“Simple single tube preamplifier with tone control that includes options for adjusting the bass, midrange, and treble frequencies.
A vacuum tube preamplifier is typically used to amplify the signal from a microphone, musical instrument, or other audio source before it is sent to a power amplifier or recording device. Compared to solid-state preamps, vacuum tube preamps are known for their warm, natural sound and ability to add harmonics and distortion that can enhance the perceived “musicality” of the audio signal. They also have a unique “saturation” effect that can add a pleasing “tube warmth” to the sound.
This time I will present you how to make a simple single tube preamplifier with tone control that includes options for adjusting the bass, midrange, and treble frequencies. It also has gain, volume, and input sensitivity controls.
The heart of the device is ECH83 which is a low voltage vacuum tube works with only 12 V anode supply, used especially for car radios. Instead of ECH83, we can use ECH81 tube without any modifications.
The circuit has been presented on several audio forums, and I specifically followed the instructions on the engel-sound blog, where you can also find other tube projects, and everything is neatly drawn and described.
The preamplifier is relatively simple to build, and in addition to the vacuum tube it contains several resistors and capacitors as well as five potentiometers.”