MINDANAO UNIVERSITY OF SCIENCE AND TECHNOLOGY

College of Engineering and Architecture

FET AUDIO MIXER AND PIEZO GUITAR AMPLIFIER

In Partial Fulfillment as a Requirement for ECE21(Electronics II)

Submitted by:

RONEL M. CULIBAR

Submitted to:

LLOYD JHON B. ESTAMPA, MSEcE

March 2015

I. PROJECT BACKGROUND AND DESCRIPTION

People tend to buy things individually to ensure its quality, however, this may cost them to spend more than buying things which has the same function and quality and built already in a single device. Majority of the people listen to music, which makes them buy things individually like audio amplifiers,ipod,etc. This project helps them to minimize the cost of buying expensive things individually and built a homemade device which has already what they need including an audio mixer, a guitar amplifier and a microphone circuitry.

An audio mixer is a device which allow us to mix multiple signals into one or more channel. Audio professionals nowadays used this to mix the sound of their devices (ex. loopstation, dj turntable,etc.). Because of its multiple input function you can create a mini band which uses only android phones.The mixer itself is drived by a Field Effect Transistor(2N3819) which combine the signals and transfer it to the Op Amp for further amplification. The Op Amp used in this project is the LM386 which is a low powered Operational Amplifier. With the combination of the two component, this gives us a clean powerful sound.

This device also include a guitar amplifier which uses Piezo Disk to sound the guitar and have its electric effect. This component is based on the vibrations and the force exerted to it that turns that energy to electrical energy. Aside from a guitar, you can also used this device to sound any other instruments like beatbox, violin and anything else that needs amplification.

Aside from an audio mixer and a guitar amplifier, this project also includes a microphone circuitry which enables user to sing while the mini band is playing. This device is good for person thatlove to sing and playing a guitar at the same time. If you don’t have these skills and listening to music is your favorite hobby, this is suitable for you as well.

Flow Diagram

The figure above shows the flow of this project. From the adaptor, the current flows to each component to power it and to make it operate. From these, you plug in the inputs whether a cellphone, guitar, microphone or all at the same time. After these, the inputted signals flow through the mixer. The signals flowing to it is combined and preamplified by the transistor. After it is mixed, it is transferred to the input of the amplifier to further amplify it. After this is done, the amplified signals are turned into sound by the loudspeaker.

Significance:

You can also create a mini band using your android phone and these apps. Just plug in your phone to the input plug and play the song you like.

Real Guitar

Real Drums

Real Bass

II. TRANSISTORS UTILIZED IN THE PROJECT

This FET is the heart of this project, without these, mixing wouldn’t be possible. Field-Effect Transistors (FETs) are unipolar devices, and have two big advantages over bipolar transistors: one is thatthey have a near-infinite input resistance and thus offer near infinite current and power gain; the other is that their switching action is not marred by charge-storage problems, and they thus outperform most bipolars in terms of digital switching speeds.The 2N3819 JFET in this circuit uses the self-bias configuration to provide greater amplification and thus, greater output. It takes signals from its Gate and is controlled by its Gate resistance to it’s Source which amplifies the input.

The 2N3904 is a common NPN bipolar junction transistor used for general purpose low-power amplifying or switching applications. It is a 200 mA, 40 volt, 625 milliwatt transistor with a transition frequency of 300MHz, with a minimum beta or current gain of 100 at a collector current of 10 mA. It is used in a variety of analog amplification and switching applications. The advantage of using this kind of transistor is its current gain which provide greater current for the LED to operate effectively.This is used in most switching applications especially flipflop circuit,etc.

III. CIRCUIT FLOW EXPLANATION

THE SCHEMATIC

The circuit starts after plugging in the 9v adaptor. The microphone circuitry is connected to one of its input, same with the piezo disk. The figure shown on the left is the schematic of the mixer only.

The schematic consist only of two inputs but you can add more inputs as long as you follow the setup and its connection. For my project, I created a 5 input mixer.

The green arrows signifies the flow of the input signals while the blue arrow signifies the current flow from the source. As the signals pass through C1 and C2 all DC offsets are blocked and only AC signals flow in this step. The potentiometer VR1,VR2 and the 100k-ohm resistors serves as the signal

control of the circuit which then controls the volume for each corresponding inputs. As the flow continue for each inputs, all the signals coming in are taken as one by the field effect transistor. Because of the FET’s almost infinite input impedance, these signals are preamplified as it pass through the transistor. The signal is then filtered by C3 which functioned same as C1 and C2.

The next stage is the amplifier part which needs idea on how to operate the LM386. The figure

on the left is the amplifier circuit. This circuit produces a gain of 200.

The signal enters the chip through pin 3 that is controlled by the 10k-ohm resistor, this serves as its volume control which allows signals to pass through.

Pin 6 is the chips voltage source pin while pin 4 is it’s ground pin. Pin 2 is the chips negative input gain while pin 3 is its positive input gain.

The op amp is considered to be a non inverting amplifier since the design provides a positive voltage gain. Pins 1 and 8 are the chips gain control. By putting a 10uF capacitor the gain will go up to 200 .

As the signal leaves through pin 5 which is the output pin,the 0.05uF and 10 ohm resistor, which serves as a Zobel Network filters the high frequency oscillations produce by the chip and the 220uF which filters the DC offset.

This is the microphone circuitry which is used to create sound from the microphone. The circuit uses an electret condenser microphone. This circuit is composed of a cascaded transistor circuit which both uses the fixed bias configuration. R1, R2, R3 is used to bias transistor Q1 while R5, R6 and R7 for transistor Q2. As the signals pass through C1 which blocks DC offset, transistor Q1 amplifies signal which is then transferred to Q2 but is controlled by 100k potentiometer and filtered by C2. The amplified signal exits at J2 which is then inputted to the mixer above.

Since we already know how the circuit works on each part, here is a little summary when the

circuits are combined.

From the piezo guitar amplifier circuit, the signal travels through input 1 of the mixer. As you connect sources to the other inputs you can adjust its volume by adjusting the potentiometers. You can also input the mic with the piezo and the other sources at the same time. This is applicable to all channels of the mixer. After the signals are mixed, the LM386 amplifier circuit receives all the input signals and turns it to audible sound.

This is a simple illustration on how the circuit works.

IV. PICTURES OF THE PROJECT

This is my testing stage in a breadboard. After that,

I layouted the board, etched it and soldered the components.(sorry for the quality.)

This is supposed to be my final case but I decided to change it and add additional 2 input to my mixer. The picture on the left has 3 inputs, the separated potentiometer is the amplifier volume control.

This is my microphone preamplifier circuitry but this is not finished yet. I put it on a universal PCB because I don’t have etching solution anymore.

This doesn’t have transistor Q2, the mic and the audio jacks yet but this is the right view of the circuit.

Bottom View

Using the same circuit that I etched. I changed the casing and this is the final output. I added sticker paper with different colors so that users will identify the volume control of each channel.

As you can see, i used the casing I supposed to use for

my mixer. This is my microphone preamplifier.

My speaker.

The Piezo Disk i used to power my guitar.

And this is me, having fun with my project. Also, I placed my piezo disk on my guitar.

My project, the audiomixer,the guitar amplifier and the microphone circuitry.

BILL OF MATERIALS

QUANTITY MATERIAL COST

6 Mono Potentiometers 78.0020 Resistors 7.006 Input Audio Jack(male) 90.004 Output Audio Jack(female) 60.001 4x5 CopperBoard 20.004 Mylar Capacitors 14.001 Ceramic Capacitors 1.008 Electrolytic Capacitors 24.001 2N3819 Transistor 20.002 2N3904 Transistor 7.001 LM386 IC 45.008 Stranded Wires(8meters) 40.004 Soldering Lead(4meters) 38.001 Piezo Disk 15.004 Shrinkable tube(4meters) 40.001 9V battery 25.001 Epoxy Clear 40.001 Sticker Paper 49.50

TOTAL COST

613.50

V. REFERENCES

http://www.aaroncake.net/circuits/mixer1.asp http://makezine.com/2011/12/20/collins-lab-diy-contact-mic/ http://makezine.com/projects/make-37/bass-bump-headphone-amp/

http://www.aaroncake.net/circuits/mixer2.asp http://www.learningaboutelectronics.com/Articles/How-to-build-your-own-audio-mixer http://www.electronics-tutorials.ws/transistor/tran_5.html http://en.wikipedia.org/wiki/Biasing