Category: Audio Processor

Build this Simple but amazing USB Audio interface for only $5

In case you want to connect your audio mixer or electronic piano or any other line level audio equipments to your computer or laptop for recording, here is a simple USB audio interface circuit that does the job. It is based of PCM29XX IC from TI. This is used in many analog audio mixers with usb interface such as the Behringer Xenyx USB mixer series.

About USB audio interface circuit

This circuit is USB powered. The IC has 16bit delta sigma ADC and DAC and capable of up to 48kHz sampling rate. it has stereo line level input and outputs.The crystal needed is 12MHz.

 

Quick PCB design

Here is a simple PCB layout that I designed using kicad software.

3D Render

simple usb audio interface PCB design
simple usb audio interface PCB design

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Prototype

Since I needed this circuit for my recording may piano and guitar covers, I built my own using universal PCB. This is what I used on my guitar and piano covers on my youtube channel here. 

At first time try, I am having problem with it. Windows shows an error message “Device not recognized” when I plug this to my Laptop’s USB port. Upon hours of troubleshooting, I found out that C13 and C14 is causing this issue. These are the capacitors connected to crystal oscillator. When I tried to removed these capacitors, the issue now gone. I tried to lower the value from 22pf to 15pf but it didn’t solve the issue. I also tried 5pf but same thing happens. For this prototype I just removed C13 and C14. Maybe because there is parasitic capacitance on the board that I used.

There’s no need for drivers, it installs automatically when you plug it in. It has 16bit ADC/DAC with up to 48kHz sampling which is good enough for recording. 16bit/48kHz might not sound great but it is actually good. This chip is used by Behringer on some of their Xenyx USB mixer and also on their cheap usb audio interface. The audio quality is not the best but it is better than those cheap USB sound card on the market. This is good enough for recording for you youtube content. 

Video

Here is the actual video of my prototype in action.

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USB audio interface Parts list

RefValuePart
C11u16V electrolytic capacitor
C20.1uceramic capacitor
C34.7u16V electrolytic capacitor
C44.7u16V electrolytic capacitor
C51u16V electrolytic capacitor
C61u16V electrolytic capacitor
C71u16V electrolytic capacitor
C81u16V electrolytic capacitor
C91u16V electrolytic capacitor
C101u16V electrolytic capacitor
C114.7u16V electrolytic capacitor
C124.7u16V electrolytic capacitor
C1322pceramic capacitor
C1422pceramic capacitor
D1LED:LED
J1USB_B:USB connector
J2Input3pin JST connector
J3output3pin JST connector
R12.2 ohmsResistor SMD or 1/4W or 1/8W
R21MResistor SMD or 1/4W or 1/8W
R31MResistor SMD or 1/4W or 1/8W
R41.5kResistor SMD or 1/4W or 1/8W
R522 ohmsResistor SMD or 1/4W or 1/8W
R622 ohmsResistor SMD or 1/4W or 1/8W
R71MResistor SMD or 1/4W or 1/8W
R81MResistor SMD or 1/4W or 1/8W
R91MResistor SMD or 1/4W or 1/8W
R10220 ohmsResistor SMD or 1/4W or 1/8W
U1PCM2902CUSB interface IC
X1CRYSTAL12MHz Crystal

The parts list does not include input and output connectors, you may opt to use RCA or phone jack connector.

I am planning to build an improve version of this device and sell it online so stay tuned! Subscribe to my youtube channel and facebook page to keep you updated! 🙂

Simple 2 way crossover project

Here’s a active 2 way simple crossover project for you.

About the circuit

The Circuit is simple and uses only 3 opamps per channel.

Crossover frequency is set around 234Hz. The cutoff(crossover) frequency can be changed for your requirement. The formula for the crossover frequency indicated below:

C4 is used to block DC voltage at the input. Since the input impedance of the circuit is very low, C4 value can be as low as 0.022uF. But for my final circuit I have used 0.1uF.

R3 and R4 are voltage divider used to provide half VDD voltage for the op amps. This is required because the power supply has no negative voltage. Without this, the output will be clip on negative cycle. C3 is just a filter capacitor to clean the voltage produced by the R3 and R4 divider. R5 is used to set the input of the input buffer to half VDD, 1Meg value is used so it will have little effect on the input impedance.

Simulation

Simulation result

As expected, the crossover frequency is around 234Hz.

PCB

For PCB design, I made it single layer so most of the DIYers can easily make their own PCB. As usual I used KiCad to design the PCB which is a free software. Resistors on the VDD are just jumpers(that is why it has value = 0).

J1 – Right input

J2 – Left input

J4 – Low Right output

J5 – Low Left output

J6 – High Right output

J7 – High Left output

J3 – Power Supply (12V – 24V)

3D Render

3D render using KiCad…

DOWNLOADS:

This project can be downloaded for you own personal use. If you want to use this for commercial use, please contact me on my Facebook page for licensing. 🙂

Please don’t forget to like my facebook page. 🙂

Download page

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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.

Continue reading “Arduino Controlled Bass Mid Treble and input selector”

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.

Continue reading “2 Way Active Crossover with adjustable frequency”

Arduino Controlled Bass Treble Volume and input Selector

Last time I have posted about how to control the LC75341 IC using arduino nano. And I also posted about how to modify the bass response of the LC75341 IC. This time I will be building a home amplifier for my TV, it will also feature a bluetooth reciever so that I can play via my phone.

Continue reading “Arduino Controlled Bass Treble Volume and input Selector”

LC75341 Bass response modifications

Last time I have a blog post regarding on how to control the LC75341 tone control using arduino. I never really tested the performance of that IC until recently I got time to play with it. My initial impression was not good. The bass sound seems very thin and I can’t get the “boomy bass” sound that I wanted. Maybe its just me but the bass sound is thin compared to my little JBL flip bluetooth speaker. By the the way, the kit was from E-Gizmo’s digitally controlled tone control. I have investigated and model the circuit of the LC75341 tone control for simulation and the simulation results confirm what I am hearing.

Continue reading “LC75341 Bass response modifications”