via I2C. The microcontroller can then be connected to user interface such as buttons and displays like LCD.

10 Channel variant

I have tried to use the maximum possible inout of the ADAU1701 which is 10 inputs but simplifying the schematic and removing the compressor on channel 7 and 8. The 2 additional channel can be used for bluetooth audio. I was able to achieve the following:

  • 10 input channels
    • Channels 1-6 has HPF, 3 band Parametric EQ, Compressor, 2 aux sends
    • Channels 7 and 8 has 3 band Parametric EQ and 2 aux sends
    • Channel 9 and 10 has 3 band EQ
  • 4 output channels
    • 2 main out with 10 band graphic EQ
    • 1 Pre Aux out
    • 1 Post Aux out

I think that is the best I can have for ADAU1701 DSP.

Multi-track Recording

This is the biggest challenge for this project, for now I don’t have any idea on how can it be done and how it can work with the ADAU1701. What’s clear for now is that the ADAU1701 DSP can’t be used for this purpose. I know it can be done using the XMOS chip but the development board is too expensive for me.

Conclusion:

The ADAU1701 is a powerful DSP for audio application. It can surely be used for digital audio mixer application with limited input channels. 8 channels maybe the most channels you can have for this application. You can have as much as 10 total inputs but you need to limit some functions like compressors to be able to use all the 10 inputs or else you will ran out of memory and the project will not compile at all.

Notes:

  • ADAU1701 only have 2 ADC channels build in, you need an external ADC to be able to add 6 more inputs.

I have yet to build the actual hardware but I am not sure when I can do it. When I got the fund and time for sure but I am not sure when.

Downloads:

Download page

Arduino Controlled Bass Mid Treble and input selector

My LC75341 project was a bit of a disappointment. It was working ok but it only offers bass and treble controls. The frequency response is not that good. It has very limited controls. I decided to stop that project because it is not what I am looking for. Now after lots of research, I stumble upon this digitally controlled bass mid treble IC from ST. What is great is that it has 7 band spectrum analyzer feature and a differential input. Plus it also has Q and frequency control and a subwoofer output. This is almost exactly what I want to do.

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2 Way Active Crossover with adjustable frequency

Most of the schematic design of active crossover on the internet are mostly with fixed crossover frequency. Here’s an interesting circuit that I found on Elliot Sound Products website. I learned a lot on this website when I was just a student. If you love to build sound products such as amplifiers and tone controls, you may already know about this website.

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Passive tone control circuit

If you are looking for a passive tone control for bass and treble control, here’s a simple one. Take note that because it is a passive circuit, it has no capability to boost signal. This circuit can only be used for high level source like car stereo speaker output. For headphone output, you may need to change some resistor values to decrease the attenuation of the signal. This will also modify the response of the circuit.

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