This repository contains schematic and layout for the Alembic F2b preamp.
This project took its inspiration from:
- https://the7line.clan.su/publ/diystompbox/alembic_f2b/2-1-0-58
- https://the7line.clan.su/publ/diystompbox/bass_tube_preamp_alembik_bassman/2-1-0-38.
All the following section is based on the Alembic_F2b_bass_preamp_schema.pdf schematic.
Input:
- 12VDC @ ~310mA
- ~150mA is used for 12AX7/ECC83 heater
True by using SW1 footswitch.
R200 and C200 are used to smooth the switch.
R5 is the grid-stopper along with C0 the Miller capacitance (R5+C0 forms a low-pass filter that atenuate frequencies greater than ~34KHz).
Resource: http://www.valvewizard.co.uk/gridstopper.html
First stage is composed R1, C1, R3 and C3.
Second stage is composed R2, C2, R4 and C9 that can saturate when the Gain's pot is at its maximum.
Resources:
- http://www.valvewizard.co.uk/gainstage.html
- https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/ for
C1andC2 - http://www.learningaboutelectronics.com/Articles/What-is-a-coupling-capacitor for
C3,C9andC10
Fender like tone stack: C5, C6, C7, Bass, Midrange and Treble.
C8 is used as bright mod.
Sweep is used to move the mid freqs but it also changes the behaviour of bass and treble pots, default is 0% (100KΩ).
Resource: http://www.guitarscience.net/tsc/fender.htm
R200 is the input impedance for instrument.
R7 is the grid leak.
This part of the schema is juste used to reduce the output impedance.
R9 and R10 divides the HT voltage by 2 and put the AC signal provided by C9 oscillating around 110VDC.
Q1 is just used as a cathode folower, no amplification is done, we just use the low impedance property of the transistor.
C100, L1 and C101 are used to filter the voltage and current in order to minimize the hum provided by the heater.
If your power supply has a good quality, this part is not needed.
Resource: http://www.valvewizard.co.uk/heater.html