A-170 Dual Slew Limiter

I mentioned my A-170 Dual Slew Limiter earlier in a few BFF posts, but so far i never took the time to write a separate blogpost about it. Until now that is...

The A-170 Dual Slew Limiter consists of  two separate slew limiters, also known as portamento controllers or integrators.
In electronics, the slew rate represents the maximum rate of change of a signal at any point in a circuit. Just like a Glide circuitry, it flattens or smoothes the incoming signal.

The top section of the module is the 'simplest' of the two Slew Limiters, with one joint control, which sets both rise and fall times (from approx. 0 ...10 sec).

For precision voltage control this one is recommended, but version One (before May 2009 / check your version number on the module's PCB) had a small voltage drop that was caused by the protection resistor at the A-170 output.

( check Doepfer's solutions for that HERE ) 

A-170 modules after May 2009 don't have this voltage loss.

The second Slew Limiter has separate controls for rise and fall times, and you can set the overall range (high/low/medium) for these parameters with a three-position switch. 

Because the diodes in the lower Slew Limiter are voltage-dependant, there is a voltage off-set of around 0.5 V.  This naturally makes it unsuitable for precise 1Volt- per-octave work, but for simple voltage control this is no problem at all.

Not only is the lower Slew Generator suitable for pitch-CV's, you can alternatively use this one as a simple AR (attack/release) envelope generator (works with any gate/trigger or LFO).
Very useful if you don't have enough envelope generators and want some punchy or percussive basslines.

Also worth reading: Wikipedia Current Limiting

Quotes VIII : Karlheinz Stockhausen

" ...being quiet and meditating on sound is something completely different and will be discovered very soon by a lot of people who feel that the visual world doesn't reach their soul anymore. "

Karlheinz Stockhausen - Composer
( 22 August 1928 – 5 December 2007 )

DIY A-180 2 x 4 Multiples Module

Unwired DIY A-180

Okay... Maybe not my smartest DIY-project, but at least i tried;
In one of my earlier posts about Doepfer's pre-punched blindplates i stated that you can easily make your own A-180 Multiples module, and save yourself a little bit of money by making your own.

That last thing is correct; it does save you some money (even a bit more if you shop around for components), but if you count the time putting the parts together you can ask yourself if it was also worth your precious time.

I did order a few of the 4HP width blindplates (punched for 8 socket / identical to A-180 front panel but without printing) and also ordered a bunch of sockets from Doepfer and just had to give it a try.

Mounting the jack sockets was simple though the pre-punched holes. Because i wanted it to be a 2 x 4 multiple i thought it would be smart to turn the both sets of 4 multiples in a different way for easy wiring and a certain balance. (but not really necessary)
The wiring was a bit harder. it's not easy to solder very short wires, especially for a beginner like me. It took ages for me to solder all the sockets together, but i finally got it together and the end result works fine. Be sure you leave no exposed wires on the back, a passive module like the A-180 cannot cause lot of electrical damage but can cause audio or CV 'leakage'.

But... was it worth the 10 Euro's that i  saved by buying the loose components?
For me it just wasn't, but i can image with even cheaper components and connectors or a piece of breadboard instead of soldered wires it might work for you.
Because i still have another pre-punched A-180 blindpanel i will also make the other one.

Not only to work on my soldering skills, but in my opinion you never have enough multiples.

The A-180 front panel without printing is available as a spare part. It can also be used for other DIY modules, for example as a connection unit for other modules that have to be controlled by the universal vactrol module A-101-9 .

Most Wanted - Future Modules Update

It is always good to keep an eye on the posts from the Doepfer Yahoo Usergroup.
Not only to get answer to all the A-100 questions you have, the DIY-tips, and the interesting module discussions but also for Dieter Doepfer's own input, troubleshooting and the occasional company updates.
In one of his latest posts he announced a few interesting 'new' things on Doepfer's to-do list, including a few that are not yet on Doepfer's Future Module page.

The ones you can already find on that page are the A-190-5 polyphonic USB/Midi-to-CV/Gate interface, the A-142-4 Quad Decay, A-195-1 Pitch-to-CV/Midi/USB interface, A-192-2 CV/Gate to Midi interface, A-143-4 Quad VCO/VCLFO and the A-100 touch keyboard.

The original A-126(-1)

I already blogged about the forthcoming A-157 Trigger Sequencer (not much info on the Doepfer site, only in a NAMM 2010 brochure), but the update of the A-126 module was new for me.
The A-126-2 Frequency Shifter II will be a redesign of the old module. 

Because of availability of the special circuit CEM3382 used in the original module's internal quadrature VCO, the 'original' A-126 is no longer available and they had to stop the production of this module. 

It looks like Doepfer is now working hard on a succeeding model without an internal VCO.

Other modules that were mentioned were a VC Slope Generator ( no specs or further info available, but maybe something like the Serge Universal Slope Generator ?- i'm only guessing !), a Master Clock module/synced LFO, the A-100 bus board V2 with some Analoge Systems connectors ( no more Analogue Systems-to-Doepfer adaptors necessary? ), and an A-100 miniature power supply redesign 

Besides that, Dieter posted that they are also still working on various non-A-100 Doepfer products like the Dark Matter (Dark Energy expander with Noise, S&H, a second VCO, Multimode-VCF, additional waveforms and maybe some other effects), the Dark Link, and an expansion board for the DIY Synth. 

" ... still on our to-do list. But I can't say in which sequence the planned products will be released."

Note: Please don't call or mail them too often at Doepfer about release-dates or updates of future modules. The Doepfer website is updated very regularly, so you will find all the latest info there...

Using the A-100 for Sound Processing

A-119 External Input /
Envelope Follower

The A-119 External Input / Envelope Follower module allows you to integrate any audio signal (electric guitar, microphone, midi sound module, computer sound card, CD player, tape-recorder ...) into your A-100 system.

Audio inputs of audio-processing A-100 modules (e.g. filter, VCA, phaser, flanger, waveform processor, distortion, wave multiplier, ring modulator, frequency shifter, spring reverb, panning ...) all require line level signals of around 1Vss. , and if the signal source does not have the required level an external pre-amplifier like the A-119 is recommended. 

This module consists of a (pre-)amplifier, an envelope follower and a comparator.

The pre-amp has 2 inputs, one unbalanced (Asymmetric) for line level signals, and a balanced (6.3mm jack /Symmetric) input for inserting low level signals, like microphones or electric guitars.
The module provides two simultaneous audio outputs of the amplified signal.

The envelope follower 'reads' an incoming audio-signal and sends out a proportional voltage as an envelope to its own output.
The brightness of the LED indicates the envelope output level, which is very useful...

The voltage at the output signal can be used to control the filter frequency, loudness or any other voltage controlled parameters such as filter resonance, LFO speed, clipping level, wave multiples, frequency shift, phase shift, delay time and more...

The comparator generates Gate signals out of the incoming signal.

Whenever the audio input exceeds a certain (adjustable) level, a Gate-signal is produced.

This signal can again be used to trigger various other external modules like envelope generators or even voltage controlled switching.

Again, this is a very useful module that i cannot do without anymore because i often use external audio inputs. Most of the times i have a microphone plugged in for vocoder use or for filtering pleasures, but i have used it with my guitar and other audio too.
I do find it a bit strange that it is not included in one of Doepfer's pre-configured basic systems, for me it was a must-have.

One Year www.PatchPierre.net

Wow... time flies.

Today exactly one year ago I started to write this blog, mainly because i could not find a lot of Doepfer user-info on the web. I was looking for a way to share my adventures in analog sound with others, and i looks like i found the right spot.
Sadly i don't have any budget for a give-away (like the wonderful Din Sync blog did) to thank you for visiting/ commenting/ interacting but i do appreciate all your input in this first (and certainly not last) year.

A few statistics:

- A total number of 1000 unique visitors have visited this site so far
- Those visitors came from 77 different countries

- Coincidentally today the site passed the 6000 pageviews too.
- Last months the site has an average of 1000 pageviews per month (but that includes my own too)
- About 30% of the unique viewers are from the USA, The Brits and the Dutch share a second place with around 10% of the total unique viewers each.

Very different are the numbers of my PatchPierre Mobile Nokia application users. Sadly this app doesn't generate an extreme lot of traffic to the actual site, but it did generate around 5% extra visits.

4592 people have downloaded and installed the application so far.

Most of the downloads happened in the counties where Nokia Symbian is a big platform, so most of them happened in India (1067 downloads - 23%), Saudi-Arabia (274 downloads - 6%),Turkey (5.3%),Brazil (4.7%) and Italy (4.3%).

Interesting to see that counties like the USA, Great-Britain and the Netherlands even had less installs than countries like Egypt, Thailand, Indonesia, Russian Federation, Libya, Vietnam and Mexico, to name a few 'odd' ones.*

A lot of them probably used it only once to try it out, but there is a steady group that keeps using the app., around 75 people each month.

So, if you read this blog on your Nokia app, feel free to click through to the real site if you don't want to miss any of the links.
Let me know if you would like to have a Nokia app for your own Blogspot blog... I have two apps in the OVI appstore already, and it is definitely worth it.

There will be a couple of changes to the blog in the next few months. Due to my work i will have less time for the blog again this spring/ summer. I will not post every three days, like i did last 4 months, but i will try to post more than weekly. There are still plenty of modules to write about, and i believe i can't really write about the ones i haven't tried out by myself, but there's still enough stuff to come.
Let me know if you have special requests of topics that you would like to see discussed on the blog. Your input is always welcome, and i hope you will enjoy reading the blog in the next (few) year(s).

My Wordle of one year in Tweets, via http://tweetstats.com

* PatchPierre Mobile stats provided by @wonderhelm

Quotes VII : Herbie Hancock

" Creativity shouldn't be following ratio, it should be the other way around. "

Herbie Hancock - musician, composer, bandleader

Controlling the A-100 via MIDI

In the beginning it was not difficult to pick a Doepfer MIDI-CV interface for your A-100 system.
The A-190 MIDI-CV/SYNC Interface was the only one available and there were not many other options.  (the A-191 MIDI-to-CV Interface / Shepard Generator was way more complex, i will discuss it in a future blogpost).
The A-190 is a powerful module that not only provides a few CV and Gate outputs, but also Portamento, Scale-settings, Pitch-bend, Glide, Clock and Reset signals, has a built-in (software) LFO and very flexible programmability.
Without a proper display it is quite awkward to program, but you'll quickly learn how to read the combinations of burning and flashing LEDs.
I do miss some further (software) development for this module. The arpeggio function, mentioned on the front-plate isn't even implemented (!)

A cheaper option that you can buy nowadays is the  A-190-2 Midi CV/Gate interface, which is based on the Doepfer MCV4. Only some minor changes were made for a better adaption to the A-100 system, e.g. five 3.5 mm sockets and zero-symmetrical CV for pitch bend, to be able to adjust the pitch bend range e.g. in combination with the precision CV adder A-185-2 and the glide function.
The module has no MIDI Thru and MIDI clock and reset functions though.

The new A-190-3 USB/MIDI-to-CV/Gate Interface that is in production stage has almost the same possibilities, but will be a modular version of Doepfer's upcoming Dark Link Module. This one will support USB and the release date for it is set for early 2011.
Another advantage of these two cheaper modules is that they don't need the additional +5V adapter. 

If you are looking for a polyphonic MIDI-CV contoller you will probably have to wait a while. Doepfer is busy working on the A-190-5, but it will be completely redesigned this year. A final version will  probably contain an LC display (similar to the A-187-1), some control buttons, a USB interface and higher resolution DACs with higher voltage range (probably 12 bit and 0...+10V). It will be a four voice polyphonic Midi to CV/Gate interface with 12 CV and 4 Gate outputs and different modes (e.g. unisono, four-fold monophonic, different four voice polyphonic modes.)

Tip: The monophonic MIDI-CV converters can write and read to the A-100 Busboard, more info on this HERE

Booktip VII - Keyfax Omnibus Edition by Julian Colbeck

The Keyfax Omnibus Edition, written in 1996 by Julian Colbeck, is a pretty interesting 192-page book about synths and synthesizer history. It is the sixth volume of a series by the author, his first one appeared in 1985 although he already writes about synthesizers since 1976.

The book is divided into 2 main parts, The Hot 100 and the Product Directory.
The first and largest part of the book delves into the 100 most important synthesizers in history, alphabetically ordered by manufacturers name. Together with the company profiles this book gives a nice overview on the global history of synthesizers. I like the style that it is written in, very informative...

The second part, The Product Directory exists out of an extensive list of almost every synthesizer on the planet. The directory also provides production data like production year, release-prices, the instrument's value in 1996, and often a short extra description. Very useful if you are looking into buying a second-hand ( pre-1996 ) synthesizer.

The book reads like a synthesizer history book. It is a nice resource for anyone interested in older synths and synth history. PatchPierre rates it at 8 out of 10 stars

More PatchPierre Booktips

Published by Mixbooks,
later editions published by Hal Leonard Corporation
ISBN: 0-1918371-08-2

Filters II : A-121 VCF2 Multimode Filter

The first Doepfer filter that i ever bought was the A-121 Multimode Filter. It is a 12 dB/Octave filter, and has multiple simultaneous outputs available; a Low-Pass, Band-Pass, High-Pass and Notch (or Band Reject).
It also has 4 CV inputs, 2 for adjusting the cutoff frequency and 2 for resonance.

This is still one of my favorite filter modules, the multiple outputs are very useful, and i  like all the CV inputs. It just gives you so much more control over the filter, and that's what i like most in a module; maximum control.

Although it is 'only' a 12 dB filter it sounds very nice, from very smooth and warm up to quite rough, especially with the resonance turned up ( ...up to self-oscillation ).
Most of the times i patch an A-174-2 Wheels CV into FCV1, and a simple envelope CV to the (adjustable) FCV2. Works fine in most situations.
With some analog or digital noise added to QCV2 to give it a touch of unpredictable resonance you will quickly get a convincing fat bassline.

Together with an A-138 B (exp) Mixer you can easily make some pretty impressive stacked bass-sounds, all with just a single filter-module.

Find A-121 sound examples at Andreas Krebs Blog : HERE

As the special circuit CEM3320 used in this module is no longer available the module is discontinued. I believe there are still a few available, but they don't make new ones anymore. Doepfer advices modules like the A-106-6 ( with eight simultaneous outputs! ) or A-107 Multi-Type Morphing Filter as a replacement.

SiteTip IV : MIT OpenCourseware Music and Technology: Contemporary History and Aesthetics

A great resource for beginners and all other synthesizer-enthusiasts is the OpenCourseWare site from the Massachusetts Institute of Technology (MIT)

This course, as given by professor Christopher Ariza in the fall of 1997 is highly informative and perhaps a must-read to all of you new to analog sound or music in general.

'This course is an investigation into the history and aesthetics of music and technology as deployed in experimental and popular musics from the 19th century to the present. Through original research, creative hands-on projects, readings, and lectures, the following topics will be explored. The history of radio, audio recording, and the recording studio, as well as the development of musique concrète and early electronic instruments. The creation and extension of musical interfaces by composers such as Harry Partch, John Cage, Conlon Nancarrow, and others. The exploration of electromagnetic technologies in pickups, and the development of dub, hip-hop, and turntablism. The history and application of the analog synthesizer, from the Moog modular to the Roland TR-808. The history of computer music, including music synthesis and representation languages. Contemporary practices in circuit bending, live electronics, and electro-acoustic music, as well as issues in copyright and intellectual property, will also be examined'

Surfing through these pages you will find a lot of interesting information on (analog) sound, music history and much more, accompanied by many links to other interesting reads and audio-examples.

Video: Lecture 13 | MIT 21M.380 Music and Technology (Contemporary History and Aesthetics)


Preview Lecture 13 / Modular synthesizers
See the complete course HERE

Check the massive PDF (37 Mb / right-click and save as) for the complete set of notes and all other information on this course and enjoy!

Licence info:
Ariza, Christopher. 21M.380 Music and Technology (Contemporary History and Aesthetics), Fall 2009. (Massachusetts Institute of Technology: MIT OpenCourseWare), http://ocw.mit.edu (Accessed 16 Oct, 2011). License: Creative Commons BY-NC-SA

CD-Tip IV : Clara Rockmore - The Art of the Theremin (1977)

Okay... Either you love the sound of the Theremin, or you don't. If you count yourself to the last category, feel free to skip this post and return to this blog in 3 or 4 days.

Yesterday was what would have been theremin virtuosa and electronic music pioneer, Clara Rockmore's 100th Birthday.
Clara Rockmore ( born as Clara Reisenberg ) studied violin in Leningrad, Russia, but she had to stop her career because of bone-problems due to malnutrition in her youth.
After she moved to the USA she started to work with Léon Theremin, who had recently invented the Theremin, and very quickly she mastered the instrument and became a virtuoso Theremin player.

In all the years performing with USA's finest orchestras and touring she developed a distinguished technique for playing the instrument and she proved that the Theremin really was a serious instrument, and not just an instrument to make 'eerie' sound effects for scary movies.

Although she also did these sound effects on commission, her true love was for the real classical compositions.

This 12-track CD has special arrangements of great classic composers like Saint-Saens, Rachmaninoff, Tchaikovsky, Ravel, Stravinsky and a few others.

Rockmore plays the Theremin beautifully, accompanied by her sister Nadia Reisenberg on piano. Pure and simple. If you are into classical music you will probably appreciate these wonderful recordings.

I have to admit that the tracks do sound a bit sad or moody, but that might just be the power of Clara's playing-style. With this recording and performances she definitely proved that you can really touch someone's soul with this instrument, and that is a great accomplishment with such a difficult to play instrument.

Video: Clara Rockmore - The Swan from Saint Saëns


CD catalog nr: Delos DE1014

Wikipedia: http://en.wikipedia.org/wiki/The_Art_of_the_Theremin

A few more recordings that were made during these sessions later appeared on the 'Lost Theremin Album' (1989), together with other old recordings.

Also worth watching: Theremin, an Electronic Odyssey, a 1997 documentary about Léon Theremin, his instrument and life, including various interviews and performances by Clara Rockmore.
Trialer: HERE

New PatchPierre Mobile App Advertising Templates

Nice...
Nokia / OVI-publishing recently provided me with new advertising-templates for my PatchPierre Mobile Nokia-app. Very kind of them, this looks much better as the old banners IMO.

If you have a Nokia mobile phone, you can still find the app HERE.

The ultimate way to watch PatchPierre's content on your Nokia device. The app enables easy browsing through the posts, feedback and twitter-feed and also links to the original articles and my NetPierreTV YouTube Channel

Works on all Symbian and selected S40 devices.

PS. if you are an Android, IOS, WM7 or Blackberry developer and you have a little bit of spare time... feel free to contact me. It would be nice to have this app available on multiple platforms. 

Users' Favorite Modules

A recent Poll at the Doepfer Yahoo Usergroup, in the beginning of this year gave a nice insight of what modules are the users' favorites. The (informal) poll resulted in a lot of nice top-5 lists, with a great diversity in modules.
I took some time to count the votes that i could find and made this overall -list. /*the differences between the top-three most-mentioned modules were minimal;

The A-149 Quantized/Stored Random Voltages module(s) were definitely the most popular ones.
These modules, based on Buchla's 'Sound of Uncertaincy' Model nrs. 265/266, process random or stored random voltages to contol your other modules. Very interesting modules, that are high on my personal wishlist as well.

Three modules ended in second place;
The A-101-2 Low Pass Gate, The A-155 Analog Trigger Sequencer / A-154 Sequencer controller combination and the A-156 Dual Quantizer
Third place was for the A-160 Clock Divider/ A-161 Clock Sequencer -combination, the A-151 Sequential Switch, the A-137 Wave Multiplier and the A-198 Ribbon Controller ( R2M included)

I was not really surprised by the list, a lot of them are high in my personal favorites list too. Not sure about the Vactrol LPG module though... i prefer other filters, like the A-121 Multimode Filter and the A-127 Triple Resonance Filter, simply because of their multiple outputs and extended control possibilities... and the A-124 WASP Filter because of its unique sound.

The Ribbon Controller (A-198) is also high on my list, and i also love other 'alternative' controllers like the A-198 Theremin Controller and the A-174 Joystick and A-174-2 Wheels modules.
These last two controller modules were so under-rated in the poll IMO,but sooo useful in live-situations.
My personal number one module is, without a doubt, the A-156 Dual Quantizer Module, but you have probably noticed that already by my earlier posts about this module and it's recent modification.

Feel free to leave your personal list with favorite modules in the feedback section...

Are you curious about what else is going in the Doepfer Yahoo Usergroup?

Click to join Doepfer_a100
Signing up is easy... and free!

Quotes VI : Brian Eno

" As soon as I hear a sound, it always suggests a mood to me."

Brian Eno / Producer, musician, songwriter, artist

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

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 http://synovatron.blogspot.com

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 DatasheetCatalog.com

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.

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

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.

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...

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.

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...

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.

Modifications V : Replacing more LEDs

I am not sure if i should bother you all with every LED i replace, but my first try went so well that i am happy to share my latest update too.

This time i very bravely went for two (2!) LEDs at once. The module i picked for this was the A-166 Dual Logic Module. I thought the 2 inverted trigger output LEDs at the bottom of the front-plate were perfect for this. I don't use these a lot, so the lower 2 LEDs are almost always burning, what also gives a nice effect in the dark.

To reach the soldering-points of the 2 LEDs i had to remove one of the modules boards on the backside.
This was was easy as each board is only fixed with its own 8 sockets. After that i removed the flat connector between the two boards and that created enough access to do my work.

De-soldering the old LEDs was a piece of cake, and the new ones fitted quite easy too.
See my earlier LED replacement post HERE for (safety) remarks, warnings and additional info.

SiteTip III : Tim Stinchcombe's A-100/Modular Webpage

Another useful resource for A-100 and other DIY-projects is Tim Stinchcomb's personal A-100/Modular webpage.

Very interesting for starting DIY-ers, this site is a very interesting read. Don't let the design of the pages mislead you ;)

Most of the projects and instructions on this site can be found via the Doepfer Yahoo Usergroup, but this is a neat collection of some of the A-100 modifications that are not too difficult.

You can also find some Plan B modification instructions on this site, together with other nice DIY-projects like for example this cool stereo LED VU-meter built in a blind-panel to fit a Eurorack system.

Great site... very inspiring.

To Patch... or Not to Patch

'patch'  -  [ pach ] :

verb: To connect together, as the inputs and outputs of various modules, generally with patch-cords.

noun: The configuration of hookups and settings that result from the process of patching, and, by extension, the sound that such a configuration creates.

from: Vintage Synthesizers by Mark Vail

- Related forms:

patch·a·ble, adjective
patcher, noun
patchless, adjective
un·patched, adjective
well-patched, adjective

from: dictionary.com

more on Wikipedia

Modifications IV : Replacing LEDs

 Instead of going the easy route by ordering A-100 modules with blue LEDs, i just had to try to do this by myself. Lately you can pre-order modules with blue LEDs installed for a 2 Euro fee per assembled LED, but i don't believe that was possible when i bought my first modules.

It wasn't a very difficult job, perhaps more difficult was choosing which LED i wanted to replace. As always, i try to keep the look of the system as logic as possible, other examples are the colored switches and colored patch-cables.
( also see Color-Coding )
Plus, for my first replacement i wanted to find an LED that was a easily accessible. I found out that the Doepfer boards are so full that many of the LED are in tight spots on the boards.

I'm glad that i had finally found one; the overload LED from my A-119 External Input / Envelope Follower.
Removing the old LED was easy. I bent it out of it's front-plate hole and heated the soldering-points one by one while pulling the LED out softly.
After that i took the new blue LED, bent the 90 degrees angle the same way as the old one and pushed it gently into the A-100's board again. The solder that was left from the old LED was enough to tightly fix the new one.

A few notes:
- You can not use any LED, only use the same ones that Doepfer provides. Always check documentation for more info.
- Due to technical reasons not every red LED can be replaced by a blue one. ( like the Vactrol modules ) Check each module's webpage before you start.
- Don't forget to check the polarity of the LED's ( + / - )
- Blue LED's are actually transparent/white when they are not lit.

Quick Tip IV : Ribbon Cable

A small personal advice for owners of an A-198 Ribbon Controller or R2M manual controller;

Please unplug the USB-cable when you are not using the instrument.
The weight of the cable has more then once broken the USB-connector on my Ribbon Controller.

Or try to keep the controller and cable on a flat surface...

...also see THIS post.

Blind Panels II

Beside for safety uses, as mentioned in one of my earlier posts, the blind-panels that Doepfer sells are also perfectly usable for all types of DIY-projects.
The 'standard' panels of 4,8,42 and 84 HP can be used for all types of original self-made modules or expanders. Sadly they don't have other sizes, but wouldn't it be nice if they had a 16HP and perhaps a 24HP to 'fill in the gaps'.

Drilling the metal plates is quite easy ( if you use the right tools ), and the panels come with pre-drilled mounting-holes.
If you don't like drilling, you can also order some pre-manufactured panels from the Doepfer A-100 specials list;


They still have many punched A-100 standard front panels of 4HP width, punched for 8 sockets, identical to A-180 front panel but without printing, very useful  for DIY or A-101-9 expansion  applications. You can save yourself some money by making your own A-180 multiple for almost half the price. (sockets can also be ordered at Doepfer )

Punched A-100 standard front panels of 8HP width are still available too. Punched for 5 potentiometers and 5 sockets (same as A-102, A-103, A-105, A-120, A-122, A-123, A-124, A-130, A-131, A-138), without silk screen printing.
They even  fit the Synovatron DIY1 and DIY2 kits. (*confirmed / ,but see feedback for remarks and more info)
Update March 3 2011: Synovatron now sells his own generic front panels for his DIY kits.

Doepfer also still has a few 14 HP front panels punched for 2 wheels and 4 sockets ( like A-174-2 ), without printing, that might useful e.g. for a DIY wheel module. Order it with two modulation wheels and you even get the front-plate for free...

Quotes IV : Wendy Carlos

"A nice blend of prediction and surprise seem to be at the heart of the best art."

Wendy Carlos

http://wendycarlos.com/

A-178 Theremin Control Voltage Source

The Theremin, invented in the late 1920's by Léon Theremin was one of the earliest electronic instruments.
The instrument is known for it's distinctive ( spooky ) sound, but most of all for it's playing method; Instead of playing it with a keyboard, the Theremin has antennas that sense the movement of the players hand, without touching the instrument.
Best known for playing the Theremin is Clara Rockmore, one of Theremins finest students.

Most theremins use two antennas, usually one for pitch and one for volume, so with two Doepfer A-178 Theremin Voltage Source modules, an oscillator (VCO) and an amplifier (VCA) module, it is quite easy to re-create the sound of a 'real' Theremin. You can even easily extend that sound by patching in filters or other modules.

And again, that is what makes the A-100 modular so versatile. 

Instead of just recreating the original Theremin you can use the module as a control voltage source for other modules. 

The voltages can be used for controlling any voltage controlled parameter of the A-100, e.g. pitch or pulsewidth (VCO A-110/111), loudness (VCA A-130/131/132), panning (A-134), filter frequency or resonance from all of the filter modules, phasing (A-125), frequency shift (A-126), resonance peaks (A-127), envelope parameters (A-141/142), and tempo (A-147), to name just a few ;-)

The Gate-output with adjustable threshold (not available on the original Theremin) is a nice extra output. I often use this for (re-) triggering notes or filter effects, but it can also be used for starting sequences (A-155) or for reset or switching functions (A-152).

Doepfer recommends if two or more A-178 are used the distance between the modules/antennas should be at least 30 cm to avoid interference.

Booktip V - The A-Z of Analogue Synthesizers by Peter Forrest

This 'Encyclopaedia of all the great analogue synthesizers and keyboards' is written by Peter Forrest and is probably one of the most detailed analog synthesizers-catalogs out there.

The books list all analog synthesizers that were ever produced, and is spread across 2 parts with a total of 600 pages, filled with useful info about manufacturers, statistics and lots of pictures in black and white.
Both books also have a 16-page full-color-section, stuffed with cool pictures.

The first edition of Part One (A-M) was published in 1994, two years before Part Two (N-Z) arrived. The Revised version of Part One was published in 1998.
Although the layout of the books and some b/w pictures may look a bit cheap the books are highly informative if you are interested in analogue synthesizer history.

ISBN Part One A-M revised 0 9524377 2 4
ISBN Part Two N-Z              0 9524377 1 6
Susurreal Publishing: http://www.vemia.co.uk/susurreal/