doepfer System A - 100 VCA A-130 / A-131 1. Introduction VCA-LIN.
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1. is in direct linear proportion to the control voltage input see Fig 1 The A 131 has an exponential or logarithmic re sponse That means that control voltage changes have less effect at low levels of amplification than at high levels and makes the A 131 more sensitive and sui table for subtle changes at low levels see Fig 1 Amplification 5 10 Control Voltage Fig 1 Response curves for the A 130 and A 131 System A 100 VCA A 130 A 131 1 Gain This controls the overall gain of the VCA At 0 with no control voltage present there is no amplification at all no signal is present at the VCA s output Once the gain control is turned up amplification occurs even if there is no CV input present The gain control shifts the whole VCA response upwards see Fig 2 P 10 E 5 Control Voltage Amplification Fig 2 Effect of gain control on VCA response A 130 A 131 VCA System A 100 doepfer H Note that if a control voltage is partially nega tive for instance an LFO modulating the VCA you need to set the VCA gain above zero since otherwise the input signal is only ampli fied when the modulation CV is positive see Fig 3 Input RARE Gain gt o aA Output cv SFX cain 0 4 Fig 3 VCA output level at different gain settings 2 CV2 This attenuator affects the level of voltage control at socket It controls the amount of effect the CV has on amplificati2. ation frequency in the audio range side bands occur like those produced by FM Frequency Modulation and interesting timbres emerge A 130 VCA LIN Fig 5 VCA amplitude modulation with an LFO System A 100 doepfer Modulation depth is adjusted with control 2 Fig 6 shows a way of voltage controlling this modula tion depth using another VCA In this example the VCAs have the following functions e VCA 1 A 130 AM control e VCA 2 A 131 total volume control e VCA 3 A 130 modulation depth control The voltage control input A to the modulation depth VCA can come from an ADSR MIDI controller etc Fig 6 AM with voltage controlled modulation depth doepfer System A 100 VCA A 130 A 131 Keyboard control of VCA tracking You can use the CV output from a keyboard to modu late the VCA and so have level of amplification de termined by the pitch of a note what s usually cal led keyboard tracking To produce the opposite effect that is inverse keyboard tracking where lower sounds are more amplified than higher ones patch a Voltage Inverter A 175 in before VCA 2 see Fig 8 Set the gain control 1 at maximum and use CV2 In the example in Fig 7 high frequency notes are control 2 to determine the intensity of the effect amplified more than low frequency notes Use control 1 on VCA 2 to vary the degree of keyboard tracking mf p Fig 8 amp Inverted keyboard tracking the higher t
3. doepfer v1 A 130 VCA LIN Audio Out System A 100 VCA A 130 A 131 1 Introduction Modules A 130 Linear VCA and A 131 Exp VCA provide voltage controlled amplification H This section of the manual applies equally to the A 130 and A 131 because apart from the one difference of their response curves they are otherwise identical For audio signals you would normally use the exponen tial VCA A 131 and for control voltages the linear VCA A 130 It doesn t always have to be that way though The amount of amplification the VCAs provide is deter mined by the voltage at the CV input and the position of the gain control which sets the overall gain in the system The VCA has two audio inputs each with an attenua tor They are amplified by an amount determined by the combination of the gain and the two CV controls A 130 A 131 VCA System A 100 doepfer 2 VCA overview Controls 1 Gain Overall gain control A 130 VCA LIN 2 CV2 CV attenuator for input 3 IN 1 Attenuator for audio input 4 IN2 Attenuator for audio input 5 Out Attenuator for the output signal a In Outputs 1 CV 1 Control voltage input CV2 ditto with attenuator Audio In 1 Audio input n Audio In 2 ditto Audio Out Audio output for the combined audio signals input at and and then amplified by the VCA doepfer 3 Controls The A 130 has a linear response the amplification
4. he pitch the less amplification Fig 7 Keyboard tracking the higher the pitch the louder the output A 130 A 131 VCA 6 Patch Sheet The following diagrams of the module can help you recall your own Patches They re designed so that a complete 19 rack of modules will fit onto an A4 sheet of paper Photocopy this page and cut out the pictures of this and your other modules You can then stick them onto another piece of paper and create a diagram of your own system Make multiple copies of your composite diagram and use them for remembering good patches and set ups P Draw in patchleads with colored pens e Draw or write control settings in the little white circles System A 100 A 130 VCA LIN cv1 10 Audio In 1 Q 0 10 Audio In 2 o Om 0 10 Audio Out doepfer A 131 VCA EXP Audio In 1 oO 0 10 Audio In2 OC 0 10 Audio Out Qo 0 10
5. on 3 IN1 4 IN2 Attenuators 3 and 4 control the level of the signals input into the VCA H If the output signal distorts in an unwanted way turn down the input level using control 3 and or 4 5 Out This attenuator controls the total volume of the VCA s output doepfer 4 In Outputs CV1 CV2 Sockets and are control voltage inputs whose voltages are combined The effective range of the VCA goes from 0 V no amplification to 5 V maximum amplification AudiolIni AudiolIn2 The signals you wish to amplify are input through audio inputs and or Audio Out The output signal here is the audio inputs amplified by the VCA System A 100 VCA A 130 A 131 5 User examples Typical voltage controlled amplification A standard VCA patch is shown in Fig 4 An ADSR envelope produces a time dependent amplification curve which can affect any sound source you choose The curve can be very quick with a fast envelope or it can produce long slow changes in the volume of a sound A 131 VCA EXP Fig 4 Time dependent amplification using an ADSR A 130 A 131 VCA Amplitude modulation In Fig 5 an LFO is modulating an A 130 linear VCA with Gain gt 0 so that the amplification changes cyclically with the LFO s voltage Amplitude modu lation AM With an LFO frequency in the sub audio range 1 Hz to around 15 Hz the result is Tremolo see Fig 5 With a modul
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