Sunday, February 27, 2011

A-101-2 Vactrol Low Pass Gate

I must say i am very happy with my latest module, the A-101-2 Vactrol Low Pass Gate.
This module is a combination of a 12dB Low-Pass Filter and a Voltage Controlled Amplifier (VCA), with 2 vactrols as controlling elements with very unique characteristics and is very popular amongst the members of the Doepfer A-100 Yahoo Users Group.

The module is based on the Buchla Model 292 Quad Voltage-Controlled Lopass Gate module. '
The term "Low Pass Gate" was first used by Don Buchla for a module that can be switched between Low-Pass and VCA.
Buchla's current (2004) update is the Model 292e Quad Dynamics Manager ,that is functionally identical to the older model, but includes some extra functions like velocity inputs, allowing controllers to control note volumes with performance gestures and preset storage.

Doepfer's LPG module can handle 2 different incoming control voltages that can be used to control the Low-Pass filter, or to open or close the VCA.
Additionally a combined mode LP + VCA is available which makes the sound more dull as the loudness decreases. This is characteristic of all acoustic instruments (the harder you strike, pluck, or bow, the richer the overtone structure), but had been lacking in electronic instrumentation before..

In contrast to the Buchla design the A-101-2 offers attenuators for both CV and audio input, a manual resonance control and two gate inputs to control the function of the module in addition to the manual toggle switch.
The filter is hard to describe, but vactrols are known for their smooth sound behavior. Compared to a 'normal' 12 dB filter like the Low-Pass filter from the A-121, they sound quite the same, but the Vactrol inside the A-101-2 does give it a smoother edge that can perhaps best be compared with a very subtle 'slew' effect. The VCA has that same 'slewy' characteristic, but doesn't sound dramatically different than a regular VCA to my ears.

The combination of the LPG and VCA, is (obviously) my favorite setting and with the resonance up this module really starts to shine. ( Resonance is adjustable all the way up to self-oscillation )
A nice extra are the 2 Gate inputs, that can make you ( rhythmically ) switch between the two functions of the module with an external sequencer or other triggers. I'm not sure if 2 Gate inputs was necessary though.., personally i had rather seen an extra CV input for the Resonance (QCV) for example.
(Perhaps this can be modified?)

Overall this is a very nice-sounding module, that i will use a lot in the near future. I'm not sure if i put it in my top-5 list of favorite modules, but it will at least be in my top 10 for the next few months.

- Check my earlier Vactrol Basics post for more general details about vactrols,
or take a  look at Doepfer's Vactrol Basics page.
More about the A-101-2 LPG  including an audio example at Andreas Krebs blog

Thursday, February 24, 2011

Analogue-Systems-to-Doepfer Adaptors

Ever thought of installing Analogue Systems modules in your Doepfer Eurorack (or the other way around) without much trouble?

Tony from Synovatron came up with a few nifty solutions for that;
His latest 'inventions' are small adapters that allow you to simply plug directly into your  AS or Doepfer module, or that fit the connector on the module's PCB.

Installing is as easy as it looks;
 Note the red stripe - just line up the Doepfer cable's red stripe with it.
 The adaptors are also marked with pin 1 and have an orientation mark so pin 1 goes to the top (in fact to pin 1) and the red stripe goes at the bottom.

The order code for the socket-to-socket version (left) will be ASM2DB Adaptor (or Analogue Systems Module to Doepfer Bus Adaptor). The code for the plug-to-plug version (at the right) will be DM2ASB Adaptor (or Doepfer Module to Analogue Systems Bus Adaptor).

More info at

Monday, February 21, 2011

Vactrol Basics

A Vactol is an opto-isolator device that is often used for channel-switching in many modern amplifiers, but these electronic parts can be used in various other ways too, for example in synth-modules like Doepfer's A-101 Series and the A-102 Low Pass Gate module.
There are many kinds of optical isolators, but the most common is the LED/photo-transistor type.

A vactrol is a combination of a light depending resistor (LDR) and light source (LED) both put into a small 100% light-proof case.
The principle of a Vactrol is very simple.
When an input current is applied to the LED, the output phototransistor turns on.
The only connection between the LED and phototransistor is through light -not electricity, thus the term optical isolator. 
These optical isolators are primarily digital in nature with fast response times suitable for interfacing with logic gates. Rise and fall times of a few microseconds, faster for some isolators, are typical.

So together, the coupled pair act as an electrically variable potentiometer.
Since the output element of the AOI is a resistor, the voltage applied to this output resistor may be DC and/or AC and the magnitude may be as low as zero or as high as the maximum voltage rating.
Because the input will control the magnitude of a complex waveform in a proportional manner, this type of isolator can be used as an analog control element in all kind of ways in analog synthesizers.

Find a review of my A-101-2 Vactol Low Pass Gate module  HERE

More info on Vactrols:   Doepfer Vactrol Basics page
                                      Vactrols on Wikipedia
                                      PDF via

Friday, February 18, 2011

Arranging Modules

Like most of you all know i recently installed my 4th metal G6 frame.
It was about time that i did that, because i already had a few modules that didn't fit the old rack and that were lying loose in a drawer.
After installing the new frame i came up with the idea of this blogpost.

Of course i had to re-arrange my modules again... The old layout just didn't make any sense anymore. Some modules were so weirdly placed that patching them always resulted in a whole spaghetti of cables.
I couldn't find many guidelines for arranging modules on the web, so I just started and made a few notes during the process.

A few of my personal guidelines that work the best for me are:
-    Before you start, disconnect all racks from the power supply! Safety first!
-    Work from top to bottom. I'd almost say work from top left to bottom right. That will keep the system and the flow of signals much more 'readable'
( I'm not sure if this works for Arabic countries, where they read from right to left though... )
-    Try to keep all your multiples on the left side and the Mixers on the right side. I love distributing signals from the sides up and/or down first before i patch a new sound. This avoids cable-cluttering and keeps the overall look 'clean'.
-    Group the modules, eg: Sound Sources / Filters / VCA's / Mixers / Modifiers / Modulation sources / Switches and Sequencers / Clock/Gate/Digital Modules / Voltage Sources / Auxiliary and Special Modules
-    Keep modules that you often use in combination close to each-other ( see my PatchPierre BFF section )
-    Read the manuals of the modules regarding power consumption of each module, and make sure your busboard can handle all the modules that are connected in that row. - note that some require an additional +5V power supply with 50mA e.g. the low-cost 5V adapter - don't forget where you placed it.

-    Check the manuals again for other module-specific requirements. ( some modules should not be placed next to certain others, to avoid interference )
For example don't place oscillators next to a power supply and keep the distance between the Theremin modules at least 30 centimeters etc.
-    Working with colored cables and/or switches does help improving the readability of your system. Too bad Doepfer only sells a few colors in fixed lengths. Longer black and yellow plus shorter red and blue cables would be appreciated. Purple and orange cables too ( personally )
-    Don't forget to fill up the open spaces with blind-panels for safety and EMC reasons. ( ... i knew there was something missing in that first picture )

Okay... everyone has his own preferences on how to arrange their system, this was just a personal (short-) list of the things that i could think of at the moment.
Please leave some feedback if you have any suggestions. I might include more tips later.

Tuesday, February 15, 2011

Quick Tip V : Solving Jack Socket Contact Problems

Some ( minor ) contact-problems have been reported with the older mini-jack sockets ( S6PC, manufacturer: Cliff / England ) that were used by a variety of manufacturers of electronic equipment.
Unfortunately Doeper also used these sockets in their earlier modules, so these problems can happen with your module too, if yours was made before the end of 2002. 

The 3.5 mm miniature jack sockets used in the A-100 system before about 2002 have been very sensitive to the diameter and shape of the jack plugs of the cables used to interconnect the modules.
If you have contact problems with older modules Doepfer advices the following procedure:
  • Disconnect the A-100 system from mains due to safety reasons
  • Remove the module from the rack and disconnect the bus cable if necessary
  • Insert the jack plug into the socket causing contact problems
  • Press down the hollow of the "hot" contact very carefully using a slotted screwdriver (see picture at the right)
  • This should lead to a good contact between jack plug and jack socket
  • If the result is not good enough repeat the procedure without inserted plug but pay attention that the upper contact spring does not slip below the lower one. Use the screwdriver very carefully !
  • Connect the bus cable to the A-100 bus board (if removed)
  • Assemble the module into the A-100 frame
  • Connect the A-100 system to mains and turn the system on
  • Now the contact problem should no longer occur
  • P.S. Since 2003 a new type of jack sockets with stronger springs and so-called "curly rear contacts" is used in the A-100.
Source: Doepfer FAQ

Update February 17 - Nice follow-up at the Synovatron blog

Saturday, February 12, 2011

Quotes V : Alan Pearlman

"The electronic instrument's value is chiefly as a novelty. With greater attention on the part of the engineer to the needs of the musician, the day may not be too remote when the electronic instrument may take its place ... as a versatile, powerful, and expressive instrument."

Alan Pearlman wrote this in 1948... 21 years later he founded ARP Instruments Inc.

Wednesday, February 09, 2011

Most Wanted IV - A-157 8x16 Step Trigger Sequencer

At NAMM 2010 in Anaheim USA, Doepfer showed a very early prototype of the A-157 8 x 16 Step Trigger Sequencer. There's not much information available about this module, besides the info in the NAMM 2010 News PDF on the Doepfer site. Even Doepfer's own Future/New Modules section doesn't have any info on it.

What we do know ( about the prototype(s) ) is that it will be a 'simple' and affordable trigger sequencer (only 8x8 steps, no preset management).
The final module will be equipped with assigned LEDs (arranged in 8 rows with 16 steps each), 8 trigger outputs and clock/start/stop/reset inputs.
It generates 8 trigger signals that are set by the buttons. The LEDs are used to show the active steps and the external control signals clock, start/stop and reset are used to sync the unit to other A-100 modules (or via suitable interfaces to Midi/USB).

An additional preset management will be added to the final version of the module. At the time Doepfer was also thinking about a low cost version of this module with an 8x16 or 8x32 display (like the left unit in the picture) but with only one row of buttons that had to be assigned to one of the rows in question.
The expected date of delivery of summer 2010 was never made.

In fact i haven't found anything more on the web or in the forums about this module, what the reactions were, or a new expected release date.
They are probably still working hard on perfecting the module. The module shown at NAMM wasn't even finished but did give a nice insight on what they are working on.
I like the idea and layout of the front-panel, but personally i prefer my Clock and Reset inputs at the left side of a module, i guess they will at least change that in the final product.

I'd love to have one in a near future, programming rhythmical stuff will become much easier with a module like this, looking forward owning one, but i am afraid i have to wait a while...

Sunday, February 06, 2011

Booktip VI - The Museum of Synthesizer Technology by Martin J. Newcomb

Okay... the cover-design of this book isn't outstanding, but the content is in fact very interesting.
This book, simply called The Museum of Synthesizer Technology, written by Martin J. Newcomb in July 1994 shows the huge collection of what used to be the Museum of Synthesizer Technology that was situated in a  part of Berkshire, UK.

The museum, opened by Bob Moog, only existed for a few years ( 1994 - 1997 ) and was at the time the largest collection of analogue synthesizers in the world.
The idea was nice; the aim was to preserve all these analog synthesizers for future generations, and today's generation would be helped by exhibiting them and by keeping the (service- and normal) manuals available for the public.

Basically the book ( A4-sized, 118 pages ) is an overview of the museum's collection, with a lot of large (color-) pictures and accompanied by well-written background-information on the different synth-companies and types.
...most of all i like it for it's pictures...

Not included with the book, but there was also an interesting video out about this museum with uncut demonstrations, that was published in 2006 by Analogue Heaven, called Analogue Heaven The Museum of Synthesizer Technology. It is a revised release of the original museum-video, but including some extras.
Find the 65 minute documentary HERE (in six parts)
or HERE (full version)

The book has no ISBN number.

Thursday, February 03, 2011

Racks, Cases and Monsterbases

In the beginning it was easy; you only had a few choices:
You could either buy a 3-unit high rack (A-100G3), a 6-unit high rack (A-100G6) or the 6-unit high suitcase version (A-100P6) from Doepfer to mount and organize all your A-100 modules.
Nowadays you can choose from a huge variety of other housings from Doepfer, from 32HP width miniature-cases up to 168HP monster-cases.
You can even make your own cases/cabinets with the low-cost DIY-kits containing rails, a power supply and bus-boards.

The most economic versions nowadays are the low-cost plain wood cases (A-100LC6/LC9) ,which cost about 35% less than the metal and standard suitcase versions.
If that is not your thing you can always go for the monster-cases;
Twice the usable width of a 'normal' rack, but finished with a black or grey finish in a flightcase-look are available in many different shapes and sizes.
There's even a monster-base that fits under these cases, with 2 rows of 168HP width, one with horizontal alignment and a second with a 45 degrees inclined row.

- note from the Doepfer-site: " ...the 12U monster cases are a bit difficult to handle by one person only "

I recently ordered my 4th metal G6 case because i already owned three of them that are filled up to the max. I already have some loose modules lying around that i would love to have back in my system again.
Budget-wise i wanted to go for the LC9-version(s), but then i had to re-arrange the rest of my system too, to give it a same look. Too much work for now.

For my next expansion i am considering building myself a cabinet, using 5 or 6 A-100DIY1 kits
That is probably by far the most in-expensive way. If i sell my G6-cases second-hand, i will probably even have some money left to buy me an extra module or two. We'll see...

Tuesday, February 01, 2011

A-136 Distortion / Waveshaper

The A-136 Distortion/Waveshaper module is a nice distortion/wave-shaping module with external CV control possibilities. It can be used for audio-distortion, but also to modify control voltages ( create new control waveforms made from LFO, ADSR, or Random voltages ) with it.

The module divides the incoming signal into 3 different components; the positive, the negative and the original signal. The 5 knobs and the 2 CV inputs let you adjust the positive and negative amplification and the clipping levels.

With all the different different settings you can create complex wave-shapes and impressive sounds, but to be fair, i have heard better (extended?) distortions. This might perhaps be the reason why Doepfer advices you to use it in combination with filters... not sure though...

For mild and subtle distortions this module sounds alright, but the wilder, clipping distortions are a bit too extreme for me.
Personally i prefer the A-137 Wave Multiplier or the A-116 WP Waveform Processor controlled by random voltages, for the more interesting ( subtle and extremer ) wave-shaping.