We featured the 13-Pin Input Breakout module last week as a great option to interface a Roland GK compatible guitar with the Eurorack Modular environment.
In part II, let's focus on the options for this module, namely, the maximum gain of the seven low-noise amplifiers. When ordering this module, one can select one of three gain options: 20dB, 30dB, or 40dB. These correspond to amplification factors of 10x, 30x, and 100x (adjustable from zero to maximum. So which one do you chose?
That depends on how you intend to use the module:
A) Feeding the GK string and guitar audio into a module that expects guitar-level signals, such as the SynQuaNon ATG module or a pedal I/O, for example. In this use case, little amplification or even attenuation is advisable and the 20dB gain option will be fine.
B) Feeding the GK string and guitar audio into a module that expects +/-5V signals, typical of most Eurorack modules. This requires approximately 30x or 30dB amplification.
C) Feeding the GK string and guitar audio into a module that expects +/-10V signals. This can be accomplished with the 100x or 40dB amplification option. One interesting side benefit is that this amplifier can be driven into mild clipping and add distortion to the signal if desired.
Keep in mind that there is a trade-off between maximum amplification and noise - the higher gain amplifiers, despite using low-noise opamps, will exhibit higher noise levels, albeit only noticeable at high volume levels.
Lastly, all three amplifiers can be configured to be attenuators, with gains of zero to one. This is done by placing the 7 jumpers on the back on the left side of the gain selection header. More on this next week when we discuss the 13-Pin Output Breakout module!