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.
220.127.116.11 Low Frequency generator.1.2.2 Input Attenuator.
18.104.22.168 High Frequency Generator.
22.214.171.124 Linear Mixer.
126.96.36.199 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.
188.8.131.52 The Gain Polynomial.1.4.2 Intermodulation Distortion.
184.108.40.206 The Input Signal.
220.127.116.11 Amplitudes of the Harmonics.
18.104.22.168 The Gain Polynomial.
22.214.171.124 The Input Signal.
126.96.36.199 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.
188.8.131.52 IC socket.4.3.2 High Frequency Generator (HF Gen) Board
184.108.40.206 Copper Ground Wire.
220.127.116.11 Grounding Columns.
18.104.22.168 Horizontal Resistors.
22.214.171.124 Vertical Resistors.
126.96.36.199 Semiconductor Devices.
188.8.131.52 External Connecting Wires.
184.108.40.206 Regulator IC Protection Diodes.
220.127.116.11 Drilling Wire Escape Holes in the Box.
18.104.22.168 IC Sockets.4.3.3 Input Buffer and High Pass Filter Board.
22.214.171.124 Copper Grounding Wire.
126.96.36.199 Grounding Columns.
188.8.131.52 Jumpers, Filter Section.
184.108.40.206 Horizontal Resistors, Filter Section.
220.127.116.11 Vertical Resistors, Filter Section.
18.104.22.168 Capacitors, Filter Section.
22.214.171.124 Semiconductor Devices, Filter Section.
126.96.36.199 Jumpers, Oscillator Section.
188.8.131.52 Horizontal Resistors, Oscillator Section. 184.108.40.206 Vertical Resistors, Oscillator Section.
220.127.116.11 Capacitors, Oscillator Section.
18.104.22.168 Semiconductor Devices and Trim Pots, Oscillator Section.
22.214.171.124 Capacitors on Foil Side of Board.
126.96.36.199 External Connecting Wires.
188.8.131.52 Drilling the Adjustment Screw Access Holes.
184.108.40.206 IC Sockets. 220.127.116.11 Grounding Wire.4.3.4 Linear Rectifier and Low Pass Filter.
18.104.22.168 Column Grounding Wires.
22.214.171.124 Jumper Wires.
126.96.36.199 Capacitors on Component Side of Board.
188.8.131.52 Capacitors on Foil Side of Board.
184.108.40.206 Semiconductor Devices.
220.127.116.11 Trimming Potentiometer.
18.104.22.168 External Connecting Wires.
22.214.171.124 IC Sockets.4.3.5 Linear Mixer and Output Buffer.
126.96.36.199 Grounding Wire and Column Grounds.
188.8.131.52 Jumper Wires.
184.108.40.206 A Pair of Diodes.
220.127.116.11 Capacitors on Component Side of Board.
18.104.22.168 Capacitors on Foil Side of Board.
22.214.171.124 Remaining capacitors on component side of board.
126.96.36.199 Semiconductor Devices and Potentiometer.
188.8.131.52 External Connecting Wires.
184.108.40.206 The Leftover Box.
220.127.116.11 Board Preparation.
18.104.22.168 IC Sockets.
22.214.171.124 Grounding Wires and Capacitors on Foil Side of Board.
126.96.36.199 Semiconductor Devices.
188.8.131.52 External Connecting Wires.
4.4.1 Low Frequency Generator.4.5 Chassis Assembly.
184.108.40.206 Setting Up the Test.4.4.2 High Frequency Generator.
220.127.116.11 Voltage and Current Measurements.
18.104.22.168 Filter Frequency Response.
22.214.171.124 Setting Up the Test.4.4.3 Input Buffer and High Pass Filter.
126.96.36.199 Voltage and Current Measurements.
188.8.131.52 Filter Frequency Response.
184.108.40.206 Setting Up the Test.4.4.4 Linear Rectifier and Low Pass Filter.
220.127.116.11 Voltage and Current Measurements.
18.104.22.168 Filter Frequency Response.
22.214.171.124 Setting Up the Test.4.4.5 Linear Mixer and Output Buffer.
126.96.36.199 Voltage and Current Measurements.
188.8.131.52 Filter Frequency Response.
184.108.40.206 Setting Up the Test.
220.127.116.11 Voltage and Current Measurements.
4.5.1 Preparing the Panel/Chassis.4.6 Electrically Bonding the Two Panels.
18.104.22.168 Drilling the Panel.4.5.2 Preparing the Switches..
22.214.171.124 Front Panel Label.
4.5.3 Parts Mounting.
126.96.36.199 Mounting the Switches.4.5.4 Chassis Wiring Part 1.
188.8.131.52 Mounting the Potentiometers.
184.108.40.206 Mounting the BNC Connectors.
220.127.116.11 Power Supply Rectifier and Filter.4.5.5 Chassis Wiring Part 2, Module Installation.
4.5.6 Power Transformer and 120 Volt Primary Wiring.
18.104.22.168a If Both Leads Are Solid Black.4.5.7 Photograph of Finished Product.
22.214.171.124b If One Lead is Solid Black and the Other One is Black With a Colored Stripe.
126.96.36.199 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.
Back to Fun With Tubes.
Back to Fun With Transistors.
Back to Table of Contents.
Back to Top.