This workshop on tube or valve audio amplifier design in three parts is presented by Menno van der Veen, MSc, a world-renowned specialist of valve amplifier design. He presents techniques for enhancing valve or tube amplifiers. The masterclass is aimed at anyone seeking in-depth information on the operation of these amplifiers.

The masterclass starts with a short discussion of the classic approach using valve load line graphs, followed by current sources and current fold-back techniques.

Next, the negative effect of cathode electrolytics is covered as well as reducing supply voltage interference.

With the help of state of the art measurement techniques the (in)correctness of feedback is proven, while also clarifying what's happening deep inside the core of the output transformer.

This discussion allows the pleasant sound reproduction of valve amplifiers to be substantiated in detail.

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Part 1: Preamplifiers

• Traditional approach - advantages and disadvantages
• Effects of coupling and decoupling capacitors
• Modern approach with a constant current source; designs
• Causes of distortion in the constant current source
• Impedance converter function and implementation
• Cathode decoupling, yes or no?
• Folded cascode to avoid signal currents on the ground rail
• Eliminating supply interference
• Sources of additional information

   

Part 2: Power Amplifiers

• Function of the output transformer; basic rules
• Output amplifier circuits (the project)
• Disadvantages of cathode capacitors in SE amplifiers
• Disadvantages of cathode capacitors in balanced amplifiers; remedies

   

Part 3: Measurements on valve Amplifiers

• Looking into the black box: informative measurements on the outside
• Measuring output impedance versus frequency
• Measuring gain linearity versus frequency and input voltage; insight into micro detail reproduction by the output transformer
• Which types of distortion are acceptable, and which are not?