DOEPFER System A-100 BBD Module A-188
Contents
1. EPFER System A 100 BBD Module manual CV Out CV1 In Polarity CV1 Delay Clock CV2 In Polarity CV2 Clock Out Clock In Audio In BBD Out BBD Mix Feedback Polarity Mix Polarity Feedback In Mix Out Fig 1 A 188 1 Controls and In Outputs BBD Module A 188 1 1 Introduction Module A 188 1 is a so called Bucket Brigade Device module abbr BBD BBDs have been used to delay audio signals before digital delays dethroned the BBD based effect units But BBDs have some very unique advantages or disadvantages dependent on the point of view over the digital counterpart which result from the special properties of the BBDs BBD circuits can be treated as a chain of Sample amp Hold units S amp H which pass on their voltages to the next S amp H in the chain at each clock pulse A more detailed explanation including the different types of BBDs can be found in the following chapter In any case the sounds generated by module A 188 1 are very special Typical applications are Flanger Chorus Analog Delay or Karplus Strong synthesis But as the A 188 1 has a lot of very unique features voltage controlled clock rate delay time with extreme range polarity switches for the CV inputs feedback and BBD out mix clock and CV output of the high speed VCO BBD clock input feedback insert feedback up to self oscillation a lot of unusual applications can be realized with the module e g delay controlled by ADSR rand2. A Controls and In Outputs 4 1 High Speed VCO Section Delay Clock manual delay control CV1 CV1 input HSVCO Polarity CV1 polarity O CvV2 CV2 input HSVCO Polarity CV2 polarity 2 CV attenuator for CV2 This group of elements is responsible for the clock frequency generated by the high speed VCO HSVCO knob Delay Clock is used to adjust the clock manually Two CV inputs CV1 O CV2 are available to control the clock by external control voltages e g LFO envelope follower random ADSR keyboard CV sequencer theremin ribbon controller foot controller Midi to CV shepard generator The sensitivity of CV1 is approximately 1V oct according to the position of the CV1 polarity switch The diagram on the right side shows the connection between CV1 and clock frequency The straight line represents the perfect 1V oct graph The slightly bended curve is the real behaviour of the HSVCO If an absolutely perfect 1V oct control is required an external precision HSVCO or a VCO with PLL has to be used System A 100 BBD Module A 188 1 BBD High Speed VCO Connection between control voltage and frequency N 3 T Q hee _ Control voltage V Fig 6 relation between CV1 and Clock Frequency Both CV inputs are equipped with polarity switches According to the position of these switches the effect of the corresponding CV is positive i e increasing CV increa
3. A 152 sequencer A 155 theremin A 178 ribbon controller A 198 BBD Module A 188 1 A 133 POL A 188 1 BBD Module Dual VC Polarizer Os12 O 1024 2048 a o Seay ce Out 0 Voltage Controlled Feedback Feedback is processed by an external voltage controlled polarizer A 133 to obtain voltage controlled feedback Instead of the polarizer even a VCA can be used But with a VCA only positive or negative feedback is possible 12 A 119 Ext In A 188 1 BBD Module Ext Input Env Follower 512 O 1024 2048 O 4006 di real in Sanal ev eral Cik Out o Audio In Audio Out DOEPFER QUEPFER Enveloped BBD Control voltage for the A 188 1 is generated by the envelope of the processed audio signal Try positive and negative setting of the CV2 polarity switch and different CV2 levels System A 100 BBD Module A 188 1 A 124 VCF5 A 188 1 BBD Module ma oi Filter Os12 O 1024 Y 2018 Q40 E e ae Ck Out QUEPFER QOEPFER Filtered Feedback The feedback loop is processed by an external filter The example shows an A 124 Wasp filter in the feedback loop But any low pass high pass band pass or notch filter even multiple filters like A 104 or A 127 phasers A 101 3 A 125 or frequency shifter A 126 can be used Especially for the Karplus Strong Synthesis see below a low pass filter is useful in the feedback loop to simulate the natural behaviour of a plugged s
4. Ext FB In The polarity switch controls the polarity of the signal appearing at the socket O BBD Out and consequently the polarity of the feedback signal In the center position of switch the signal at socket BBD Out is off and no feedback is active Consequently the switch can be used to turn on off the feedback effect The polarity of the feedback signal leads to clearly audible different sounds at short delay times For longer delay times analog delay application the sound differences are much smaller for details please refer to page 6 System A 100 BBD Module A 188 1 Knob Feedback adjusts the feedback level In the left ccw position of the knob no feedback or resonance emphasis is added As the knob is turned right clockwise feedback occurs In the fully right cw position the module goes into self oscillation As already mentioned in chapter 2 the result in the self oscillation state depends upon the audio history for details please refer to page 6 Both the self oscillation behaviour and the smoothness of the feedback also depend upon the BBD circuit used in the module 128 256 4096 stages 11 QUEPFER System A 100 Audio In Audio Out Range GUEPFER QUEPFER Standard Flanger Patch Suitable control voltage sources are LFO A 145 as shown in the example A 146 A 147 A 143 3 random voltage A 118 A 149 1 envelope A 140 A 141 A 142 A 143 1 A 143 2 S amp H A 148
5. Strong Synthesis Patch only the 6 oscillators output of the A 117 is used instead of the digital noise output in the basic patch The patch generates a random melody The tempo is defined by the LFO rate the tone range by the N settings of the A 149 1 Manual N and possibly CV N Additional modules can be used e g to modulate N of the A 149 1 or the decay time of a voltage controlled envelope generator e g A 141 or A 142 instead of the A 140 by another random voltage of the A 149 1 15
6. VCAs or VC polarizers or a VC mixer O Mix Out mixed output Mix mix control original BBD Polarity mix polarity This group of elements is responsible for the mixed output appearing at socket O Mix Out In the left ccw position of knob O Mix the original signal appears at socket O In the right cw position of knob the pure BBD signal appears at socket O In the intermediate positions of knob O a mix of these two signals appear at the output socket For a standard flanger effect e g the center position is used 10 DOEPFER The position of the polarity switch O defines if the normal or the inverted BBD signal is mixed to the original signal please refer to page 6 concerning this function Especially for short delay times the position of this switch leads to clearly audible different sounds In the middle position of the switch the BBD share of the mixed signal is off and only the original signal is heard Consequently the switch can be used to turn on off the BBD effect at the mix output O O Ext FB In external feedback input 4 Feedback feedback level control Polarity feedback BBD Out polarity This group of elements is responsible for the feedback functions of the module Socket Ext FB In is the input of the feedback loop and is normalled to socket O BBD Out If an external module is used to control the feedback loop e g a VCA or VC polarizer the module has to be inserted between socket O BBD Out and socket
7. can be used as anti aliasing filter and clock filter If desired one low pass filter can be used behind the audio output to suppress the clock noise when the clock frequency falls below 20 khz Another filter can be used at the audio input to reduce the max frequency of the incoming audio signal consequently reducing aliasing artefacts As the CV output reflects the clock frequency affected by the manual control CV1 and CV2 the external filters automatically follow the clock frequency of the BBD module The higher the slope of the external filter e g 12 24 48 dB octave the better is the clock suppression The HSVCO features a clock output that can be used e g to synchronize two A 188 1 i e both A 188 1 use the same clock source or as high speed clock for other applications e g graphic VCO switched capacitor filter System A 100 BBD Module A 188 1 The clock output of the HSVCO is normalled to the clock input of the BBD section The clock input makes it possible to control the BBD by an external clock source e g another A 188 1 or any other clock signal in the required frequency range For all clock signals from and to the A 188 1 only short patch cables should be used as long cables function as low pass filters for signals above 20kHz A two phase converter generates the two opposite clock signals that are required to drive the BBD circuits The audio input of the BBD module is equipped with an attenuator that enable
8. that can be used as anti aliasing filter and clock filter If desired one low pass filter can be used behind the audio output to suppress the clock noise when the clock frequency falls below 20 khz Another filter can be used at the audio input to reduce the max frequency of the incoming audio signal consequently reducing aliasing artefacts As the CV output reflects the clock frequency affected by the manual control CV1 and CV2 the external filters automatically follow the clock frequency of the BBD module The higher the slope of the external filter e g 12 24 48 dB octave the better is the System A 100 BBD Module A 188 1 clock suppression But the CV output can be used for other applications as well e g controlling parameters of the feedback loop like feedback amount polarity CV of a VCA or VC polarizer used in the feedback loop filter frequency CV of a VCF used in the feedback loop phase shift CV of a VC phaser used in the feedback loop DOEPFER 4 2 BBD Section O Ext Clk In BBD clock input This is the clock input of the BBD section and is internally connected to the clock output of the HSVCO section i e it is normalled to the Clock Out socket O If an external clock source is used the clock output of this source is patched to socket In this case the internal connection to the HSVCO is interrupted The suitable clock frequencies depend upon the BBD used in the module pls refer to the table on page 3
9. to the output socket The combination of these two sockets allows to process the feedback loop with external modules e g a VCA or a VC polarizer for voltage controlled feedback or other modules like filter phaser frequency shifter waveshaper wave multiplier ring modulator or another BBD module for special voltage controlled feedback effects System A 100 BBD Module A 188 1 The polarity of the feedback signal leads to clearly audible different sounds as different frequencies are emphasized or attenuated for positive or negative feedback The feedback can be increased up to self oscillation In contrast to other feedbacks e g filters phasers the result in the self oscillation state depends upon the audio history i e the contents of the BBD when the self oscillation is triggered The reason is that there is not only one possible stable self resonant state for the BBD Any cyclic waveform stored in the BBD is able to resonate provided that the feedback maintains the waveform One can try this out e g with different audio signals e g digital noise and VCO sawtooth as audio input before self oscillation is triggered e g by switching the feedback polarity switch from center position to positive or negative position Different BBD circuits 128 256 512 4096 stages influence a lot of sound parameters Of course the delay time range and consequently the basic sound but even the feedback behaviour both the self oscillatio
10. 00 BBD Module A 188 1 The following table shows the relation between clock frequency delay time and number of stages for some typical BBD circuits Relation between clock frequency kHz and delay time ms BBD circuit number of stages clock frequency BBD clock frequency MN3006 MN3009 MN3004 MN3007 MN3008 MN3005 clock input socket 1 2 clock input MN3206 MN3209 MN3204 MN BL3207 MN BL3208 MN3205 kHz kHz 128 256 512 1024 2048 4096 1 0 5 1024 00 4096 00 2 1 512 00 2048 00 5 25 204 80 819 20 10 5 102 40 409 60 20 10 51 20 204 80 50 25 20 48 81 92 100 50 10 24 40 96 200 100 5 12 20 48 300 150 3 41 13 65 400 200 2 56 10 24 500 250 2 05 8 19 The max clock frequency is 100 kHz only for MN3004 and MN3007 in contrast to 200kHz for MN3204 and MN3207 Remarks The standard versions of the A 188 1 with 1024 and 2048 stages are marked with bold characters The grey italic characters indicate parameters out of the data sheet specifications e g clock frequencies below 10kHz for all BBD devices and clock frequencies beyond 100kHz or 200kHz for certain BBD devices But parameters out of spec may be available with the A 188 1 As the BBD devices cannot be damaged if they are operated with frequencies out of spec we decided to allow such frequencies with the A 188 1 to obtain special audio effects especially for clock frequencies below 10kHz But the regular behaviour is no longer gua
11. The required level for the clock signal is 0 5V levels up to 12V cause no problems This socket can be used e g to synchronize two A 188 1 modules i e using one HSVCO for both modules a b Audio In 3 Level audio input audio input attenuator Sockets Oa and b are the audio input with the assigned attenuator The two sockets are internally connected miniature multiple The second socket can be used to forward the audio input signal to other modules e g to a VCA or VC polarizer or VC mixer for voltage controlled mixing functions Feed the audio signal that has to be processed with the BBD effect into socket Oa or Ob Adjust the Level control so that the output signal does not distort unless you want to obtain distortion For normal A 100 levels e g VCO A 110 distortion appears at about three o clock position of control but the distortion System A 100 BBD Module A 188 1 behaviour depends also upon the BBD circuit used in the module BBD Out BBD output Socket is the raw BBD output i e not mixed not filtered Pay attention that it is affected by polarity switch O Remark The front panel markings of the first two productions series are wrong concerning the BBD Output and the feedback polarity switch Please refer to the scheme on page 4 The BBD output can be used e g for voltage controlled mixing functions i e if the original signal and the BBD signal are mixed externally with
12. ame voltage appears In a BBD the buckets are replaced by capacitors and analog switches As the capacitors of a BBD are very small some pF only even the time required to pass on the input to the output is crucial as the capacitors loose their charges if it takes too long This is why a minimum clock frequency is specified for each BBC circuit Below this frequency the flawless operation of a BBD is not guaranteed In the A 188 1 intentionally frequencies can be used that go below this value to obtain special dirty and crunchy effects BBD circuits are available or rather have been available with different number of stages Usual numbers are 128 256 512 1024 2048 or 4096 stages Currently as of spring 2006 only devices with 1024 and 2048 are still in production Other BBDs are obsolete hard to find and very expensive Therefore only the versions of the A 188 1 with 1024 and 2048 stages are standard products All other versions of the A 188 1 are available only while stocks of the corresponding BBD circuits last The number of stages defines the delay time that corresponds to a certain clock frequency The higher the number of stages the longer is the delay The higher the clock frequency the shorter is the delay Example At 100kHz clock frequency the delay time is 10 24 ms for a BBD with 1024 stages and 20 48 ms for a BBD with 2048 stages DUEPFER System A 1
13. eedback loop all parameters are voltage controlled Even other sound sources 6 oscillators or 2 oscillators of the A 117 noise signal of an A 118 or VCO or only short click of the ADSR can be used For more realistic Karplus Strong applications a filter in the feedback loop can be used see previous page 14 System A 100 DIS NOISE 808 SOURCE A 145 LFO A180 A 149 1 RCV MULTIPLES Quantized Stored Random Voltages 2 oN gt a 0 10 Audoln2 4 In2 Ouipsd 2 gt o 3 7 7 a 4 s o 1 0 y 1 Y Audio O O 2 i BaD ou Polly Mout gt is 7 gt a Conte x E a Jeon lt O Bi Deza Range DOEPFER DOEPFER DDEPFER DOEPFER OUEPFER HUEFFER BBD Module A 188 1 A 131 VCA EXP VCA A 140 ADSR ENVELOPE GEN A 188 1 BBD Module 0512 1024 O 2048 A en Apr cout B R ext FB In goal Karplus Strong Random melody patch A149 1 This patch shows another example for the Karplus Strong synthesis The LFO A 145 is used as clock oscillator but any other clock source could be used as well The rectangle output is connected to the clock input of the Quantized Stored Random Voltages module A 149 1 upper or lower section may be used and to the gate input of the envelope generator A 140 One of the quantized or stored CV outputs of the A 149 1 is patched to the CV1 input of the A 188 1 The rest of the patch is the same as the basic Karplus
14. n and the smoothness of the feedback the distortion behaviour and the output level It is hard to say which is the best solution It depends upon the desired sound bending For typical analog delay sound BBDs with more stages are the better solution But for oppressive flanging sounds caused by short delays or for Karplus Strong synthesis shorter BBDs are recommended System A 100 erview D A 188 1 BBD Module Os O1024 q 2048 E PY y Out i Clock 8 QO Q 8 O Fig 5 A 188 1 front panel Controls Delay Clock 2 CV2 Level Feedback Mix Polarity Polarity Polarity Polarity In Outputs O Clk Out Ext Clk In Ga Audio In 8b Audio In Mix Out CV1 O Cv2 CV Out O Ext FB In BBD Out BBD Module A 188 1 manual delay control attenuator for CV2 audio input attenuator feedback level control mix control original BBD CV 1 polarity CV2 polarity feedback BBD Out polarity mix polarity clock output HSVCO BBD clock input normalled to Clock Out O audio input connected to Ob audio input connected to a mixed output CV1 input HSVCO CV2 input HSVCO CV output HSVCO external feedback input normalled to BBD Out BBD output affected by polarity switch Attention the front panel markings are wrong concerning the BBD Output and the feedback polarity switch Please refer to the scheme on page 4
15. om envelope follower or sequencer with positive or negative effect The A 188 1 also has no built in anti aliasing filter in order not to limit the possibilities of the module For this the CV out is intended DOEPFER 2 Basic Principles As mentioned in the introduction a BBD circuit can be regarded as a chain of Sample amp Hold units S amp H which pass on their voltages to the next S amp H in the chain at each clock pulse From this also the name Bucket Brigade Device is derived as each stage of the BBD can be treated as a bucket At each clock pulse the content of each bucket is forwarded to the next bucket in the chain and the current bucket is filled with the contents of the preceeding bucket EVE UE NAS e Ed Fig 2 Bucket Brigade Remark In reality two buckets are required for each stage as the content of a bucket has to be stored temporarily in a slave bucket before it can be filled with the contents of the preceeding bucket in contrast to a real bucket brigade not the buckets are passed on but only the contents In the BBD the water is replaced by analog voltages which again represent audio signals The first bucket 1 is the audio input the last bucket n is the output of the BBD As in reality there are losses while the water resp System A 100 BBD Module A 188 1 voltage is passed on because some drops of water go wrong and at the end of the chain not the same amount of water resp not exactly the s
16. ranteed especially increasing voltage losses at lower frequencies As the clock frequency falls below 20 khz the clock signal itself will become audible This clock noise can be used as unusual audio source or it can be filtered out with an external low pass filter DUEPFER System A 100 BBD Module A 188 1 ext feedback in feedback oe BBD Out os off neg eedback polarity pos off neg 512 1024 mix polarity Audio In p adder 2048 4096 stage BBD F audio B 8 Audio Out level Mix PL im LTI 2 phase converter ext clock in O clock out manual cu O evi pos off neg CV1 Manual pos offineg CV2 Fig 3 A 188 1 module scheme DUEPFER Fig 3 shows the internal details of the module A 188 1 the upper part is the actual BBD section the lower part the high speed VCO HSVCO The HSVCO generates the clock signal that is required to drive the BBD It has available a manual control and two CV inputs CV1 without attenuator CV2 with attenuator For both CV inputs three position polarity switches negative off positive are available The position of these switches defines if a positive going CV has positive none or negative effect on the clock frequency CV1 has a sensitivity of approximately 1V octave The HSVCO has a CV out available that corresponds to the sum of all CVs manual CV1 and CV2 It s main purpose is to control the CV input of one or two external low pass filters that
17. s to reduce the input level to avoid distortion The audio input signal behind the attenuator is mixed with the feedback signal details below and fed to the audio input of the BBD circuit The audio output of the BBD is processed by an inverter to have both the normal and the inverted BBD output available The reason for this feature is that the polarity is crucial for both the output mixing BBD original and the feedback behaviour of the module The normal output of the BBD and the inverted output are fed to the terminals of two three position polarity switches negative off positive for mixing polarity and feedback polarity The output mixer is used to mix the original signal with the normal or inverted BBD signal The position of the mix polarity switch defines if the normal none or the inverted BBD output is mixed with the original audio signal DOEPFER The following sketch shows the effect of normal inverted mixing by means of a simple sawtooth signal as audio input original TITAN BBD out original delay original delay AAA Fig 4 positive negative mixing of original and BBD signal The center terminal of the feedback polarity switch is connected to the BBD output socket Pay attention that the polarity of this output is affected by the position of the feedback polarity switch especially there is no signal at the output socket if the switch is in the center position The feedback input is normalled
18. ses the clock frequency off or negative i e increasing CV decreases the clock frequency O Clk Out clock output HSVCO This is the clock output of the HSVCO It is internally connected to the clock input of the BBD section The waveform is rectangle with about 3V level The rectangle slopes flatten with increasing frequency and the waveform turns more and more into triangle Even the load on the output has influence to the waveform and level DOEPFER Consequently for all clock patches from and to the A 188 1 only short patch cables 30 cm should be used as long cables function as low pass filters for signals above 20kHz The max frequency at this output depends upon the BBD used in the module and is related to the max clock frequency of the BBD in question pls refer to the table on page 3 It is about 250 kHz for BBDs with 2048 and 4096 stages and about 450kHz for BBDs with 1024 stages and less i e a bit more than the max clock frequency of the specs in the data sheet If the BBD circuit is changed the max frequency has to be re adjusted with a trimming potentiometer on the pc board of the module frequency offset For details please refer to the appendix of this manual CV Out CV output HSVCO This CV output indicates the clock frequency at output and is nothing but the sum of all CV inputs manual CV and CV2 The main purpose of this output is to control the CV input of one or two external low pass filters
19. tring by damping higher frequencies in the decay phase 13 A 188 1 BBD Module Os12 O 1024 Y 204 So fe cy Polarlly Cloc Put Su 2 A 108 VCF8 6 12 24 48d0B Lowpass uts P y Audio Out Audio In y BBD Out pad Max D e 6 DOEPFER DOEPFER Clock Filter The BBD audio output is filtered with a low pass e g A 108 The frequency of the low pass filter follows the BBD clock frequency as the CV output of the module A 188 1 is used to control the frequency of the low pass filter A second filter can be used at the audio input of the A 188 1 to limit the frequency range of the processed audio input signal System A 100 BBD Module A 188 1 A 117 DNG DIG NOISE 808 a an ae VCA A 140 ADSR A 188 1 BBD Module Coo GEN 6512 1024 E2048 C4006 A Cv Dar Clk Out 5 O 4 y Clo TN 2 7 Ea a Le O 2 e vm 9 1 o 10 n V a 7 i 2 6 CV In 6 Oscillators 808 Sound Source 2 Oscillators Gate In Audio Out QUEPFEAR DOEPFER DOEPFER DUEPFER Basic Karplus Strong Synthesis Patch CV and gate are delivered e g by a sequencer ribbon controller Midi to CV interface or Theremin The time parameters of the envelope generator ADSR A 140 and the feedback settings of the A 188 1 define the sound especially the decay time If voltage controlled envelope generator e g A 141 and a VCA or VC polarizer are used to process the f
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