Doepfer A-100 Review *** Part Three ***

From analogueman@delphi.com
Sent Thu, Nov 21st 1996, 11:25

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                                                               21 Nov '96
                                                              ------------

 Greetings Guys,


 Firstly, may I apologize for the delay in the appearance of this review. 
 These modules were ordered some months ago, but disappeared in transit, 
 due to the incompetency of a courier service, who had them sitting in 
 one of their warehouses, about half a mile down the road, for about two 
 months before discovering them again. I swear that if couriers had brains, 
 and brains were gunpowder, they wouldn't have enough to blow their hats off!

 This is the third of an ongoing batch of modules in the A-100 range that I've 
 received, and contains a number of sound shaping devices this time around. 
 As always, I'll list not only what I think of them, but also the ics that 
 they contain, for those interested in the component make up.

 Please note, that I'm in no way connected with Doepfer Musikelektronic GmbH, 
 and that these are purely personal opinions. Doepfer can be contacted on the 
 following (*new address and phone numbers*) :


                          Geiger Str. 13
                          82166
                          Grafelfing
                          Germany.

                Phone:    00 49 89 898 09510

                Fax  :    00 49 89 898 09511


 As always, I would welcome any comments and corrections with regards to 
 this review. 

 A fourth batch of modules should be with me sometime in December, and 
 will contain the new precision oscillators, and the first two vocoder 
 modules.


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                      A-119  Ext. Input/Envelope Follower
                      -----------------------------------

 This module has two socket inputs- a mono 3.5mm and a stereo 1/4" socket. 
 These are labeled Asym.In, and Symm.In respectively. Although you may be 
 injecting a stereo signal into the 1/4" socket, the sound will be a sum 
 of the left and right. There are two identical audio output sockets, with 
 a gain pot for the overall volume control, along with an overload LED should 
 the output signal become too hot. An envelope output socket with an LED 
 indicator is provided along with gate out socket with an associated 
 threshold pot, which also has an LED indicator. As I haven't really had 
 the oportunity to use an envelope generator before (nothing I own has one), 
 I tryed it out by injecting a simple boring sampled kick drum into it, and 
 patched up a sine wave generated from one of the systems filters. I then 
 took the envelope out from the 119 and patched it in to the cv input of the 
 filter and a vca. The result was that I now had a sound of exactly the same
 duration and feel of the original sound, and when mixed together gave 
 something ultimately more usable. I then used the same patch, but also took 
 the gate output, and put that into an envelope generator, which then went 
 into the filters cv input. This gave me a greater control over the filter's 
 response, but with the final sound being triggered at exactly the same time 
 as the external one. Internaly, the A-119 uses two TL064CNs.



                       A-121  12dB/Oct Multimode Filter
                       --------------------------------

 This is the first of three VCFs which uses the 3320 chip from Curtis. 
 Configured as a 12 dB/octave type filter, it has four different and 
 simultanious outputs, each with it's own separate socket on the front. 
 It gives notch, highpass, bandpass, and lowpass outputs and there is a 
 single audio input with a level pot. Apart from a frequency control knob, 
 there are two frequency control voltage input sockets, one of which has 
 an associated attenuation pot. Resonance can be controlled manually, with 
 a pot of it's own, or via an external control voltage, of which there are 
 two socket inputs. One of these has a level pot. Functionally, all four 
 filters give the expected results, but I have to say, that quality wise, 
 this filter really does hit the spot. Whereas the A-120 was slightly 
 disappointing, this one oozes quality. The sound that it passes is both 
 smooth and large from the lowpass output, and does have a slightly 
 familiar feel to it. If someone were to be putting together one of these 
 systems, and were unsure as to which filter to go for first of all, then 
 this would be the one that I would recommend, as the most usable. 
 It uses two pcbs; a small one for the filter ouput sockets, and the 
 main one which seats the single CEM3320 and a TL062CP. There is also 
 three mini turn resistors for scale, offset, and feedthrough. All the 
 pots are 50K, four of which are linear, and one log.



                        A-122  24 dB/Oct Lowpass Filter
                        -------------------------------

 The second of the Curtis chipped filters, this is a straight forward 24 dB/oct 
 configured lowpass type. The audio input socket is accompanied by a level pot, 
 and there are the usual frequency and resonance knobs. There are two cv inputs 
 to control the cutoff level, one of which has an attenuation pot. There is
 also a cv input for controlling the resonance, which is also attenuated via 
 it's own knob. Sound wise, this filter is what I'd call 'typically Curtis'. 
 Nothing unexpected, but solid and very usable, capable of both broad and 
 narrow filtered type sounds. Apart from the 3320, the only other ic it uses 
 is a TL062CN, with a couple of miniturns for offset and scale adjustments.



                       A-123  24 dB/Oct Highpass Filter
                       --------------------------------

 The third of the Curtis chip filters available is a 24 dB/oct highpass. The 
 socket and pot arrangement on the front of the panel is identical to the 
 A-122 (see above). As always, it's always nice to see the implementation of 
 resonance on the highpass filter, with a control volt input to boot. 
 Internally, it is more or less the same as the A-122, with the exception of 
 an additional miniturn, which isn't labelled. 



                            A-125 VC Phase Shifter
                            ----------------------

 This is an interesting sounding module, and great fun to use. It has an audio 
 input socket with a level pot, as does the cv input socket, which controls the 
 phase shift ammount. There is also a dedicated shift knob for manual control. 
 The last two pots control the resonance and mix ammounts, along with an audio 
 out socket. It's a great shame that Doepfer didn't include a cv input for the 
 resonance, as there is room on the front panel for at least a couple of more 
 sockets. The mix knob can be thought of as a wet/dry control, as the signal 
 is uneffected at zero, and a set mix of 50/50 at ten. The resonance control 
 really makes this module, as it's use emphesises certain frequencies within 
 the phased signal that add that 'something extra' to it. The shift itself 
 isn't too dramatic, but enough to enlarge the original signal, with out 
 muddying it. Using the cv inputs to add subtle ammounts of phase shift to 
 a sound, really gives it a polished feel. The pcb is a mass of resistors 
 and capasitors. It uses six BF245 transistors, two TL064CNs, and a TL062CN, 
 along with an offset miniturn.



                           A-128  Fixed Filter Bank
                           ------------------------

 With only two sockets, an audio in and out, the rest of the panel is taken up 
 with fifteen pots, each with an assigned frequency. The fixed frequencies 
 that it effects are-

        50, 75, 110, 150, 220, 350, 500, 750 Hz,
        1.1, 1.6, 2.2, 3.6, 5.2, 7.5, 11.0 KHz.

 Whilst nothing more than a knobbly graphic equaliser, this is rather usefull 
 for removing certain frequencies from a sound, from time to time. A resonant 
 filter bank would have undoubtedly been much more usefull, but Doepfer may 
 well have one planned for the future. The module has threee identical pcbs 
 inside, each one for five of the pots, and each holding three TL064CNs, with 
 differing value capasitors for the various frequency bands. 
 


                          A-148  Dual Sample & Hold
                          -------------------------

 This is a simple and basic sample and hold, with two per module. Each one has 
 a trigger and a sample in, and a S&H outpot socket. There also are a couple 
 of leds displaying +/- control for the output signal. Internally, each S&H 
 uses a MC14053BCP, and a TL064CN.



                           A-150  Dual VC Switches
                           -----------------------

 This is an amazingly simple but highly effective and usefull module to have. 
 Each vc switch has four sockets: a control volt input, an input/output 1 & 2, 
 and an output/input socket. The I/O 1 and I/IO 2 have an led indicator each. 
 As the name suggests, by applying a control voltage of less than -3.6v, the 
 input of I/O 1 is routed to the O/I socket, and when a cv of more than +3.6v 
 is applied, then the input of I/O 2 is routed. As an example of it's use, by 
 patching a square wave into the first input, and a sawtooth into the second, 
 and using the square wave as the cv switching source aswell, you will have 
 a waveform at the output that consists of a single cycle of each of the 
 two inputed waveforms. Controlled switching between two different filter 
 types is also great fun. Although I haven't yet tried it, I understand 
 that the sockets are bidirectional, which in practice should mean that 
 a signal put into the O/I socket can be switched to either of the other 
 two. The pcb uses a BC549, and a MC14053BCP IC for each of the two 
 switches.  



                       A-191  Midi-CV/Shepard Generator
                       --------------------------------
 
 I'm going to hang back on my opinions on this module for a while. You see, 
 it was originally advertised as a straight forward Shepard Generator, which 
 to put it simply, is a device which generates a number of modulating 
 waveforms, triangle for example, each of which is slightly out of phase with 
 the last, giving rise to the possibility of infinitely rising filters etc. 
 But since ordering them, Doepfer have drastically changed the spec, adding a 
 midi input, allowing such delights as the ability to sync the waveforms to 
 midi, and enabelling the module to output midi controllers from the output 
 sockets, such as #01 (mod. wheel), #05 (portmento), #10 (pan) etc. 
 Unfortunately, as the module has a digital side of it, which requires 
 operating via a push button system, and the only documentation currently 
 supplied with it is in German, it's going to take me a little while to get 
 my head fully around the damn thing. (If there are any German speaking 
 friends out there who own one, and could email me a summery of the nineteen 
 page manual, I would be most grateful). Externally, it has sixteen output 
 sockets, five push buttons, three LEDs, and a midi input socket. Internally, 
 it has an eprom, an Intel 8052 processor, two 5628CNs, a TLC272IP, a 
 DM74LS573N, a H4C509, and a 9526, and is all contained on two pcbs. This 
 module, as the forthcoming A-190 midi-cv module, requires a five volt supply, 
 unlike the rest of the system, which uses plus/minus twelve.



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 There are no new forthcoming modules to report on at present, with the 
 exception of three utility type ones, which should be available at the end 
 of this year. These are-


             A-176  CV Source -  Provides 3 manally adjustable CVs, 
                                 2 of which have an additional fine 
                                 control pot (for precise tuning of 
                                 a VCOs frequency etc).

             A-177  ECM -        An interface for the connection of 
                                 external controllers such as a foot 
                                 pedal etc

             A-179  BAC -        The Bus Access Module provides access 
                                 to the system-bus. It also will have 
                                 'signal refreshing' amplifiers for 
                                 use when in connection to more than 
                                 one rack frame.


 I should have another batch of modules with me sometime in December, which 
 will include the new A-111 high end oscillators, and the first two vocoder 
 modules. I'll hopefully post Part Four to the lists before Christmas, 
 depending upon when they arrive. 



 Until then, chow  :)



 Sean.
 
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