NEA NEA 5F4019 VCA Build Notes and User Manual free download

File name NEA_5F4019_VCA_Build_Notes_and_User_Manual.pdf

NEA-4019 Discrete VCA User Manual & Build Notes Thank you for purchasing an NEA-4019 VCA module. This module is an adaptation of the ARP 4019 VCA found in the ARP 2600 synthesizer using . This document will provide information about the basic functions of the module, build notes, as well as the trimming procedure. Power The red stripe on the power cable is always -12V. Be aware of the orientation of this cable. The cable and the PCB header are keyed to avoid accidentally plugging the power cable in backwards. The VCA has a red LED indicator on the rear PCB to indicate that the module has successfully powered up. If you do not see this LED lighting up, there is a problem and you should disconnect power immediately. Front Panel Jacks Audio Input 1 & 2 - These are the signal inputs of the VCA. Although they are labeled as audio inputs, DC signals can be amplified as well. There may be slight DC offsets when using the VCA to amplify DC signals. Audio input 1 in non-inverting, and audio input 2 is inverting. Linear CV Input - This jack is a VCA CV input that has a linear response. Linear CV gain is typically slightly less than that of the exponential CV input. Ideally a 0-8V signal should be fed into this input. Exponential CV Input - This jack is a VCA CV input converts incoming CVs into an exponential response curve. This input is useful for percussive, snappy envelopes. Ideally a 0-8V signal should be fed into this input. The exponential CV input is capable of higher gains than the linear CV input. They can be made equal by reducing the EXP GAIN trimmer, but it can also sometimes be useful to have more volume output. Audio Output - This jack is the output of the VCA. Front Panel Controls Audio Input 1 & 2 - These two knobs attenuate the incoming signals plugged into the Audio Input 1 & 2 jacks. Linear CV Amount - This knob attenuates incoming CV signals fed into the Linear CV Input jack. Exp CV Amount - This knob attenuates incoming CV signals fed into the Exp CV Input jack. VCA Gain - This knob controls the master gain of the VCA. Trimmers The NEA-4019 has 4 trimmers on the PCB. The trimmer functions are as follows: Exp Gain Trimmer - This trimmer sets the maximum gain of the Exp CV Input. Note that the OFFSET ADJ trimmer also affects the Exp gain. This trimmer should be set so that there is maximum volume and minimum thump. This trimmer is normally set between 6:00 and 11:00 Offset Adjust Trimmer - This trimmer sets the maximum gain of the whole VCA. The 4019 does have some CV offset. This DC offset becomes greater as this trimmer is increased. Note that the OFFSET ADJ trimmer also affects the Linear gain and Exp gain. If you hear any CV bleed, try reducing this slightly. This trimmer is normally set between 7:00 and 12:00. Lin Gain Trimmer - This trimmer sets the maximum gain of the Linear CV Input. Note that the OFFSET ADJ trimmer also affects the Linear gain and Exp gain. This trimmer can be set fully counter-clockwise unless t