Vermes
Advanced Member level 4
This tube preamplifier is equipped with three functions. It has a pure timbre – the device was inspired by classic applications of Fender and preamplifier Grooves Tube Trio, booster with potentiometer control of volume (switchable) and buffer allowing you to send signal to long distances without losing its quality. The system has a very efficient, three-way, active correction of the timbre based on preamplifier Ibanez TK999HT. The main advantages of that project are high sensitivity, almost noiseless operation and very good quality of sound.
Circuit of the preamplifier and three separate stabilized power supplies were mounted on a PCB. Anode voltage uses Zener diodes (150V+100V in series), glow – by stabilizer L78L12, transistors and chip using TL7824. Using diode 1N4007 between the ground and medium output of the stabilizer at the output of glow power supply, you gain voltage of 12,6V, which is fed to heaters of tubes 6N2P-EV, connected in series.
The system has outputs for two LEDs. LED1 indicates power supply turned on, and LED2 indicated BOOST mode, which can be switched by a two-sections, bistable switch (one section is plugged into placed marked as SW and another in series with LED2).
2,2kohm potentiometer smoothly sets the threshold of volume change in BOOST mode.
If the booster function does not require 2,2kohm in the place of potentiometer, you can use a vertically placed 1,5kohm resistor, and leave the medium output of the potentiometer free and add a 22uF capacitor directly to the cathode of the tube using a plus. You should also remove 27kohm resistor, and use a jumper instead of SW switch.
Stabilizer in L78L12 requires a heat sink. To reduce hum, all the signal cables (also potentiometer cables) should be shielded. The tube is installed in slot NOVAL 18mm for print. You need to solder the glow power supply paths (current 300mA). Red lines in the diagram represent the jumpers. The PCB is prepared in two versions (normal and mirror). Mounting diagram is the view from the elements. Images of the PCB in the doc. file are dimensioned.
Link to original thread (useful attachment) - Lampowy preamp do gitary z aktywną korekcją Ibanez TK999HT