Future Sound Systems AJAK 2 Bipolar LED Voltage Indicator

Although i am on a very tight budget lately (I still haven't got the funds to fix my mixing desk), I did have a tiny amount left on my PayPal account to treat myself on a new little gadget.

Today I received my package from Future Sound Systems, a small independent musical device manufacturer based in both Gloucestershire and Surrey, England.

FSS builds modular synthesizer components and accessories, predominantly for Eurorack format.

I blogged about their APOW +5Volts module a week ago, you can find it HERE.

Future Sound Systems AJAK2 Voltage Indicator

The AJAK2 is a simple device that you can plug into any mini-jack-socket to check if there is any voltage output (positive and negative)
Basically it is a 3.5mm jack plug connected to bipolar LED, where the Blue LED indicates positive voltage, and the Red LED indicates negative voltage.
It is also available in a Red/Yellow version as AJAK1

It's a fun little thing, especially if you like blinking lights on your Eurorack... like i do :-)

The indicator is (almost?) identical to the LADIK Modular Checker that i blogged about earlier this year, I assume that this one also starts glowing if it registers a signal of approx 2 Volts, but i have no equipment to check this...

Available via www.futuresoundsystems.co.uk

http://www.youtube.com/futuresoundsystems

Bla-Bla Blue LEDs

And again, i have been too busy lately with replacing some red LEDs by blue ones. I believe this was my final batch, but you'll never know...

As i mentioned before on this blog i like those blue LEDs a lot, but some modules weren't available with blue LEDs at the time i bought them.
I'm not considering making my whole A-100 system with blue LEDs, that would be too much, but just a few blue lights make my machine just look sooo cool. (in the dark)

This kind of work also helps me to practice my soldering-skills.
I'm (still) not the best in it, but i am slowly improving... and i do these replacements in less time.

I do not pick my LED-replacements completely at random. Most of my new blue LEDs have a  'deeper' meaning; better see it as a kind of color-coding.
Some of these LEDs need special attention, others sometimes act (slightly) different than the red LEDs next to them, and if there is no direct reason to change a red LED into blue i'll always tend to find one...

Take a look at the new overload LED of my A-126 Voltage Controlled Frequency Shifter ( that is no longer available ) for example. This little LED just screamed for attention every time i used this module.
Earlier i replaced the overload LED of the A-119 External Input, so it seemed logic to replace this one too.

The other LED that i replaced was one of the A-147 Voltage Controlled LFO.
I'm not sure why exactly, but three blinking red lights in a row... Who needs that?
I replaced the middle one, the one that displays the output of the rectangle wave.
It is the only one that does not gradually fade out and in like the other two, it is either on or off, at a CV controlled variable speed...

...I told you I'd find a reason... ;-)

A-147 VCLFO with 1 blue LED

More on replacing LEDs HERE

More Blue LEDs

Okay... I haven't had much time to write and post these last weeks because i'm too busy working this summer, but i'm not completely sitting still.

The new blue LEDs that I ordered arrived, so the next few weeks i will only be replacing some red LEDs by blue ones.
It's not the most exiting modification, but it will make my A-100 system more pretty IMHO.
( Info on replacing LEDs HERE )

I do have time to read during my work, and i'm reading a very interesting (Dutch) book called "Onder Stroom" by Jacqueline Oskamp at the moment.
This book tells the story about the history of electronic music in the Netherlands, so expect a book-review of that in the near future.
( The book is slightly related / overlapping  THIS )

I will be back with some more interesting posts in a few weeks... so please stay tuned!

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

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.

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.