# Build an I M Distortion Analyzer.

#### OPERATING INSTRUCTIONS. Section 5.4

> > 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 Buffer
> > 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   The Theory of Measuring IMD (InterModulation Distortion).
> > 1.2.1   Test Signal Generator.
> > 1.2.1.1   Low Frequency generator.
> > 1.2.1.2   High Frequency Generator.
> > 1.2.1.3   Linear Mixer.
> > 1.2.1.4   Output Buffer.
> > 1.2.2   Input Attenuator.
> > 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   How We Perceive Distortion.
> > 1.3.1   Harmonic Distortion.
> > 1.3.2   Intermodulation Distortion.
> > 1.4   The mathematics of distortion.
> > 1.4.1   Harmonic Distortion and the Gain Polynomial./
> > 1.4.1.1   The Gain Polynomial.
> > 1.4.1.2   The Input Signal.
> > 1.4.1.3   Amplitudes of the Harmonics.
> > 1.4.1.4   Example.
> > 1.4.2   Intermodulation Distortion.
> > 1.4.2.1   The Gain Polynomial.
> > 1.4.2.2   The Input Signal.
> > 1.4.2.3   The Binomial Theorem.
> > 1.5   Conclusion.

> > Chapter 2   Theory of Operation.
> > 2.1   Design Considerations.
> > 2.2   Overall Diagram
> > 2.3   Circuit Description.
> > 2.3.1   Control Panel.
> > 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.
> > 2.3   Operating Characteristics.

> > Chapter 3   Parts Acquisition.
> > 3.1 Flat Washers.
> > 3.2 Ordering Parts From DigiKey.
> > 3.2.1 5% Capacitors.
> > 3.2.2 10% Capacitors.
> > 3.2.3 Resistors.
> > 3.3 Insulating Washers.
> > 3.4 The Power Transformer.
> > 3.5 Parts List.
> > 3.6 Something I couldn't find.
> > 3.7 Other Parts and Supplies.
> > 3.8 Tools.

> > Chapter 4   Construction.
> > 4.1   Die Cast Aluminum Box Preparation.
> > 4.2   Circuit Board Preparation.
> > 4.3   Module Construction.
> > 4.3.1   Low Frequency Generator (LF Gen) Board.
> > 4.3.1.1   IC socket.
> > 4.3.1.2   Copper Ground Wire.
> > 4.3.1.3   Grounding Columns.
> > 4.3.1.4   Jumpers.
> > 4.3.1.5   Horizontal Resistors.
> > 4.3.1.6   Vertical Resistors.
> > 4.3.1.7   Capacitors.
> > 4.3.1.8   Semiconductor Devices.
> > 4.3.1.9   External Connecting Wires.
> > 4.3.1.10   Regulator IC Protection Diodes.
> > 4.3.1.11   Drilling Wire Escape Holes in the Box.
> > 4.3.2   High Frequency Generator (HF Gen) Board
> > 4.3.2.1   IC Sockets.
> > 4.3.2.2   Copper Grounding Wire.
> > 4.3.2.3   Grounding Columns.
> > 4.3.2.4   Jumpers, Filter Section.
> > 4.3.2.5   Horizontal Resistors, Filter Section.
> > 4.3.2.6   Vertical Resistors, Filter Section.
> > 4.3.2.7   Capacitors, Filter Section.
> > 4.3.2.8   Semiconductor Devices, Filter Section.
> > 4.3.2.9   Jumpers, Oscillator Section.
> > 4.3.2.10   Horizontal Resistors, Oscillator Section. 4.3.2.11   Vertical Resistors, Oscillator Section.
> > 4.3.2.12   Capacitors, Oscillator Section.
> > 4.3.2.13   Semiconductor Devices and Trim Pots, Oscillator Section.
> > 4.3.2.14   Capacitors on Foil Side of Board.
> > 4.3.2.15   External Connecting Wires.
> > 4.3.2.16   Drilling the Adjustment Screw Access Holes.
> > 4.3.3   Input Buffer and High Pass Filter Board.
> > 4.3.3.1   IC Sockets. 4.3.3.2   Grounding Wire.
> > 4.3.3.3   Column Grounding Wires.
> > 4.3.3.4   Jumper Wires.
> > 4.3.3.5   Resistors.
> > 4.3.3.6   Capacitors on Component Side of Board.
> > 4.3.3.7   Capacitors on Foil Side of Board.
> > 4.3.3.8   Semiconductor Devices.
> > 4.3.3.9   Trimming Potentiometer.
> > 4.3.3.10   External Connecting Wires.
> > 4.3.4   Linear Rectifier and Low Pass Filter.
> > 4.3.4.1   IC Sockets.
> > 4.3.4.2   Grounding Wire and Column Grounds.
> > 4.3.4.3   Jumper Wires.
> > 4.3.4.4   Resistors.
> > 4.3.4.5   A Pair of Diodes.
> > 4.3.4.6   Capacitors on Component Side of Board.
> > 4.3.4.7   Capacitors on Foil Side of Board.
> > 4.3.4.8   Remaining capacitors on component side of board.
> > 4.3.4.9   Semiconductor Devices and Potentiometer.
> > 4.3.4.10   External Connecting Wires.
> > 4.3.5   Linear Mixer and Output Buffer.
> > 4.3.5.1   The Leftover Box.
> > 4.3.5.2   Board Preparation.
> > 4.3.5.3   IC Sockets.
> > 4.3.5.4   Grounding Wires and Capacitors on Foil Side of Board.
> > 4.3.5.5   Jumpers.
> > 4.3.5.6   Resistors.
> > 4.3.5.7   Capacitors.
> > 4.3.5.8   Semiconductor Devices.
> > 4.3.5.9   External Connecting Wires.
> > 4.4   Testing, Adjusting, and Troubleshooting, the Modules.
> > 4.4.1   Low Frequency Generator.
> > 4.4.1.1   Setting Up the Test.
> > 4.4.1.2   Voltage and Current Measurements.
> > 4.4.1.3   Filter Frequency Response.
> > 4.4.1.4   Troubleshooting.
> > 4.4.2   High Frequency Generator.
> > 4.4.2.1   Setting Up the Test.
> > 4.4.2.2   Voltage and Current Measurements.
> > 4.4.2.3   Filter Frequency Response.
> > 4.4.2.4   Troubleshooting.
> > 4.4.3   Input Buffer and High Pass Filter.
> > 4.4.3.1   Setting Up the Test.
> > 4.4.3.2   Voltage and Current Measurements.
> > 4.4.3.3   Filter Frequency Response.
> > 4.4.3.4   Troubleshooting.
> > 4.4.4   Linear Rectifier and Low Pass Filter.
> > 4.4.4.1   Setting Up the Test.
> > 4.4.4.2   Voltage and Current Measurements.
> > 4.4.4.3   Filter Frequency Response.
> > 4.4.4.4   Troubleshooting.
> > 4.4.5   Linear Mixer and Output Buffer.
> > 4.4.5.1   Setting Up the Test.
> > 4.4.5.2   Voltage and Current Measurements.
> > 4.4.5.3   Troubleshooting.
> > 4.5   Chassis Assembly.
> > 4.5.1   Preparing the Panel/Chassis.
> > 4.5.1.1   Drilling the Panel.
> > 4.5.1.2   Front Panel Label.
> > 4.5.2   Preparing the Switches..
> > 4.5.3   Parts Mounting.
> > 4.5.3.1   Mounting the Switches.
> > 4.5.3.2   Mounting the Potentiometers.
> > 4.5.3.3   Mounting the BNC Connectors.
> > 4.5.4   Chassis Wiring Part 1.
> > 4.5.4.1   Power Supply Rectifier and Filter.
> > 4.5.5   Chassis Wiring Part 2, Module Installation.
> > 4.5.6   Power Transformer and 120 Volt Primary Wiring.
> > 4.5.6.1a   If Both Leads Are Solid Black.
> > 4.5.6.1b   If One Lead is Solid Black and the Other One is Black With a Colored Stripe.
> > 4.5.6.2   Line Cord Installation.
> > 4.5.7   Photograph of Finished Product.
> > 4.6   Electrically Bonding the Two Panels.
> > 4.7   The Smoke Test.
> > Chapter 5   Initial Testing, Calibration, and Operation.
> > 5.1 Selecting a Readout Device.
> > 5.2 Initial Tests.
> > 5.2.1 Testing the Signal Source.
> > 5.2.2 Testing the Measuring Circuit.
> > 5.2.3 Checking the Input Attenuator.
> > 5.3 Final Assembly.
> > 5.4 Operating Instructions.
> > 5.5 First Measurement.
> > 5.5.1 Discovery of a Design Mistake.
> > Chapter 6   Calibration.
> > 6.1   Calibration to 0.316 volt = 100%.
> > 6.1.1   Adjusting Trimmer in M 4.
> > 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   Calibration to 1.00 volt = 100%.
> > 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.
> > 7.2   Shooting Trouble.
> > 7.2.1   General.
> > 7.2.2   The Power Supply.
> > 7.2.3   The Signal Source.
> > 7.2.4   The Measuring Circuit.
> > 7.2.5   The Input Attenuator.
> > Chapter 8   A Distortion Reference.
> > 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.
> > 8.2.2 Parts Mounting.
> > 8.2.3 Switch Prewiring.
> > 8.2.4 Switch Label.
> > 8.2.5 Final Assembly.
> > 8.3 Initial Test>
> > 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.