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PLUM AUDIO – 

ARBA

  

 

Thanks for purchasing ARBA from Plum Audio! 

 

 

 

 

 

ARBA 

provides four 

Voltage Controlled Amplifiers

 

(VCA)

 with linear response. It may look like a 

simple VCA module but under the hood it is packed with features that unleash a variety of uses. 

 

Three features that distinguish ARBA: 

 

Normalization:

 Everything is normalized to everything – all of the inputs, CV inputs and 

outputs are normalized between the four channels so you can use a variety of 

configurations depending on how you patch it. 

As a result of this feature, you can get a significant gain boost (with CV control!) when you 

chain several channels together. 

 

 

Variable sensitivity:

 Unlike most VCA's in Eurorack that clip easily due to the 5V unity gain 

– the cause of this annoying clipping is that many envelope generators output a standard 

voltage of 8V – with 

ARBA

 you can set the sensitivity of each of the channels (or - how 

much voltage needs to reach the CV input to get unity gain at the output) using the four 

trimmer resistors located on the back of the module. 

 

 

Limiters: 

soft clipping diodes will limit the outputs to 10.2 volts peak-to-peak and warm 

up the sound (the limiters can be disabled using switches on the back of the module). 

 

The combination of these three features allows a variety of uses, for example:

 

Quad simple linear VCAs 

Stereo VCAs 

Summing VCAs 

Soft clipper 

Distortion with CV control 

Level booster (instrument or line level to Eurorack level) 

And much more… 

Summary of Contents for ARBA

Page 1: ...Variable sensitivity Unlike most VCA s in Eurorack that clip easily due to the 5V unity gain the cause of this annoying clipping is that many envelope generators output a standard voltage of 8V with...

Page 2: ...wer bus board The red stripe of the ribbon cable 12V side must be oriented to the same side as the red stripe marking on the header Use the four screws supplied to mount ARBA to a free 18HP space in t...

Page 3: ...age of ARBA is as a quad mono VCA Use one channel to control the level of one mono source Connect the output of the source oscillator filter or any other audio source to the input of this channel conn...

Page 4: ...one CV for two or more channels In the following example ARBA is divided into two sections each of which functions as a stereo VCA The first stereo VCA including channels 1 and 2 CV input of channel...

Page 5: ...ed at the next connected output In this example only the output of channel 4 is used This output sums together the outputs signals of channels 1 2 3 and 4 In this configuration you can also use ARBA a...

Page 6: ...channel 1 is connected This input is shared with the inputs of channels 2 3 and 4 You can connect outputs 1 4 to different paths and use different CV generators to create cool rhythm sequences BOOSTI...

Page 7: ...hard clipping of ARBA is about 23 2V peak to peak 11 6V Be careful ARBA can produce high gains EXAMPLE 5 BOOSTING Connect the audio signal to the input of channel 1 and your envelope signal to the CV...

Page 8: ...of channel 4 and connect it to your listening path Use the CV input of channel 2 to control the amount of distortion When the CV signal on this input is 0V the output is clean Any CV above 0V will inc...

Page 9: ...low the calibration procedure CALIBRATION PROCEDURE First you need to choose what amount of CV will cause unity gain unity gain is the point when the input gain and output gain are equal For super cle...

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