Table of ContentsMixing Console................................................................................................................................2

Introduction...........................................................................................................................2Structure.................................................................................................................................2Applications............................................................................................................................3Mixing console manufacturers.............................................................................................3

Abstract...........................................................................................................................................5Schematic........................................................................................................................................6Board Assembly..............................................................................................................................7Operation........................................................................................................................................8Printed Circuit Board Layout........................................................................................................13

Eagle CAD Design Rules.......................................................................................................14Copper Bottom Layer..........................................................................................................15PCB Assembly Diagram.......................................................................................................16

SPICE Simulation...........................................................................................................................17Analysis Screen-shots...................................................................................................................18SPICE Net-list.................................................................................................................................19SPICE Plot Export – AC analysis...................................................................................................20Operational Amplifier – TL071 SPICE model...............................................................................22SPICE Analysis Graphs..................................................................................................................23

AC Frequency analysis.........................................................................................................23Transient Analysis Graphs...................................................................................................24

Troubleshooting............................................................................................................................26Bill of Materials.............................................................................................................................27Conclusion.....................................................................................................................................28Project Pictures.............................................................................................................................29Bibliography..................................................................................................................................30

Mixing Console

IntroductionIn professional audio, a mixing console, or audio mixer, also called a sound board, soundboard, mixing desk, or mixer is an electronic device for combining (also called "mixing"), routing, and changing the level, timbre and/or dynamics of audio signals. A mixer can mix analog or digital signals, depending on the type of mixer. The modified signals (voltages or digital samples) are summed to produce the combined output signals.

Mixing consoles are used in many applications, including recording studios, public address systems, sound reinforcement systems, broadcasting, television, and film post-production. An example of a simple application would be to enable the signals that originated from two separate microphones (each being used by vocalists singing a duet, perhaps) to be heard through one set of speakers simultaneously. When used for live performances, the signal produced by the mixer will usually be sent directly to an amplifier, unless that particular mixer is "powered" or it is being connected to powered speakers.

StructureA typical analog mixing board has three sections:

• Channel inputs• Master controls• Audio level metering

The channel inputs are replicated monaural or stereo input channels with pre-amp controls, channel fader and pan, effects and equalization controls. The master control section has level, tone, amplification and auxiliary return level controls. In addition it may have solo monitoring controls, a stage talk-back microphone control, muting controls and an output matrix mixer. Audio level meters may be provided above the input and master sections or they may be integrated into the unit (if present).

Illustration 1: Professional Mixer

ApplicationsDub producers/engineers such as Lee "Scratch" Perry were perhaps the first musicians to use a mixing board as a musical instrument. Public address systems will use a mixing console to set microphones for different speakers to the correct level, and can add in recorded sounds into the mix. A major requirement is to minimize audio feedback. Most bands will use a mixing console to combine musical instruments and vocals to the correct level. Radio broadcasts use a mixing desk to select audio from different sources, such as CD players, telephones, remote feeds, or prerecorded advertisements. Noise music musicians such as Merzbow or Wolf Eyes may create feedback loops within mixers, creating an instrument known as a no-input mixer. The tones generated from a no-input mixer are created by connecting an output of the mixer into an input channel and manipulating the pitch with the mixer's dials.

Mixing console manufacturersSome of the most popular mixing console manufacturers are listed below:

• Roland Corporation• Soundcraft• Shure• Yamaha Pro Audio• Behringer

Commercial mixing modules run into thousands of dollars and have many advanced features like mechanized fades, pitch shift, equalization, automatic leveling, LFO envelop generation, independent frequency synthesis and arpegiators.

Some specifications of Yahama Corporation's top mixing station, DM2000VCM, are listed below:

• 96-input 22-bus Mix Capacity at 96 kHz• Precise 24-bit/96-kHz Audio• 24 microphone/line inputs with balanced XLR/TRS jacks• Versatile MIDI control capability is provided via MIDI IN, OUT, and THRU

connectors and an independent MTC input connector.• USB and RS422 "TO HOST" connectors, an XLR type SMPTE time code input.

Illustration 2: Controls and LFO envelope [DM2000]

Illustration 3: Mixing Curves Display [DM2000]

Abstract

Research Focus

The project we have undertaken, aims to design and construct a basic analog audio mixer. We have attempted to design a mixer using low-cost components and passive mixing techniques: whose actions and performance would be comparable to a basic commercial module. The mixer is designed to be fairly tolerant to supply and other external parameters which are inherently introduced due to interfacing with external components.

Issue(s) Addressed

The major issues faced in the construction of the project can be broadly bifurcated as: design considerations and construction limitations.A balance between performance and cost was to be struck, which was the determining factor in choice of operational amplifier. Typically low cost operational amplifiers suffer from noise degradation during rail to rail performance. The input impedance is also considerable. Hence a high input impedance operational amplifier with good near-rail performance was chosen. The standard 3.5mm input connector was chosen due to its popularity in audio circuits and easy availability. Converters for this jack are also easily available. These were the major considerations in the design stage. For the construction, It was our aim to keep the circuit fairly well spaced for easy manufacture and verification. So 16 thou tracks were chosen with with 18 thou clearances. These values were determined experimentally and observed to lend themselves to good repeatability and accurate manufacture. These also sufficed for our space constraints, and were thus chosen.

Research Methods

Parameters for design were determined experimentally, through construction on the solder-less breadboard and through simulation in Spice software. Limitations for the manufacture, was determined by etching and constructing other small circuits in progressively finer tolerances till the optimum values between area of board and ease of manufacture was not obtained. These, as mentioned above are found to be: 16 thou tracks with 18 thou clearances.The layout of the PCB was prepared in board layout tool 'Eagle CAD' by Cadsoft. Simulation was conducted on 'Ltspice' by Linear Technologies.

Conclusions and Recommendations

We find that by using the components described herewith, it is possible to manufacture a low cost, practical mixing solution, whose performance matches commercially available modules.Further, we have determined that for easy and accurate manufacture the track width should be atleast 16 thou and clearance should be at-least 18 thou. Drill size of 0.6 mm is suitable for all components save the 3.5 mm female TRS connector, which require a 1.1 mm drill.

Schematic

Board Assembly

OperationAt the heart of the circuit is the TL071P operational amplifier.

The JFET-input operational amplifiers in the TL07x series are similar to the TL08x series, with low input bias and offset currents and fast slew rate. The low harmonic distortion and low noise make the TL07x series ideally suited for high-fidelity and audio preamplifier applications. Each amplifier features JFET inputs (for high input impedance) coupled with bipolar output stages integrated on a single monolithic chip.

Some features of the TL071 operational amplifier that warranted its choice include:

• Low Power Consumption

• Wide Common-Mode and Differential

• Voltage Ranges

• Low Input Bias and Offset Currents

• Output Short-Circuit Protection

• Low Total Harmonic Distortion - 0.003% Typ

• Low Noise

• Vn = 18 nV/√Hz Typically at f = 1 kHz

• High Input Impedance . . . JFET Input Stage

• Internal Frequency Compensation

• Latch-Up-Free Operation

• High Slew Rate - 13 V/µs Typical

• Common-Mode Input Voltage Range

• Includes VCC+

The pin-outs of Tl071 are as follows:

Illustration 4: Pin Configuration of Tl071

The typical response of the TL071 operational amplifier is shown below. Low peak overshoot and quick damping make it suitable for use in audio circuits. This response is favorable for linear mixing.

Illustration 5: Typical response of TL072

Operational Amplifier

The input stage is a differential amplifier. The differential amplifier used as an input stage provides differential inputs and a frequency response down to d/c. Special techniques are used to provide the high input impedance necessary for the operational amplifier. The second stage is a high-gain voltage amplifier.This stage may be made from several transistors to provide high gain. A typical operational amplifier could have a voltage gain of 200,000. Most of this gain comes from the voltage amplifier stage. The final stage of the OP AMP is an output amplifier. The output amplifier provides low output impedance. The actual circuit used could be an emitter follower. The output stage should allow the operational amplifier to deliver several mili-amperes to a load.Notice that the operational amplifier has a positive power supply (+Vss) and a negative power supply (- Vdd). This arrangement enables the operational amplifier to produce either a positive or a negative output. The two input terminals are labeled "inverting input" (-) and "non-inverting input" (+). The operational amplifier can be used with three different input conditions (modes). With differential inputs (first mode), both input terminals are used and two input signals which are 180 degrees out of phase with each other are used. This produces an output signal that is in phase with the signal on the non-inverting input. If the non-inverting input is grounded and a signal is applied to the inverting input (second mode), the output signal will be 180 degrees out of phase with the input signal (and one-half the amplitude of the first mode output). If the inverting input is grounded and a signal is applied to the non-inverting input (third mode), the output signal will be in phase with the input signal (and one-half the amplitude of the first mode output).

Summing and Mixing Operation

The Summing Amplifier is a very flexible circuit based upon the standard Inverting Operational Amplifier configuration.

Illustration 6: Block Diagram of Operational Amplifier

The summing action of this circuit is easy to understand if you keep in mind the main "mission" of the op amp. It's a simple one: keep the potential of the negative terminal very close to the positive terminal. In this case, keep the negative terminal close to 0V (virtual ground). The op amp essentially nails one leg of R1, R2 and R3 to a 0V potential. This makes it easy to write the currents in these resistors.Consider the inverting configuration of an operational amplifier. If we add another input resistor equal in value to the original input resistor, Rin we end up with other operational amplifier circuit called a Summing Amplifier, "Summing Inverter" or even a "Voltage Adder" circuit as shown below.The output voltage, (Vout) now becomes proportional to the sum of the input voltages, V1, V2, V3 etc. Then we can modify the original equation for the inverting amplifier to take account of these new inputs thus:If,

I = I1 + I2 + I3 = - (V1/Rin + V2/Rin + V3/Rin )

then,

Vout = - { (Rf/Rin) V1 + (Rf/Rin) V2 + (Rf/Rin) V3 }

However, if all the input impedances, (Rin) are equal in value the final equation for the output voltage is given as:

Vout = - Rf/Rin ( V1 + V2 + V3 + ....VN)

We now have an operational amplifier circuit that will amplify each individual input voltage and produce an output voltage signal that is proportional to the algebraic "SUM" of the three individual input voltages V1, V2 and V3. We can also add more inputs if required as each individual input "see's" their respective resistance, Rin as the only input impedance. This is because the input signals are effectively isolated from each other by the "virtual earth" node at the inverting input of the op-amp. A direct voltage addition can also be obtained when all the resistances are of equal value and Rf is

Illustration 7: Summing Amplifier

equal to Rin. A Scaling Summing Amplifier can be made if the individual input resistors are not equal. The resistances would then modify to:

Vout = -Rf {(V1/R1) + (V2/R2) + (V3/R3) }

The Summing Amplifier is a very flexible circuit indeed, enabling us to effectively "Add" or "Sum" together several individual input signals. If the inputs resistors, R1, R2, R3 etc, are all equal a unity gain inverting adder can be made. However, if the input resistors are of different values a "scaling summing amplifier" is produced which gives a weighted sum of the input signals.

This is the fundamental concept behind the Audio Mixer. The diagram below illustrates this.

Illustration 8: Fundamental of Operation

Printed Circuit Board LayoutThe printed circuit board was designed using Cadsoft's “Eagle Cad” software. The name EAGLE is an acronym, which stands for 'Easily Applicable Graphical Layout Editor'. It consists of a schematic entry software, a layout editor and design rules checker.

The schematic was laid down in the schematic editor. Operational amplifier footprint was sourced from the library 'Linear' by Linear Devices Inc. The 3.5 mm TRS connector was sourced from the library 'Conn-Hiershmann' by Hiershmann Connectors. All footprints were checked for dimensional accuracy.

The design rules were modified to suit the limitations of manual manufacture. A summary of the design rules are as follows:

• Minimum track width: 16 thou

• Minimum Clearance: 24 thou

• Routing grid: 50 thou

• Minimum Drill: 8 thou

• Restring: 20 thou

The design was exported to a image with the settings: DPI = 300, Mirror = False, Monochrome = True. This image was subsequently printed and used for manufacture. The image is the top view of 'Copper Bottom Layer' looking through the board.

The complete 'Design Rules File', 'PCB Layout' and 'Copper Bottom Image' are included included subsequent pages.

Eagle CAD Design Rules

EAGLE CAD DESIGN RULES export

description[en] = <b>Wide Tolatances</b>\n<p>\nDesign rules to facilitate\nmanufacture of board with \n high accuracy & repeatability</p>

layerSetup = (1*16)mtCopper = 0.035mm 0.035mm 0.035mm 0.035mm 0.035mm 0.035mm 0.035mm 0.035mm 0.035mm 0.035mm 0.035mm 0.035mm 0.035mm 0.035mm 0.035mm 0.035mmmtIsolate = 1.5mm 0.15mm 0.2mm 0.15mm 0.2mm 0.15mm 0.2mm 0.15mm 0.2mm 0.15mm 0.2mm 0.15mm 0.2mm 0.15mm 0.2mmmdWireWire = 18milmdWirePad = 18milmdWireVia = 8milmdPadPad = 12milmdPadVia = 8milmdViaVia = 8milmdSmdPad = 8milmdSmdVia = 8milmdSmdSmd = 8milmdViaViaSameLayer = 8milmnLayersViaInSmd = 2mdCopperDimension = 10milmdDrill = 8milmdSmdStop = 0milmsWidth = 16milmsDrill = 20milmsMicroVia = 9.99mmmsBlindViaRatio = 0.500000rvPadTop = 0.250000rvPadInner = 0.250000rvPadBottom = 0.300000rvViaOuter = 0.250000rvViaInner = 0.250000rvMicroViaOuter = 0.250000rvMicroViaInner = 0.250000rlMinPadTop = 12milrlMaxPadTop = 20milrlMinPadInner = 10milrlMaxPadInner = 20milrlMinPadBottom = 20milrlMaxPadBottom = 30milrlMinViaOuter = 10milrlMaxViaOuter = 20mil

rlMinViaInner = 10milrlMaxViaInner = 20milrlMinMicroViaOuter = 4milrlMaxMicroViaOuter = 20milrlMinMicroViaInner = 4milrlMaxMicroViaInner = 20milpsTop = -1psBottom = -1psFirst = -1psElongationLong = 100psElongationOffset = 100mvStopFrame = 1.000000mvCreamFrame = 0.000000mlMinStopFrame = 4milmlMaxStopFrame = 4milmlMinCreamFrame = 0milmlMaxCreamFrame = 0milmlViaStopLimit = 25milsrRoundness = 0.000000srMinRoundness = 0milsrMaxRoundness = 0milslThermalGap = 0.500000slMinThermalGap = 20milslMaxThermalGap = 100milslAnnulusIsolate = 20milslThermalIsolate = 10milslAnnulusRestring = 0slThermalRestring = 1slThermalsForVias = 0checkGrid = 0checkAngle = 0checkFont = 1checkRestrict = 1useDiameter = 13maxErrors = 50

Copper Bottom Layer

Replace Page

PCB Assembly Diagram

Replace Page

SPICE SimulationSPICE simulation of the circuit was performed using the software “LTSpice IV” from Linear Corporation. Operational amplifier TL071 model was obtained from National Semiconductor's library.

Transient analysis and AC frequency analysis was carried out in the software.

Transient analysis was run for a simulated time of 10ms and showed sufficient analog mixing of signals.

AC response was near about flat between 100 Hz and 18 KHz indicating good audio frequency response. The resultant graphs of the analysis, SPICE netlist files and simulation files are attached on subsequent pages.

Analysis Screen-shots

Illustration 10: AC analysis of circuit.

Illustration 9: Transient analysis: 10ms

SPICE Net-list

Transient Analysis

* E:\Projects and Papers\SE project\Audio Mixer\CAD Files\Spice\Audio Mixer -2.ascXU1 0 N001 V+ V- N002 TL071R1 N001 P001 1K tol=1 pwr=0.1R12 N002 N001 100kV3 N005 0 SINE(0 0.010 1.5k) AC 0.01V1 V+ 0 9V2 0 V- 9XU2 0 N003 V+ V- N004 TL071C2 N006 N002 10µR2 N003 N006 47KR3 N004 N003 100kC1 P001 N005 10µXU3 0 N007 V+ V- N008 TL071XU4 0 N011 V+ V- N012 TL071R4 N007 N009 1KR5 N011 N014 1KR6 N003 N010 47KR7 N003 N013 47KC3 N010 N008 10µC4 N013 N012 10µV4 N009 0 SINE(0 0.010 1K) AC 0.01V5 N014 0 SINE(0 0.010 2K) AC 0.01R8 N008 N007 100kR9 N012 N011 100k.include TL071.MOD.tran 10m.backanno.end

AC Frequency Analysis

* E:\Projects and Papers\SE project\Audio Mixer\CAD Files\Spice\Audio Mixer -2.ascXU1 0 N001 V+ V- N002 TL071R1 N001 P001 1K tol=1 pwr=0.1R12 N002 N001 100kV3 N005 0 SINE(0 0.010 1.5k) AC 0.01V1 V+ 0 9V2 0 V- 9XU2 0 N003 V+ V- N004 TL071C2 N006 N002 10µR2 N003 N006 47KR3 N004 N003 100kC1 P001 N005 10µXU3 0 N007 V+ V- N008 TL071XU4 0 N011 V+ V- N012 TL071R4 N007 N009 1KR5 N011 N014 1KR6 N003 N010 47KR7 N003 N013 47KC3 N010 N008 10µC4 N013 N012 10µV4 N009 0 SINE(0 0.010 1K) AC 0.01V5 N014 0 SINE(0 0.010 2K) AC 0.01R8 N008 N007 100kR9 N012 N011 100k.include TL071.MOD.ac oct 10 20 20000.backanno.end

SPICE Plot Export – AC analysisFreq. V(n004)

2.00000e+001

(1.50426e+001dB,1.15028e+001°)

2.14355e+001

(1.51411e+001dB,1.11283e+001°)

2.29740e+001

(1.52338e+001dB,1.07297e+001°)

2.46229e+001

(1.53202e+001dB,1.03122e+001°)

2.63902e+001

(1.54003e+001dB,9.88121e+000°)

2.82843e+001

(1.54740e+001dB,9.44148e+000°)

3.03143e+001

(1.55416e+001dB,8.99763e+000°)

3.24901e+001

(1.56031e+001dB,8.55378e+000°)

3.48220e+001

(1.56588e+001dB,8.11357e+000°)

3.73213e+001

(1.57091e+001dB,7.68008e+000°)

4.00000e+001

(1.57543e+001dB,7.25591e+000°)

4.28709e+001

(1.57948e+001dB,6.84315e+000°)

4.59479e+001

(1.58309e+001dB,6.44343e+000°)

4.92458e+001

(1.58630e+001dB,6.05797e+000°)

5.27803e+001

(1.58915e+001dB,5.68763e+000°)

5.65685e+001

(1.59168e+001dB,5.33292e+000°)

6.06287e+001

(1.59391e+001dB,4.99410e+000°)

6.49802e+001

(1.59588e+001dB,4.67121e+000°)

6.96440e+001

(1.59761e+001dB,4.36408e+000°)

7.46426e+001

(1.59913e+001dB,4.07240e+000°)

8.00000e+001

(1.60047e+001dB,3.79574e+000°)

8.57419e+001

(1.60164e+001dB,3.53358e+000°)

9.18959e+001

(1.60267e+001dB,3.28533e+000°)

9.84916e+001

(1.60357e+001dB,3.05035e+000°)

1.05561e+002

(1.60436e+001dB,2.82796e+000°)

1.13137e+002

(1.60505e+001dB,2.61748e+000°)

1.21257e+002

(1.60565e+001dB,2.41819e+000°)

1.29960e+002

(1.60618e+001dB,2.22940e+000°)

1.39288e+002

(1.60664e+001dB,2.05040e+000°)

1.49285e+002

(1.60704e+001dB,1.88051e+000°)

1.60000e+002

(1.60739e+001dB,1.71904e+000°)

1.71484e+002

(1.60769e+001dB,1.56533e+000°)

1.83792e+002

(1.60795e+001dB,1.41875e+000°)

1.96983e+002

(1.60818e+001dB,1.27864e+000°)

2.11121e+002

(1.60838e+001dB,1.14442e+000°)

2.26274e+002

(1.60856e+001dB,1.01548e+000°)

2.42515e+002

(1.60871e+001dB,8.91235e-001°)

2.59921e+002

(1.60884e+001dB,7.71133e-001°)

2.78576e+002

(1.60895e+001dB,6.54619e-001°)

2.98571e+002

(1.60905e+001dB,5.41156e-001°)

3.20000e+002

(1.60913e+001dB,4.30217e-001°)

3.42968e+002

(1.60920e+001dB,3.21282e-001°)

3.67583e+002

(1.60927e+001dB,2.13841e-001°)

3.93966e+002

(1.60932e+001dB,1.07387e-001°)

4.22243e+002

(1.60936e+001dB,1.41578e-003°)

4.52548e+002 (1.60939e+001dB,-1.04575e-001°)

4.85029e+002 (1.60942e+001dB,-

2.11089e-001°)

5.19842e+002 (1.60944e+001dB,-3.18634e-001°)

5.57152e+002 (1.60945e+001dB,-4.27722e-001°)

5.97141e+002 (1.60946e+001dB,-5.38876e-001°)

6.40000e+002 (1.60947e+001dB,-6.52625e-001°)

6.85935e+002 (1.60946e+001dB,-7.69514e-001°)

7.35167e+002 (1.60945e+001dB,-8.90102e-001°)

7.87932e+002 (1.60944e+001dB,-1.01497e+000°)

8.44485e+002 (1.60942e+001dB,-1.14470e+000°)

9.05097e+002 (1.60939e+001dB,-1.27994e+000°)

9.70059e+002 (1.60935e+001dB,-1.42131e+000°)

1.03968e+003 (1.60931e+001dB,-1.56950e+000°)

1.11430e+003 (1.60925e+001dB,-1.72522e+000°)

1.19428e+003 (1.60919e+001dB,-1.88920e+000°)

1.28000e+003 (1.60912e+001dB,-2.06223e+000°)

1.37187e+003 (1.60903e+001dB,-2.24514e+000°)

1.47033e+003 (1.60893e+001dB,-2.43879e+000°)

1.57586e+003 (1.60882e+001dB,-2.64411e+000°)

1.68897e+003 (1.60868e+001dB,-2.86206e+000°)

1.81019e+003 (1.60852e+001dB,-3.09368e+000°)

1.94012e+003 (1.60835e+001dB,-3.34006e+000°)

2.07937e+003 (1.60814e+001dB,-3.60237e+000°)

2.22861e+003 (1.60790e+001dB,-3.88182e+000°)

2.38856e+003 (1.60763e+001dB,-4.17972e+000°)

2.56000e+003 (1.60731e+001dB,-4.49747e+000°)

2.74374e+003 (1.60695e+001dB,-4.83652e+000°)

2.94067e+003 (1.60654e+001dB,-5.19845e+000°)

3.15173e+003 (1.60606e+001dB,-5.58489e+000°)

3.37794e+003 (1.60551e+001dB,-5.99761e+000°)

3.62039e+003 (1.60489e+001dB,-6.43845e+000°)

3.88023e+003 (1.60417e+001dB,-6.90938e+000°)

4.15873e+003 (1.60334e+001dB,-7.41247e+000°)

4.45722e+003 (1.60239e+001dB,-7.94988e+000°)

4.77713e+003 (1.60131e+001dB,-8.52392e+000°)

5.12000e+003 (1.60007e+001dB,-9.13697e+000°)

5.48748e+003 (1.59864e+001dB,-9.79156e+000°)

5.88134e+003 (1.59701e+001dB,-1.04903e+001°)

6.30346e+003 (1.59515e+001dB,-

1.12359e+001°)

6.75588e+003 (1.59302e+001dB,-1.20311e+001°)

7.24077e+003 (1.59058e+001dB,-1.28788e+001°)

7.76047e+003 (1.58780e+001dB,-1.37819e+001°)

8.31746e+003 (1.58462e+001dB,-1.47434e+001°)

8.91444e+003 (1.58100e+001dB,-1.57661e+001°)

9.55426e+003 (1.57688e+001dB,-1.68530e+001°)

1.02400e+004 (1.57220e+001dB,-1.80068e+001°)

1.09750e+004 (1.56687e+001dB,-1.92301e+001°)

1.17627e+004 (1.56084e+001dB,-2.05254e+001°)

1.26069e+004 (1.55401e+001dB,-2.18947e+001°)

1.35118e+004 (1.54629e+001dB,-2.33397e+001°)

1.44815e+004 (1.53759e+001dB,-2.48619e+001°)

1.55209e+004 (1.52780e+001dB,-2.64617e+001°)

1.66349e+004 (1.51683e+001dB,-2.81394e+001°)

1.78289e+004 (1.50454e+001dB,-2.98942e+001°)

1.91085e+004 (1.49085e+001dB,-3.17246e+001°)

2.00000e+004 (1.48101e+001dB,-3.29689e+001°)

Operational Amplifier – TL071 SPICE model

* TL071 OPERATIONAL AMPLIFIER "MACROMODEL" SUBCIRCUIT* CREATED USING PARTS RELEASE 4.01 ON 06/16/89 AT 13:08* (REV N/A) SUPPLY VOLTAGE: +/-15V* CONNECTIONS: NON-INVERTING INPUT* | INVERTING INPUT* | | POSITIVE POWER SUPPLY* | | | NEGATIVE POWER SUPPLY* | | | | OUTPUT* | | | | |.SUBCKT TL071 1 2 3 4 5* C1 11 12 3.498E-12 C2 6 7 15.00E-12 DC 5 53 DX DE 54 5 DX DLP 90 91 DX DLN 92 90 DX DP 4 3 DX EGND 99 0 POLY(2) (3,0) (4,0) 0 .5 .5 FB 7 99 POLY(5) VB VC VE VLP VLN 0 4.715E6 -5E6 5E6 5E6 -5E6 GA 6 0 11 12 282.8E-6 GCM 0 6 10 99 8.942E-9 ISS 3 10 DC 195.0E-6 HLIM 90 0 VLIM 1K J1 11 2 10 JX J2 12 1 10 JX R2 6 9 100.0E3 RD1 4 11 3.536E3 RD2 4 12 3.536E3 RO1 8 5 150 RO2 7 99 150 RP 3 4 2.143E3 RSS 10 99 1.026E6 VB 9 0 DC 0 VC 3 53 DC 2.200 VE 54 4 DC 2.200 VLIM 7 8 DC 0 VLP 91 0 DC 25 VLN 0 92 DC 25.MODEL DX D(IS=800.0E-18).MODEL JX PJF(IS=15.00E-12 BETA=270.1E-6 VTO=-1).ENDS

.

SPICE Analysis Graphs

AC Frequency analysis

Transient Analysis Graphs

TroubleshootingThe circuit functioned as designed for the most part, except on two counts: both mechanical.

The 3.5 mm TRS connector had flat pins which did not fit correctly in the 1.1 mm drill hole. We had to carefully extend the holes laterally to allow the pins to slide through. This was done using a 0.3mm drill bit. The fine drill bit was mounted onto the drill chuck and lowered into the hole and the PCB was moved from side to side. This extended the size of the hole by a hair width and the jack slid inside.

The second bug arose in the fit of the TRS connector. As the connector was not mounted at the extreme edge of the board, the fitting with the audio jacks were not ideal. This was solved by grinding the edge of the board to reduce its dimensions. 400 grit sandpaper and a laminate blade was used for the purpose.

We also provided two external Male 3.5 mm TRS connectors as we noted that most devices seemed to have Female ports.

Illustration 11: TRS connector mechanical fitting was a problem

Bill of Materials

Part-list exported from C:/Documents and Settings/Shaunak/My Documents/eagle/Audio Mixer V2/Audio Mixer V2.sch at 28/4/2010 12:16:21 PM

Part Value Device Package Description C1 10u CAP_POLPTH2 CPOL-RADIAL-10UF-25V Capacitor Polarized C2 10u CAP_POLPTH2 CPOL-RADIAL-10UF-25V Capacitor Polarized C3 10u CAP_POLPTH2 CPOL-RADIAL-10UF-25V Capacitor Polarized C4 1u CAP_POLPTH2 CPOL-RADIAL-10UF-25V Capacitor Polarized C5 1u CAP_POLPTH2 CPOL-RADIAL-10UF-25V Capacitor Polarized C6 1u CAP_POLPTH2 CPOL-RADIAL-10UF-25V Capacitor Polarized C7 10u CAP_POLPTH2 CPOL-RADIAL-10UF-25V Capacitor Polarized G1 AB9V AB9V AB9V 9-V BATTERY CLIP G2 AB9V AB9V AB9V 9-V BATTERY CLIP IC1 TL071P TL071P DIL08 OP AMP IC2 TL071P TL071P DIL08 OP AMP IC3 TL071P TL071P DIL08 OP AMP IC4 TL071P TL071P DIL08 OP AMP R1 10K TRIM_EU-CIP20C-4MM CIP20C-4MM POTENTIOMETER R2 10K TRIM_EU-CIP20C-4MM CIP20C-4MM POTENTIOMETER R3 10K TRIM_EU-CIP20C-4MM CIP20C-4MM POTENTIOMETER R4 100K R-US_0207/10 0207/10 RESISTOR, American symbolR5 100K R-US_0207/10 0207/10 RESISTOR, American symbolR6 100K R-US_0207/10 0207/10 RESISTOR, American symbolR7 47K R-US_0207/10 0207/10 RESISTOR, American symbolR8 47K R-US_0207/10 0207/10 RESISTOR, American symbolR9 47K R-US_0207/10 0207/10 RESISTOR, American symbolR10 100K R-US_0207/10 0207/10 RESISTOR, American symbolR11 10K R-US_0207/10 0207/10 RESISTOR, American symbolR12 1K R-US_0207/10 0207/10 RESISTOR, American symbolR13 1K R-US_0207/10 0207/10 RESISTOR, American symbolR14 1K R-US_0207/10 0207/10 RESISTOR, American symbolX1 PG203J PG203J PG203J MIC/HEADPHONE JACK X2 PG203J PG203J PG203J MIC/HEADPHONE JACK X3 PG203J PG203J PG203J MIC/HEADPHONE JACK X4 PG203J PG203J PG203J MIC/HEADPHONE JACK

ConclusionWe have successfully simulated, prototyped and designed a analog audio mixer with the help of Computer Aided Tools.

The final construction was carried out on a 3 by 4 inch Phenolic Laminate board with a copper layer on one side. The board was drilled, cut and checked. Components were then tested and assembled/soldered on it.

Mechanical fixture and support was provided with a Cyanoacrylate compount which serves as both an adhesive as well as an insulator.

Through the project we have enlisted the following CAD tools:• EAGLE Cad: Schematic entry and board layout design• LTSpice: Circuit simulation• OpenOffice Writer: Latex entry and report compilation• GIMP: Image and graph editing.

The output of the project can easily be demonstrated on a speaker or a pair of headphones.

The practical a commercial considerations of the project are clear. It can be used for mixing two audio sources, be it from microphones, mobile-phones, portable media players or computers.

The project can be used as a viable alternative to basic commercial solutions.

Project Pictures

Illustration 13: After Assembly

Illustration 12: Before Assembly

Bibliography

Books, Journals and Periodicals

• Circuit Cellar – September 2009

• Silicon Chip Magazine – August 2009

• OP-Amps and Linear Integrated Circuits – Gayakwad

• Electronic Devices and Circuit Theory – Boylestad – Nashelsky

• Basic Electricity and Semiconductor Devices – Patil – Chitnis

• Applied and Digital Electronics - Patil – Chitnis

• The essence of Printed Circuit Boards Design with EAGLE - Tetsuya Gokan

• SPICE Simulation Fundamentals – National Instruments

• Fundamentals of Physics – Resnick – Halliday - Walker

Websites

• SPICE (Simulation Program with Integrated Circuit Emphasis): http://en.wikipedia.org/wiki/SPICE

• Cyanoacrylate: http://en.wikipedia.org/wiki/Cyanoacrylate

• Operational amplifier: http://en.wikipedia.org/wiki/Op_amps

• SPICE overview: http://bwrc.eecs.berkeley.edu/classes/icbook/spice/UserGuide/overview_fr.html

• Phenolic Laminates: http://k-mac-plastics.net/phenolics.htm

• Toner Transfer method: http://www.dr-lex.be/hardware/tonertransfer.html

• Edaboards: http://www.edaboard.com/viewtopic.php?t=35875&highlight=eagle

Multimedia

• PCB using toner transfer: http://www.youtube.com/watch?v=QQupRXEqOz4

• Etch a PCB: http://www.youtube.com/watch?v=kQk6b3MvzkU

Illustration IndexIllustration 1: Professional Mixer..............................................................................................................2Illustration 2: Controls and LFO envelope [DM2000]..............................................................................3Illustration 3: Mixing Curves Display [DM2000].....................................................................................3Illustration 4: Pin Configuration of Tl071.................................................................................................7Illustration 5: Typical response of TL072..................................................................................................8Illustration 6: Block Diagram of Operational Amplifier............................................................................9Illustration 7: Summing Amplifier...........................................................................................................10Illustration 8: Fundamental of Operation.................................................................................................11Illustration 9: Transient analysis: 10ms...................................................................................................17Illustration 10: AC analysis of circuit......................................................................................................17Illustration 11: TRS connector mechanical fitting was a problem...........................................................25Illustration 12: Before Assembly.............................................................................................................28Illustration 13: After Assembly................................................................................................................28