Aion Electronics AURORA Manual - Page 6

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BUILD NOTES

The Q6 Mod

One little-known modification to the Ross/Dyna circuit is to change the output section so it takes its

signal from a different place in the envelope detector. By doing this, you eliminate the ripple on the

compressed signal which is heard as a slight distortion. It's a vast improvement on the original circuit

without changing the characteristic of the tone.

The default configuration of the Aurora is to use this Q6 mod. However, if you do want to build a fully-

stock Ross or Dyna Comp, you can use a 47n film capacitor for CX1 and omit R22-24 and Q6.

The C17 Mod

One way of getting a little more "snappiness" to the circuit is to use a 1n capacitor for C17 to bypass the

R25 resistor. This will give a slight increase in treble content above 3kHz at the output of the effect. You

can increase this value to lower the frequency. For example, 1.5n will increase the treble above 2.2kHz.

Release Control

The default configuration of the Aurora includes a "Release" control which is adapted from the Boss CS-

2. (Boss called it "Attack", which is not entirely wrong, but it's more accurate to say that it controls the

release at the decay of the signal rather than the attack at the beginning.) When the pot is turned all the

way down, it's the stock Ross/Dyna circuit.

The optimal pot value for this is 150k reverse audio (antilog) taper, but this value has to be custom-

ordered and none of the DIY parts suppliers have it in the right-angle type. Instead, this project uses a

more common 500kB (linear) pot with parallel resistors to drop the value down to 150k and change the

taper to mimic reverse audio.

The one side effect of this is that the pot can't get all the way to zero like a normal pot. As a result, the

R18 resistor (normally 10k) has been decreased to 100R.

If you are using a true 150kC pot, you'll need to jumper R19 and change R18 to 10k. Omit R20 entirely.

Treble Switch

The Treble switch is adapted from the Janglebox. The Janglebox actually omits C10 entirely so there's

no treble attenuation after the OTA, but after testing out a number of different combinations, it felt

best to have at least a very small capacitor connected at all times. These three capacitor values (180pF,

330pF and 820pF) are the ones that were chosen after testing. With the switch in the "up" position,

the result is the stock value of 1n. The "down" position is 510pF (a bit of treble boost) and the center

position is 180pF (a bit more treble boost).

AURORA COMPRESSOR/SUSTAINER