Transistor Selection
The transistor selection process is a very important aspect of any pedal build, but is particularly crucial where Germanium devices are used. The first stage of the selection process is to determine Hfe and leakage figures for the devices in hand, and from this information, any transistors that fall outside of pre-defined limits are set aside for other projects. In recent years, a useful instrument called a Peak Semiconductor Component Analyser (pictured) has become available, and this greatly speeds up the selection process.
Using the Peak Atlas DCA to measure transistor parameters
Having short-listed some likely candidates based on measured performance, the next stage is to actually listen to them. The transistors are inserted into a device which replicates the circuit of the pedal being produced. (The photo below shows some transistors being tested for use in a VPW MkII circuit). A guitar and amplifier are then used to listen to the short-listed transistors, swapping and changing them until I’m happy that they are the best possible choices for the build in question.
Initial audio test for transistors to be used in a MkII circuit
The selected transistors are then soldered into place in the final circuit. On completion, every pedal is tested again to ensure consistent results, and to check for proper operation.
MkII and Mk1.5 circuit boards awaiting transistors
All this takes time, and cannot be rushed without compromising the quality of the final product. The results speak for themselves – every pedal leaving the Vintage Pedal Workshop is a fine-sounding example of it’s type, and consistency between individual examples is as good as it possibly can be, given the inherent variability of the Germanium transistors used.
The finished item!