The above link is supposed to take you to section 5.4. If it takes you to the top of chapter 5 instead you will have to scroll down to section 5.4 which contains the operating instructions.
Introduction.Intermodulation Distortion (IMD) seems to be the step child of high fi amplifier specifications. I think I know the reason, advertising. Based on what is admittedly a small sample, the IMD figures for a given amplifier are anywhere from 3 to 10 times the THD (total harmonic distortion) figures. So if you were a manufacturer of amplifiers would you post figures that looked much worse than your competitors? I think not. But things don't have to be like that in the hobby world.
I will show in section 1.4 of this work why IMD figures are larger than THD values. Also I will show why IMD is much more objectionable to the ear than harmonic distortion. I think that we as hobbyist should have equipment to measure IMD as well as THD.
Construction of a harmonic distortion analyzer is rather difficult involving some rather high impedance low noise circuits which require good shielding. The level of measurement, typically down to 0.1 % full scale and a frequency range from 5 Hz to 600 kHz in top of the line instruments requires low noise active devices and large value resistors that may not be available off the internet. Automatic null adjustment is a must because manual adjustment is too sensitive to be done day in and day out while keeping one's sanity.
An IM analyzer only needs to be adjusted for 100% and so is much easier to use. In construction some care must be taken to make sure that the signal source does not contain intermodulation products and that the test signal does not leak into the measurement circuits. In the project shown here shielding is accomplished through the use of die cast aluminum boxes to shield the various parts of the instrument from one another. Construction uses prototyping boards so no board etching is needed. No exotic parts are used making the project doable by anyone who has access to the internet.
Chapter 1 Perception and Theory of Distortion.
1.1 The Theory of Measuring THD (Total Harmonic Distortion).
1.1.1 The Input Attenuator and Input Buffer1.2 The Theory of Measuring IMD (InterModulation Distortion).
1.1.2 The Notch Filter.
1.1.3 The Voltmeter.
1.1.4 The Output.
1.1.5 Making the Measurement.
1.1.6 How all this Works Together.
1.1.7 An Alternate Method.
1.2.1 Test Signal Generator.1.3 How We Perceive Distortion.
188.8.131.52 Low Frequency generator.1.2.2 Input Attenuator.
184.108.40.206 High Frequency Generator.
220.127.116.11 Linear Mixer.
18.104.22.168 Output Buffer.
1.2.3 Input Buffer.
1.2.4 High Pass filter.
1.2.5 Detector (Rectifier.
1.2.6 Low Pass Filter.
1.2.7 The Meter.
1.2.8 Instrument Calibration by the DC method.
1.2.9 Calibration by the Two Signal Method.
1.3.1 Harmonic Distortion.1.4 The mathematics of distortion.
1.3.2 Intermodulation Distortion.
1.4.1 Harmonic Distortion and the Gain Polynomial./1.5 Conclusion.
22.214.171.124 The Gain Polynomial.1.4.2 Intermodulation Distortion.
126.96.36.199 The Input Signal.
188.8.131.52 Amplitudes of the Harmonics.
184.108.40.206 The Gain Polynomial.
220.127.116.11 The Input Signal.
18.104.22.168 The Binomial Theorem.
Chapter 2 Theory of Operation.
2.1 Design Considerations.
2.2 Overall Diagram
2.3 Circuit Description.
2.3.1 Control Panel.2.3 Operating Characteristics.
2.3.2 Low Frequency Generator.
2.3.3 High frequency Generator.
2.3.4 Linear Mixer and Output Buffer.
2.3.5 Input Buffer and High Pass Filter.
2.3.6 Linear Rectifier and Low Pass Filter.
2.3.7 Power Supply.
Chapter 3 Parts Acquisition.
3.1 Flat Washers.
3.2 Ordering Parts From DigiKey.
3.2.1 5% Capacitors.3.3 Insulating Washers.
3.2.2 10% Capacitors.
3.4 The Power Transformer.
3.5 Parts List.
3.6 Something I couldn't find.
3.7 Other Parts and Supplies.
Chapter 4 Construction.
4.1 Die Cast Aluminum Box Preparation.Chapter 5 Initial Testing, Calibration, and Operation.
4.2 Circuit Board Preparation.
4.3 Module Construction.
4.3.1 Low Frequency Generator (LF Gen) Board.4.4 Testing, Adjusting, and Troubleshooting, the Modules.
22.214.171.124 IC socket.4.3.2 High Frequency Generator (HF Gen) Board
126.96.36.199 Copper Ground Wire.
188.8.131.52 Grounding Columns.
184.108.40.206 Horizontal Resistors.
220.127.116.11 Vertical Resistors.
18.104.22.168 Semiconductor Devices.
22.214.171.124 External Connecting Wires.
126.96.36.199 Regulator IC Protection Diodes.
188.8.131.52 Drilling Wire Escape Holes in the Box.
184.108.40.206 IC Sockets.4.3.3 Input Buffer and High Pass Filter Board.
220.127.116.11 Copper Grounding Wire.
18.104.22.168 Grounding Columns.
22.214.171.124 Jumpers, Filter Section.
126.96.36.199 Horizontal Resistors, Filter Section.
188.8.131.52 Vertical Resistors, Filter Section.
184.108.40.206 Capacitors, Filter Section.
220.127.116.11 Semiconductor Devices, Filter Section.
18.104.22.168 Jumpers, Oscillator Section.
22.214.171.124 Horizontal Resistors, Oscillator Section. 126.96.36.199 Vertical Resistors, Oscillator Section.
188.8.131.52 Capacitors, Oscillator Section.
184.108.40.206 Semiconductor Devices and Trim Pots, Oscillator Section.
220.127.116.11 Capacitors on Foil Side of Board.
18.104.22.168 External Connecting Wires.
22.214.171.124 Drilling the Adjustment Screw Access Holes.
126.96.36.199 IC Sockets. 188.8.131.52 Grounding Wire.4.3.4 Linear Rectifier and Low Pass Filter.
184.108.40.206 Column Grounding Wires.
220.127.116.11 Jumper Wires.
18.104.22.168 Capacitors on Component Side of Board.
22.214.171.124 Capacitors on Foil Side of Board.
126.96.36.199 Semiconductor Devices.
188.8.131.52 Trimming Potentiometer.
184.108.40.206 External Connecting Wires.
220.127.116.11 IC Sockets.4.3.5 Linear Mixer and Output Buffer.
18.104.22.168 Grounding Wire and Column Grounds.
22.214.171.124 Jumper Wires.
126.96.36.199 A Pair of Diodes.
188.8.131.52 Capacitors on Component Side of Board.
184.108.40.206 Capacitors on Foil Side of Board.
220.127.116.11 Remaining capacitors on component side of board.
18.104.22.168 Semiconductor Devices and Potentiometer.
22.214.171.124 External Connecting Wires.
126.96.36.199 The Leftover Box.
188.8.131.52 Board Preparation.
184.108.40.206 IC Sockets.
220.127.116.11 Grounding Wires and Capacitors on Foil Side of Board.
18.104.22.168 Semiconductor Devices.
22.214.171.124 External Connecting Wires.
4.4.1 Low Frequency Generator.4.5 Chassis Assembly.
126.96.36.199 Setting Up the Test.4.4.2 High Frequency Generator.
188.8.131.52 Voltage and Current Measurements.
184.108.40.206 Filter Frequency Response.
220.127.116.11 Setting Up the Test.4.4.3 Input Buffer and High Pass Filter.
18.104.22.168 Voltage and Current Measurements.
22.214.171.124 Filter Frequency Response.
126.96.36.199 Setting Up the Test.4.4.4 Linear Rectifier and Low Pass Filter.
188.8.131.52 Voltage and Current Measurements.
184.108.40.206 Filter Frequency Response.
220.127.116.11 Setting Up the Test.4.4.5 Linear Mixer and Output Buffer.
18.104.22.168 Voltage and Current Measurements.
22.214.171.124 Filter Frequency Response.
126.96.36.199 Setting Up the Test.
188.8.131.52 Voltage and Current Measurements.
4.5.1 Preparing the Panel/Chassis.4.6 Electrically Bonding the Two Panels.
184.108.40.206 Drilling the Panel.4.5.2 Preparing the Switches..
220.127.116.11 Front Panel Label.
4.5.3 Parts Mounting.
18.104.22.168 Mounting the Switches.4.5.4 Chassis Wiring Part 1.
22.214.171.124 Mounting the Potentiometers.
126.96.36.199 Mounting the BNC Connectors.
188.8.131.52 Power Supply Rectifier and Filter.4.5.5 Chassis Wiring Part 2, Module Installation.
4.5.6 Power Transformer and 120 Volt Primary Wiring.
184.108.40.206a If Both Leads Are Solid Black.4.5.7 Photograph of Finished Product.
220.127.116.11b If One Lead is Solid Black and the Other One is Black With a Colored Stripe.
18.104.22.168 Line Cord Installation.
4.7 The Smoke Test.
5.1 Selecting a Readout Device.Chapter 6 Calibration.
5.2 Initial Tests.
5.2.1 Testing the Signal Source.5.3 Final Assembly.
5.2.2 Testing the Measuring Circuit.
5.2.3 Checking the Input Attenuator.
5.4 Operating Instructions.
5.5 First Measurement.
5.5.1 Discovery of a Design Mistake.
6.1 Calibration to 0.316 volt = 100%.
6.1.1 Adjusting Trimmer in M 4.6.2 Calibration to 1.00 volt = 100%.
6.1.2a Method 1,Two HF Generators.
6.1.2b Method 2, Fancy Schmancy Function Generator.
6.1.2c Method 3, Post Detection DC Level.
6.2.1 Adjusting Trimmer in M 4.
6.2.2a Method 1,Two HF Generators.
6.2.2b Method 2, Fancy Schmancy Function Generator.
6.6.2c Method 3, Post Detection DC Level.
Chapter 7 In Case of Trouble.
7.1 Review of Operating Instructions.Chapter 8 A Distortion Reference.
7.2 Shooting Trouble.
7.2.2 The Power Supply.
7.2.3 The Signal Source.
7.2.4 The Measuring Circuit.
7.2.5 The Input Attenuator.
8.1 The Design Approach.
8.1.1 Circuit Description and Theory Of Operation.8.2 Construction.
8.2.1 Drilling holes in the box.8.3 Initial Test>
8.2.2 Parts Mounting.
8.2.3 Switch Prewiring.
8.2.4 Switch Label.
8.2.5 Final Assembly.
8.4 Measured Values of IMD and THD.
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