aion LITHIUM Kullanım Kılavuzu - Sayfa 6

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BUILD NOTES

Setting the bias trimmer

As with other BBD choruses, the bias trimmer can be set by ear with no special equipment. Start in the

center position, and adjust to the left or to the right until you hear a modulated chorus signal. Then,

fine-tune it while listening for distortion or other audible artifacts and adjust the trimmer until these are

eliminated or minimized.

You can also connect an oscilloscope to pin 7 or 8 of the BBD and use the scope reading to adjust for

a symmetrical waveform with equal clipping on the top and bottom. Use a signal generator to send an

8kHz sine wave at 2V p-p as a test signal. This is far higher in amplitude than what the BBD would see in

normal operation, but the heavy clipping allows for optimal adjustment.

MN3007 and MN3207 usage

The original Small Clone uses the MN3007 BBD. This BBD is long out of production, but the Xvive

reissues sound just as good and are highly recommended.

The MN3207 replaced the MN3007 in the late 1980s, optimized for lower voltages down to 5V but with

a maximum voltage of 10V. Today, old-stock 3207s are significantly cheaper than old-stock MN3007s,

and the Coolaudio reissues (v3207) are also significantly cheaper than the Xvive MN3007 reissues, so

it's an attractive option.

Importantly, though, the 3207 runs on opposite polarity, so in order for the MN3207 to replace the

MN3007, the supply voltage and ground need to be reversed for the chip.

Some choruses such as the Boss CE-2 can be easily converted to using the MN3207 by setting a few

jumpers to invert the polarity, as in our

Azure

project. We have experimentally included the same

standard MN3007/MN3207 conversion jumpers on the Lithium PCB, although it should be stressed

that we have not tested this and it may be wildly deficient for this circuit. It's possible that the input

biasing network (bias trimmer through R14) would need additional changes in order to work properly.

Therefore, only attempt a MN3207 conversion if you know what you're doing. If we hear reports of

success, then we'll revise the build notes with more confident advice, but for now we are adding a strong

disclaimer to any deviation from the base MN3007 circuit.

Setting the jumpers

Underneath IC2, there are four jumper pads arranged in a square pattern. The MN3007 and MN3207

have their positive and negative supply pins inverted from each other, so the jumpers need to be set to

route the supply voltages to the correct pins.

The underside of the PCB has a legend on the silkscreen showing which way the jumpers should be

soldered. If using a MN3007, both jumpers should be installed horizontally. If using a MN3207 or v3207,

the jumpers should go vertically. If you don't solder these jumpers, there will be no wet signal at all.

If using a MN3207, make sure to use 1N4739A (9.1V zener) for Z1 to limit the BBD's supply voltage to

9V. If using a MN3007, this zener can be omitted since the maximum supply voltage is 15V.

LITHIUM ANALOG CHORUS