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A-108

1. System A 100 6 12 24 48 dB Low Pass A 108 Audio Level 4 ry Audio gt A 108 gt CV 1 CV 2 lt gt CV2 Freq gt L CV 3 lt x gt m CV3 Res Feedb 6dB 12dB 24dB 48dB BP LP LP LP LP Y f Y f J e 1 Introduction Module A 108 is a completely new unigue voltage controlled low pass band pass filter based on the well known transistor ladder Moog ladder The module has internally an 8 stage low pass filter with different slopes available 6 12 18 24 30 36 42 and 48 dB per octave In the factory the outputs with 6 12 24 and 48 dB are connected to the four low pass sockets at the front panel In addition it features an band pass output i e band pass with transistor lad der The module has manual controls for frequency and resonance available Resonance can be adjusted right up to self oscillation in which case the filter will behave like a sine wave oscillator Three CV inputs for frequency control are available Two of them are eqipped with attenuators The A 108 features an external feedback input that enables the insertion of additional modules into the feedback path The audio input is very sensitive so that distortion is possible even with normal A 100 levels A 108 6 12 24 48 dB Low Pass 2 VCF 8 Overview 6 12 24 48 dB Lowpass Ouputs BP CV 1 o e 6db LP
2. e i le ie Fig 3 Filter response curves middle resonance Fig 4 Filter response curves high resonance For all figures Band pass a b 48 dB Low pass Gi 24 dB Low pass d e emmeli unu 12 dB Low pass 6 dB Low pass 18Hz 166H2 1 KHZ 10KHZ 4 In Outputs Audio In This is the filters audio input socket Patch in the output from any sound source eg VCO noise gene rator subharmonic oscillator sampler mixer output OBP e 6dbLP gt e 48db LP The sockets are the filter outputs with the filter types band pass BP as well as 6 12 24 and 48 dB low pass LP IS You may change the factory settings of the cut off slopes 6 12 24 48 db for the four low pass outputs see chapter 6 for details CV1 CV2 CV3 The sockets CV1 CV2 and CV3 are control voltage inputs to control the filter frequency Input CV1 has no attenuator and works approximately to the 1V octave standard not as exactly as the VCOs Inputs CV2 and CV3 are equipped with the attenuators and so that the sensitivity of these inputs can be adju sted With attenuators set to 10 fully clockwise the sensitivity for CV2 and CV3 is about 0 5V octave System A 100 6 12 24 48 dB Low Pass A 108 If you patch one or more modulation sources e g LFO ADSR Random S amp H Theremin Ribbon MIDI to CV to these inputs the cut off frequency of the filter will be modulated by the sum of the control voltages
3. The patch in fig 5 has these control inputs available e Char Mod filter cut off slope e Freq Mod 1 filter frequency 1 e g ADSR s Freq Mod 2 filter frequency 2 e g LFO If the 48dB low pass output of the A 108 is connected to the feedback input of the A 108 through a VCA even the resonance is voltage controlled control voltage of the VCA DHE FER System A MC VC Mixer CV Out gt i Audio In Char 1 e wen 1 CV 1 Mod CV s ext t re O Me a lt ext 3 l GV 3 3 lt ext 4 iy 4 Audio Out SP GSS Di Audio Joystick we T Out III t Fig 5 Low pass filter with voltage controlled cut off slope 100 6 12 24 48 dB Low Pass A 108 lt e e A lt ZN lt e U e 100 Hz 1 kHz 10 kHz A 108 VCF 8 6dB LP 12dB LP 24dB 48dB LP Feedb i Audio Level N Audio In Freq Mod 1 Freq Mod 2 A 108 6 12 24 48 dB Low Pass 6 Changing the assignment of the four low pass outputs Only 4 output stages are available as this seems to be sufficient from our experience In the factory the 4 outputs are connected to the filter stages with 6 12 24 and 48 dB cut off slope This is a well considered compromise as these outputs generate audible diffe rent sounds E g the audible difference between the 48d
4. have to be made with wires two by two instead of the jumpers The upper row of the pin headers are the 8 filter stage outputs in pairs The lower row of the pin headers lead to the inputs of the 4 output stages in pairs whereby the pins below 6 db belong to out 1 the pins below 12 and 18 to out 2 the pins below 24 30 and 36 to out 3 and the pins below 42 and 48 to out 4 For details please refer to the A 100 service manual additional charge 6 12 24 48 dB Low Pass A 108 42 48 dB 30 36 dB System A 100 18 24 dB 6 12 dB BOARD A 1 08 6712724 48dB LOW BAND DOEPFER A 100 SYSTEM m Ee g IC6 TLO84 R24 22k Lsls Ls ls 107 TL084 L P La EH m a EE Ra 3k3 MED R33 18k e pee c12 SAD c5 c z l 220u O 22u 18u ild n Jiri output 4 output 3 output 2 output 1 A 108 6 12 24 48 dB Low Pass System 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 sm e Draw in patchleads with colored pens Draw or write control sett
5. B and 42dB or between 42dB and 36dB is very little So it would make not much sense to have 30 36 42 and 48 dB available instead of 6 12 24 and 48 dB But if desired any of the 8 filter stages can be connec ted to one of the 4 outputs By changing the internal connections jumpers or wires each filter stage is available but only four at a time Even a multi way switch could be used but from our results the factory setting 6 12 24 48dB is the best combination for mu sical applications The factory settings can be changed if the correspon ding jumpers on the pc board are removed and re arranged for the desired new output combination On the pc board 4 double row pin headers are avai lable see picture on next page The positions of the jumpers on these pin headers determine the assign 8 System A 100 QDHEP FER ment of the filter stages to the outputs One pair of jumpers is responsible for each of the filter stages The factory setting of the jumpers is marked black These are the possible jumper settings the factory settings are printed bold e Output 1 only 6 dB possible e Output 2 12 dB or 18 dB e Output 3 24 dB or 30 dB or 36 dB e Output 4 42 dB or 48 dB In principle each filter stage can be connected to one of the four output stages but this would require additio nal wiring and cannot be carried out by changing the jumper settings only e g 18 dB to output 3 All combinations not listed above
6. CV2 e e 12dbLP CV3 Audio 24dbLP in VCF 8 Freg o 0 10 am CV3 0 10 System A 100 Controls Freq CV2 CV3 Audio Level Emph In Outputs Audio In BP 6dbLP CV 1 CV 2 CV 3 Feedb Manual frequency control Attenuator for frequency control voltage at input CV2 Attenuator for frequency control voltage at input CV3 Attenuator for audio input Resonance control Audio input to the filter 48 db LP Filter outputs Control voltage input for frequency control approx 1V Oct Control voltage input for frequency control level controlled by Control voltage input for frequency control level controlled by external feedback input for reso nance audio input DUEPFERB P 3 Controls Freq Control is used to adjust the filter frequency manu ally i e the middle frequency Tu for the band pass resp the cut off frequency f for the low pass see fig 1 IS The actual filter frequency results from the sum of the manual control and the external control inputs CV1 CV3 CV2 e Z CV3 For voltage control or modulation of the cut off fre quency the CV inputs can be used The controls and act as attenuators for the inputs CV2 and CV3 to adjust the control voltage level Audio Level This attenuator is used to control the amount of s
7. i e the sound color changes according to the sum of the control voltages put out by the modula tors am If you use the VCF as a sine wave oscillator it is recommended to connect the pitch CV to socket CV1 as this input works approximately to the 1V octave standard Do the same if you want the filter s cut off frequency to track ex actly with the pitch of a note Feedb Module A 108 has available an external audio input for resonance This socket is normalled i e it is connected to the 48 dB low pass output unless another signal is patched into this socket Different modules can be inserted into the feedback loop see chapter 5 for examples E g inserting a VCA enables voltage controlled resonance It is also possible to feed back other filter outputs than the 48 dB low pass to obtain another resonance behaviour A 108 6 12 24 48 dB Low Pass 5 User Examples The filter s cut off frequency can be modulated in various ways e g ADSR A 140 A 141 A 142 LFO A 145 A 146 A 147 Sample amp Hold A 148 Ran dom A 118 Joy Stick A 174 Theremin A 178 Ribbon A 198 or via MIDI A 190 A 191 Many of these examples can be found in the manuals of the other filters of the A 100 system One special feature of the A 108 is the external feedback input This enables the insertion of any audio processing module into the feedback path In serting a VCA leads to voltage controlled resonance In this case the contr
8. ignal entering the filter audio input If the filters output distorts turn this control down unless you deliberately want the distorted sound as a special effect The filter audio input is very sensitive so that distortion is possi ble even with normal A 100 levels Distortion appears about from position 5 with normal A 100 audio levels System A 100 6 12 24 48 dB Low Pass A 108 Freq Out a Ta Out E K a Emph E L aK Emph oo fu Freq Freg Fig 1 Frequency response of band and low pass Emph Control is used to adjust the filters resonance or emphasis the parameter which emphasises the fre quencies around the cut off point f For the band pass this control changes the bandwidth see Fig 1 4 Close to its maximum setting the filter becomes so resonant that it goes into self oscillation and starts behaving like a sine wave You can take advantage of this effect and use the VCF as an additional sine oscillator Self oscillation will break off at high distortion levels as the internal feedback signal is drown out by the distorted audio signal This feature may intentio nally be used to create new sounds If you want to use the filter as a sine wave oscillator no audio signal should be fed in or control to zero A 108 6 12 24 48 dB Low Pass System A 100 QOEPFER r F 18Hz 166H2 1 0KHZ 16KH2 18Hz 166HZ 1 0KHZ 16KH2 Fig 2 Filter response curves minimal resonance
9. ings in the little white circles IPH ED ECD A 100 QOEP FER 6 12 24 48 dB Lowpass 6 12 24 48 dB Lowpass Ouputs Ouputs eR BY 1 x Freq lt B SA Freq e e o s 0 10 dp LP CV2 Weve 6dbLP GV 2 awa e e e j 0 10 One 12dbLP CV3 Zana 12db LP CV3 NT Audio o JD Audio G w 24dbLP n Audio 24dbLP in Audio Ar ON Level ra Level e e e 0 10 RL O 48db LP Feedb Emph 48db LP Feedb Emph ee J e L T DT
10. ol voltage of the VCA works as voltage control input for the filters resonance Other modules that are suitable for insertion are e g phaser A 125 frequency shifter A 126 waveform proces sor distortion A 116 A 136 or even other filters Another example is a filter with voltage controlled cut off slope in combination with the voltage control led mixer A 135 and the morphing controller A 144 Fig 5 shows the corresponding patch The four low pass outputs 6 12 24 48 dB of the A 108 are connected to the four audio inputs of the voltage controlled mixer A 135 System A 100 QHEP FER The levels of the four mixer paths are controlled by the control voltages coming from the morphing controller A 144 The audio output signal of the filter with voltage controlled cut off slope is available at the output of the voltage controlled mixer A 135 The control voltage that is used to control the cut off slope is connected to the control voltage input of the morphing controller A 144 That way it is possible to sweep the cut off slope from 6 48dB fig 5 with the control voltage applied to the CV input of the A 144 In the example the voltage is generated by a joy stick A 174 and called character modulation Of course any other control voltage e g LFO ADSR MIDI to CV Theremin Random could be used to control the character i e the cut off slope For more examples please refer to the A 144 user s manual

A-108

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