- ページ 7

ミュージックペダル aion AURUMのPDF マニュアルをオンラインで閲覧またはダウンロードできます。aion AURUM 12 ページ。 Based on boss od-2 turbo overdrive

BUILD NOTES, CONT.

OD-2 / OD-2r differences

The OD-2r is an updated version of the OD-2 that was released in 1994, nine years after the original

OD-2. The major feature was the addition of the "remote" jack allowing the channel to be changed with

an external footswitch. While BOSS did not mention any other changes when marketing the new unit,

they did sneak in a few updates internally and the two units do not sound exactly the same.

First, there's an added two-transistor volume recovery stage so that the unit has more volume available.

The original OD-2 barely got to unity gain at max volume—a persistent complaint from users—but the

added volume recovery solves this issue entirely.

Second, the tone control capacitor has been increased from 22n to 27n. This allows for slightly more

treble cut at the minimum setting, but with the treble control set high, it makes essentially no difference.

Third, a minimum drive resistor has been added in series with the drive control. This is largely

responsible for the OD-2r's perception of having slightly more gain than the original, although it really

just impacts the knob positions and the gain itself is not increased.

Fourth, the supply voltage for the Turbo stage has been increased from 5.6V to 7.6V by changing the Z1

zener from 6.2V to 8.2V.

Lastly, the bias voltage is different. While the original OD-2 had a trimmer for the Turbo mode's bias

voltage, the OD-2r omits this and just uses fixed resistors. It's not known what parameters they used

in the OD-2 to determine where to set the trimmer in the factory, but the nominal 2.6V bias voltage in

the schematic is less than half of the 5.6V supply, so it's may have been as simple as setting the trimmer

to 2.6V. However, if it was performance-based with 2.6V being just a rough target, then we don't have

enough information. We only know this trimmed voltage wasn't important enough to keep in the OD-2r.

The improvements in the OD-2r make it the definitive version of the circuit, and it's recommended to

build the Aurum to OD-2r specs, which is the default configuration in the parts list.

Building the original OD-2

If you want to build a straight OD-2, make the following changes.

1. Use 22n for C12 instead of 27n.

2. Jumper R8 instead of using a 4k7 resistor.

3. Use 1N4735A for Z1 (6.2V zener) instead of 1N4738A.

4. Use 16k for R36 and 14k for R37, which will give 2.6V bias from a 5.6V source.

5. Run a wire from the middle pin of the Tone control to pin 3 of the Volume control, and omit all of

the components in between: C13-C15, R21-26, and Q8-9. No traces need to be cut, just leave the

spaces empty.

This list is provided for completion's sake, but since the volume recovery stage fixes a severe

shortcoming and does not color the tone, it's recommended to skip #5 and keep this added stage in an

OD-2 build.

AURUM AMP OVERDRIVE