aion CYGNUS Podręcznik - Strona 7

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BUILD NOTES, CONT.

Resistors & diodes in the first clipping stage (G-2 only)

The G-2 was

first traced in 2009

other than the resistors mentioned above, there is no reason to doubt its accuracy.

However, with thousands of people building clones based on the schematic in the years since, it's

become apparent that the choice of diodes in the first gain stage is very important. The G-2 uses

germanium diodes, which are notoriously inexact and have a wide variance in forward voltage even

among the same part number. Germanium diodes usually have forward voltages from 0.2V to 0.4V, with

some types going even higher or lower.

If the diodes have too low of a forward voltage, the transistor's gain is not high enough to keep up and as

a result it will not distort the signal like it should. There are three solutions to this potential issue:

1. Use germanium diodes with a forward voltage above ~0.3V. (No testing has been done to see where

the cutoff is, so you might be able to go slightly lower or you may need to go even higher.)

2. Use BAT41 diodes (silicon Schottky) instead of germanium. These have a forward voltage of around

0.4V which is more than enough.

3. Increase the gain of the previous stage by using an 18k resistor for R18 and 100R for R19.

Since #3 is the simplest and most universal solution, the parts list for the G-2 variant has been updated

to use these values by default. If you'd like to try #1 or #2, though, you should use the original Cornish

values of 15k for R18 and 680R for R19.

The P-2 does not have this issue since it uses silicon clipping diodes and has higher gain throughout.

Tone modifications (G-2 only)

The G-2 is known for having significantly more low-end than a standard Big Muff circuit, and this can

sometimes be too much in a live setting depending on the mix.

If you want to keep most of the G-2's character but cut the bass, try omitting C20 (the G-2's 22uF

capacitor in the last stage) and instead using C26 (the P-2's 10n capacitor). This is responsible for a lot of

the bass-heaviness, and that single change will go a long way. It's also recommended to reduce the input

capacitor (C1) to 100n.

Transistor substitutions

The BC549C (G-2) and BC550C (P-2) are interchangeable with no difference in sound, so either can be

used. If you want to substitute a different transistor, you'll want one with very high hFE, in the 600s.

The PCB layout uses the B-C-E transistor pinout, which is the opposite of the E-B-C convention used by

transistors with a "2N" prefix such as the 2N3904. The closest substitute in this series is the 2N5089. If

using these, rotate them 180 degrees. Use a multimeter to check the pinout if you're not sure.

The transistor outlines also include a rectangular collector pad above the "B" and "E" pins so that a SMD

transistor such as the BC849C can be used.

CYGNUS DISTORTION/SUSTAINER

by Dirk Hendrik for freestompboxes.org. The trace was thorough, and