Doepfer A-100 Review *** Part One

From analogueman@delphi.com
Sent Sun, Dec 17th 1995, 12:04

****************************************************************************

Seasonal Greetings Guys,

This is the first part of a personal review of the new System A-100 modular 
from Doepfer GmbH, that I've just taken delivery of. Hopefully it will be of 
some interest to those on the list who may be slightly curious as to what 
the final production modules are like. I should point out to begin with, 
that the A-100 is very much on it's own in this section of the market, and 
doesn't really have any competition, as the only other modular system 
currently being produced commercialy at the moment (Serge, from Sound 
Transform Systems), is undoubtedly the best, and almost untouchable in
terms of what it provides for the sound designer and synthesist. Doepfer 
have seized the oportunity to fill the gap left by the current absence of 
Digisound. This review is of the first batch of modules that have been made 
available, and will continue as and when further batches appear. The modules 
being looked at are as follows:

                        A-110 VCO
                        A-118 NOISE GEN
                        A-120 VCF 1
                        A-130/1 VCA
                        A-138A/B MIXER
                        A-140 ADSR
                        A-145 LFO
                        A-180 MULTIPLES
                        A-100 RACK

The opinions below are, of course purely personal, and I would advise a 
hands-on audition for anyone further interested in the system.

The first thing that I can say is that these modules are far from perfect 
with regards to voltage controlability. Doepfer seem to have wrestled with 
the balance between control and price, and considering the price, I don't 
think that they have done a bad job. They are certainly aware of the initial 
criticisms aimed at the preproduction models, and have made a few changes to 
the first modules, whilst promising to release further modules to address 
them in the near future. It would be very easy to draw upon the bad points 
of the system, but the good ones outweigh these, so to dwell upon them too 
much would be somewhat counterproductave, as new modular gear ain't exactly 
growing on trees at the moment, and Doepfer is a relative newcomer to this 
kind of gear. Serge equipment is considered to be the best of it's kind 
because they have shown they are willing to listen to the people who buy and 
use the synth, and act upon that. Lets see if Doepfer can now do the same.

The first thing that strikes one as you look at the system, is how small
and compact it is. Alarmingly so even. Each module is of the open (Moog 
style) design, with the pcb being held onto the aluminium faceplate by the 
nuts of the front panel sockets, at a 90' angle. They are solidly put 
together, with the soldering on the pcb being done by machine, rather than 
by hand. The few ics that are used are seated in sockets, rather than 
soldered directly onto the board. Conection to the power bus within the rack 
is achieved via a ribbon type cable, with a doubled eight pin female 
connector at each end. These carry the following things;

              gate, cv, +5v, +12v, gnd(x3), and -12v.

The 3.5mm connection sockets on the front are of the type that have an 
internal plastic barrel, so you only need to pull the jack out half way to 
break the connection, helping you not to lose track of what you pulled out 
and where. Final build quality is of a high standard, and as a whole, the 
system looks very good indeed.

         ________________________________________________________

                              A-110 VCO
                              ---------
This is what Doepfer call their standard oscillator. They have a precision 
oscillator comming out early in '96, which is claimed to be more stable, 
with waveforms of a more acurate nature. Not owning an oscilloscope, I 
obviously can't say whether there is anything wrong with the ones put out by 
the A-110, but they sound fine to me. Four waveforms are available, those 
being positive sawtooth, variable pulse, triangle, and sine. All have their 
own output socket. There are two CV input sockets, one of which has has a 
pot to adjust the amount. The other presumably is for the 1 v/oct input from 
keyboards and sequencers etc, although an input from anything would do. The 
pulse width has two input sockets, one fixed, the other variable with it's 
own pot. There is also a dedicated pulse width pot, for manual control. 
Oscillator sync is possible, with a hard sync input socket. Soft sync and 
linear FM inputs will be available on the forthcoming precision oscillator. 
Like all the knobs on this system, the tuning pot is labelled from 0 to 10. 
It has a range of about five semitones. The octave range knob, which is 
smaller than the others, has a range of eight octaves. This knob is a change 
from the prototype module, which had a three position toggle switch. I get 
the feeling, that this was a last minute spec change, as it is only labelled 
as going from -2 to +2, but in reality has five further click stops past +2, 
three of which take you up another octave, until the last two, which pull 
the octaves down about five. Whilst this is in no way a problem, it is 
rather quirky. The module consumes about 70 mA, and is descreatly built, 
with the addition of a couple of TL064CNs, and a CA3046. This is obviously 
the same pcb that they will be using in the forthcoming A-111 precision 
oscillator, as there are labels for linear fm and soft sync printed on the 
component side. The tuning stability isn't the best that I've come across, 
as most modular gear, with the exception of the earliest makes, are usually 
very good. The oscillators certainly need to be tuned every day. Once they 
have been tuned, they tend to stay that way though. I get a feeling that 
whilst these oscillators will shift at quite a rate, judging from e-mail 
I've already received, a lot of people will be waiting for the A-111 to be 
made available. 

         ________________________________________________________

                         A-118 NOISE GENERATOR
                         ---------------------
This is one of the best modules that Doepfer have produced so far. There are 
only three output sockets. White noise, coloured noise, and a random output. 
Two LEDs indicate the +/- of the random output. There is no front panel 
control of the white noise output, but the coloured output has two pots. One 
controlling the "red" level, and the other the "blue" level. The output of  
the blue level, is similar to putting white noise through a highpass filter. 
Lots of the upper frequencies present, and a very clear sound. The output of 
the red level on the other hand is a range of noise with lots of much lower 
frequencies in it, and a much larger sound all together. The ability to mix 
the two together is what makes it special, much better than the inclusion of 
just a pink noise output. The random output has two pots. One for the output 
rate, and the other for the level. The module only uses one chip, a TL064CN.

         ________________________________________________________

                              A-120 VCF 1
                              -----------
"A ladder type, Moog type filter" the advertising blurb said. I do wish that 
synth builders wouldn't keep describing their filters in this way. Ok, so it 
may be built using a totally descreat design, but unless it is actually a 
complete copy, there is no way that it will be like a Moog. And so it goes 
for this one too. To start with, I have to say, that I like this filter. It 
has a warm, fairly precise quality to it. When raised, the resonance causes 
the filter to self oscillate, with the resulting sine wave being fairly 
stable in pitch. It has three CV input sockets, two of which have pots to 
adjust the amount, the other being fixed, for keyboard voltages etc. An 
audio in socket is accompanied with a level pot, along with a single audio 
output socket. Resonance is controlled manually with it's own knob. 
Unfortunately, Doepfer have seen fit to omit a CV input for the resonance. 
This I feel would have made a good solid filter into an excellent one. There 
is certainly room on the front panel for an extra socket, so I can't quite 
work out why they left this out. Especialy when you consider that the next 
three filters from them (A-121,122,123), all have this facility. The pcb 
looks just like filters used to........16 transistors, a handful of 
capasitors, and lots of resistors. All the transistors are 2N3904s, except 
for one 2N3906. From the short time that I've had the system, the filter has 
proved itself to be very adept at producing both gritty hard technotype 
sounds, and large warm smooth type sounds. Personally, I think it's sound, 
whilst being fairly characteristic, does tend to lean a little bit towards 
the old Roland feel rather than the all Amarican Moog, with it's almost 
limitless bottom end. But of course, sound is a very subjective thing, so I 
think that you will either like it or hate it. I like it.

         ________________________________________________________

                              A-130/1 VCA
                              -----------
The VCA comes in two versions. The 130 is the linear type, and the 131 is 
the exponential sort. Their responses are both clean and precise. They have 
two CV input sockets, one of which is fixed, the other has an input level 
pot. There is a gain pot, and two audio input sockets, with coresponding 
level knobs. The single audio output socket has it's own output level pot. 
Internally, the pcb is a fairly simple affair, with three chips, two 
TL062CNs, and a 3381 (a 3382 for the log. module).  

         ________________________________________________________

                             A-138a/b MIXER
                             --------------
These two mixer modules are fairly run of the mill. The A-138a is a linear 
type, and the A138b is a logarithmic one. Both look and behave exactly the 
same, except that the linear one is used for mixing control voltages, whilst 
the other mixes audio. They have four input sockets with matching level 
pots, and an output socket and knob. Internally, they are identical, except 
for different type pots, and both use a single TL062CN. Unless you are 
planning to own a very small system, you are going to need quite a few of 
these, especially the linear ones, as the diminuative size of the modules 
have restricted the number of CV inputs on the panels, these will be 
essential in running the required number of voltages to where you need them.
The output socket on the exponential module gives you the chance to moniter 
the output through headphones, as it accepts a stereo minijack socket 
(ie the sound comes through to both ears rather than one). It's a shame 
there isn't some sort of panning option, but maybe that will be something 
for the near future.

         ________________________________________________________

                               A-140 ADSR
                               ----------
This module has four pots on it. One each for attack, decay, sustain and 
release. It has three output sockets, one of which is an inverse output. 
There is one gate, and one retrigger input socket. There is also an LED, 
which displays a light each time a gate is received. The three position 
toggle switch allows you to vary the time of the output. From left to right, 
it is labelled high, low and medium. Quite why they chose this rather 
strange configuration, I don't know, but it doesn't seem to pose much of a 
problem, and certainly adds to the character of the overall system.
Internally, the module uses two chips. A TL84CN, and a CD4001BCN. The timing 
of this type of module is fairly important, as it effects the sort of uses 
the system will be suitable for. The attack output I have found to be very 
tight, making good basslines and useful percussion sounds very easy. Whether 
other users will agree with that, I've yet to find out, but it's response is 
as good as anything I have at the moment. Doepfer are planning a voltage 
controlled version of this module in the near future. 

         ________________________________________________________

                               A-145 LFO
                               ---------
This LFO is a five waveform module. It outputs a negative and positive 
sawtooth, sine, triangle and square waveforms. The sawtooth waveforms are 
always twice the frequency of the others. There is an LED giving an 
indication of the sawtooth outputs, and one for the sine and triangle. All 
waveforms have their own output sockets. There is one pot for the frequency 
control, and a three position toggle switch controlling the frequency range, 
labelled from left to right, medium, high and low. As on the ADSR, this 
switch is curiously marked. There are plans afoot, to bring out a voltage 
controlled version of this module sometime in '96, that will hopefully give 
the option of using it in the audio domain. Lastly, the module has a reset 
in socket, which resets the waveform every time a trigger/gate is received. 
Internally there are three chips, two TL084CNs, and a CD4053BCN.

         ________________________________________________________

                            A-180 MULTIPLES
                            ---------------
This is an unpowered module, simply giving you multiple outputs from a 
single input. It has eight sockets on the front, and these can be used as 
a one in-seven out, or a dual one in-three out configuration. 

         ________________________________________________________

                              A-100 rack
                              ----------
The racks that hold the modules are solidly built 6U cages, with removable 
rackmount ears. The rack is split in the middle, giving two 3U shelves to 
fit the modules into. The modules themselves are fixed into place using two 
small silver screws on the left hand side of the module, and are held in the 
rack using a holed strip, at the top and bottom. The ventilation is 
excellent, with grid style openings at both the top and bottom. There is a 
fused on/off switch at the back, which I know will annoy some people, who 
will wish to permanantly fix the system into a fixed rack tower. The power 
supply gives out a maximum of 650mA, so if you are considering a high count 
of oscillators (these consume the largest current), a little bit of juggling 
may be called for, so as not to overload the thing. The system is very 
flexible though, and Doepfer can supply you with a second seperate power 
supply unit, if the setup you are planning may breach the maximum output. 
Internally there are two power supply busses, one for each row of modules. 
These are pcb type busses, with connections for fourteen modules each. 

         ________________________________________________________

The only conclusions that I can draw at the moment, are those based on the 
modules that I have at present. I think that the gamble Doepfer has taken in 
producing this system is a bold one, and one that has paid off. Whilst it 
doesn't compete head on with Serge at the top end of the market, it fits 
neatly into the middle, between where Serge is now, and where Digisound used 
to be. I've found it to be an excellent system for those starting out to 
learn subtractive analogue synthesis, and it is also first rate for 
producing high quality sounds. It's not perfect, but nothing Doepfer have 
done up to now is unfixable, and the present modules are a very firm base 
upon which to build a first rate and very usable system.
I've yet to come across either a bad or perfect modular synth, and Doepfers 
example hasn't changed that. Because modular systems are mostly built up 
using the individuals own requirements, the number of criticisms tend to 
vary, and I'm no different. I can't really find any major faults with the 
A-100 at all, only a few minor gripes. But the main point is that despite 
these, it hasn't put me off deciding to build what I already have, into a 
full system. Soundwise it is excellent, operationally it is well laid out, 
and clearly marked, and despite it's small size, is easy to operate and 
experiment with. 

If people find this review to be at all usefull, I will continue, with the 
next batch of modules, due to arrive with me sometime in January. Please 
email me if there are any unanswered questions left out of this retrospect.


Sean.


 ***************************
 *** CONTROL THE VOLTAGE ***
 ***************************

      Sean Coppinger ;-)

  analogueman@delphi.com.uk

 ***************************