aion Nereus Manuale - Pagina 5

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BUILD NOTES

Setting the bias trimmer

The bias trimmer sets the voltage at the base of Q3. Assuming a 9.6V supply voltage, the trimmer's

range is 3.06V to 3.88V. We're not sure how Catalinbread determined the optimum setting, but in

the unit we traced, the trimmer was set to 21.5k (21% rotation), which would be 3.26V. Feel free to

experiment and see if you notice any significant difference, but otherwise just set it to that position and

forget about it.

Volume knob rotation

The original Octapussy has a knob labeled "Attenuation", which is nothing more than a reversed volume

knob that reduces the output as it's turned up. We have reversed this in the Nereus so it acts as a

traditional volume control.

Transistor substitutions

The Octapussy uses PN2222A transistors, which are a TO-92 version of the 2N2222A (TO-18 metal

can). This is a low/medium-gain NPN transistor that is almost identical to the 2N3904, which can be

substituted with no change in tone.

The "A" suffix designates higher maximum voltage and temperature, but the electrical properties are

otherwise is identical between the two versions. The non-"A" PN2222 is

available from Aion

FX.

Resistor substitutions

The original circuit used carbon composition resistors for R3 and R7. This type of resistor is notorious

for drifting over time. We measured these two resistors in the unit we traced and found that the 15k

resistor (R7) measured 17.1k, and the 150k resistor (R3) measured 159.8k. Both are 5% tolerance, but

R7 is 14% above nominal and R3 is +6.5%.

We do not recommend using carbon comp resistors when building this circuit, but if you want to

replicate the sound of the unit we traced, you can use a 17k metal film resistor for R7 and a 160k metal

film resistor for R3, which are the nearest precision values.

Electrolytic vs. film capacitors

The original Octapussy uses 2.2uF electrolytic capacitors for C9 and C10. We try to avoid electrolytics

in the signal path where possible, so the PCB layout uses non-polar film caps. However, if you do want to

use electrolytics as in the original, the polarity has been marked on the PCB. Otherwise, these polarity

marks can be ignored.

NEREUS OCTAVE FUZZ