MidiMiniAfy Studio Electronics ATC-1

(with internal selector)


Webpage last edited 09. october 2009.

Best viewed with the somewhat odd Copperplate Gothic Bold font installed ;-)

 

This page is an attempt of tryin' to show how to perform the MIDIMINIAFY modification of a Studio Electronics (from here called SE) ATC-1 synthesizer for the NOVICE. The modification adds a pure sinewave and a discrete moog VCA to the analogue synthesizer. Readers interested in the name MIDIMINIAFY should look up the earlier SE work - search for MIDIMOOG and MIDIMINI. The first is a real minimoog built into a rack chassis, and the MIDIMINI is a part-by-part clone of the Minimoog - with MIDI (Musical Instrument Digital Interface). You will also find a similar VCA in the SE-1X. More on the MIDIMINAFY-modification.

My SE ATC-1 is a Rev. 1.2 with an additional internal printed cirucuit board (PCB) that holds up to four filter PCB's. My synth also have the latest OS (2.3). When I wrote this I had three filters, the Moog-filter, the TB303-filter and the ARP2600-filter.

DISCLAIMER: When performing this modification you are on your own. This page is a description of my own attempt and is not intended as an official manual on how to perform it. You are responsible for the outcome of your own work. Having said that - my ATC-1 works very well. Any suggestions on improvements/corrections are welcome.

If you don't have any experience at all from pratcial electronics work i.e. soldering - I recommend you send your synth to SE. Some of us tho' - particulary those of us located outside US and use our ATC's on a daily basis will have to do this ourselves. You should not choose the KIT out of economical reasons only.

KEEP YOURSELF GROUNDED!!! The ATC-1 is stuffed with IC's - although modern IC's withstand static electricity better than the ones from the stoneage it's a cheap measure to avoid problems. Also - think about what you're wearing and throw the cat out of the house. Cats are walking static electricity bombs. Yeah - and loose that hooded fleece sweater...

 


Tools that might come in handy...

I wholeheartly recommend the magnifyer... when cutting the trace and inspecting your work. I also use it when soldering.

 

New to soldering? Use Google or have a look here:

http://www.kpsec.freeuk.com/solder.htm

 


Opening the ATC-1 is straightforward. Two screws at the top and two screws on each side.

 

A peak inside the ATC-1

The internal filterselector have to come out. But to get to the screws we need to remove the filters first.

Take notice of the orientation - because when I later write about left/right - front/back... it's THIS orientation I'm aiming at.


Take care when removing the filters. Notice the vinyl stand-offs. Do not attempt to remove the stand-off from the filter. It comes off the selector PCB.

Once you've got a filter removed and inspect it you will understand why.

Remove the selector:

The filters can only be put in one way... but other connectors can be misplaced so...

Take a moment now and make sure you got the orientation of the multipin-connectors marked. Personally I always use a marker - so I don't have to worry about forgetting stuff.

 

It's possible to perform the MIDIMINAFY modification without removing the main PCB - but on my board the capacitor C12 was soldered too close to the PCB for me to get to with my cutters... so I decided to pull the whole thing apart. This have another advantage - you don't need to worry much about getting metal dust into your precious synthesizer when drilling the hole for the VCA switch.

If you decide to remove the main PCB for doing this modification I recommend you pull out your digicam and take a picture of the locations of the metal standoffs between the selector and the main PCB. There are also screws securing the main PCB.

IMPORTANT!

If you - as me - don't hack into synths on a regular basis - PLEASE WORK SLOWLY! There's no need to rush things. You can compensate any lack of skills with pouring some syrup into the process. And PLEASE quadruple-check everything you do.

 


The kit

The MIDIMINAFYKIT from Studio Electronics is two small PCB's. One containing the MOOG VCA and one containing the PURE SINEWAVE-OSCILLATOR. The PCB's have thick sticky gooey on the solderside. The VCA PCB is to be placed atop the CV-in/GATE-in and AUDIO-OUT jacks whereas the SINEWAVE PCB goes on to the PCB itself.

I prefer to have the PCB's free to move around when soldering - so stickin' the PCB to their positions was the LAST operation I did. I didn't remove both the protective films underneath the SINEWAVE PCB.. half of it made it stick good enough... - if it's ever to come off again I thought this to be a tad safer.

Both PCB's have leads installed which are ready to be soldered into positions.


Performing the Modification..

OK - then. Let's start turning our ATC-1 into an even better analogue dream-machine.

The most difficult part of the surgery is to hack into the main PCB and lift the negative side of an electrolytic capacitor (C12). So let's start with that.

Electrolytic capacitors look like small batteries and have a + and - that shouldn't be mixed up. The negative side of capacitor C12 have to be lifted from the main PCB. The drawing shows which side - and the capacitor itself have minuses printed on that side.

IF THE (NEGATIVE) LEG OF YOUR C12 IS ACCESIBLE FROM THE COMPONENTSIDE - IGNORE THE FOLLOWING DESOLDERING TIPS.

On my ATC-1 the C12 was soldered too close for me to get into to and cut... not to mention solder on. I decided to desolder it from the PCB. By holding the PCB close to a lamp I was able to find the correct lead. A couple of turns with the vaccuum pump and the soldering iron made it possible to start lifting the negative side. When lifting the capacitor don't use excess force - you don't want to harm the capacitor.

This next picture shows the location of the negative side of C12. (black dot) .. mark it when you're sure you've located it. Notice that the lead is bent on the solderside. After removing the solder I used my pliers to straighten the lead and pushed it gently out using the soldering iron while pulling/bending the capcitior gently on the other side. I wouldn't attempt to pull out all of the capcitors lead - just enough for the cutter to reach in. Make sure you don't overheat the PCB... it's better to work in intervals rather than heating the workarea too long.

NOTE: If you have an accident with the capacitor - fear not. It's a CHEAP part that you can pick up in most well assorted electronic webshops.

 

Lifting the C12 little by little I've got it out far enough for a clean cut that will leave enough of the lead to solder on later. Cut as close to the PCB as possible (which is why you should use cutters made for electronics.)

Next is lifting the left side of resistor R17 - located to the left of IF1 (with the frontpanel facing you). Here I'm adding a wire to solder the R17 and the C12 togehter... where the crocodile clip is located the insulation is removed for soldering the violet lead from the new VCA PCB later. Also notice that the drawing says green/violet. On some issues the color coding is different. On mine the lead is VIOLET.

 

The finsihed joint of C12 and R17 and the VIOLET lead from the VCA-PCB. Also notice the addition of the BLUE lead which now is soldered to the point from where C12 was lifted.


 

Now is a good time to take care of the next preparation of the PCB... cutting a PCB trace close to the IC marked U29 (to be used for the SINE-PCB mount later). A number of tools can be used to perform this - see above, but a miniature sharp screwdriver can also do the job. The cutting is done by scraping into the copper-trace - until it's fully cut - and a little more for safety. Again - work slowly and make sure you're not cutting the trace nearby.

This is miniature work and you will not be able to be 100% sure that the cut is good without the aid of your multimeter. Looking at the drawing - check that there's no connection between the soldering point you isolated and the IC leg.

 

Photo shows WHY you should use a multimeter to check if the trace is properly cut. Red arrows show where to measure.

 


The VCA finished. By comparing the drawing at the bottom of this page and this photo I recon you'll avoid making any mistakes. The blue arrows show the soldering points. Notice the blue frame which show location of the red wire.


 

Next is the SINEWAVE PCB.. Since we've already cut the trace at U29 the rest of the job is easy. This picture also shows a fair location of the sinewave PCB (sorry about the flash...made the photo a tad too bright there...). From top... The black lead goes to the corner right leg of IC U29, the blue wire goes to the point we disconnected by cutting the trace. The rest goes into ready made soldering points. The violet connects to the broad trace, the grey to the trace below, and the white even one trace further down. And that's it!!

 


A HOLE IN THE CHASSIS FOR THE SWITCH...

This is a pretty straightforward job. Just make sure you cover up any electronics properly. You don't want any metal dust into your ATC-1. Use whatever you've got in hand... personally I cannibalised a plastic carrying bag and secured it with some tape. Photo shows switch in place and the blue frame shows the hole. The drawing below indicates which position is the original VCA and which is the Moog-VCA. You may want to mark the back panel... but hey it's not that much to remember is it??


 

JOB FINISHED!

The Main PCB is back in place, as is the filter-selector - and those of you with a sharp eye will also notice the addition of my latest SE purchase - a shiny new ARP2600 clone filter to the right... yummy!!! NOTICE: I recommend that you don't push the filter standoffs into place before smoketesting the unit. If you have to redo something it's easier not having to pull them out of their pretty tight holes one more time. Hopefully you will experience the same as me... no smoke (phew!).


ARTWORK BY THE FABULOUS GREG ST. REGIS...

A few inquistive emails to Greg and the drawing below was what I had at hand when performing the Midiminafy modification. You'll find that everything I've covered above is present in this drawing. I don't know how relevant this is for other versions of the ATC-1 (the ones with external selector and those with the cartridge - but I recon you'll find some usefull information on this page whatever your ATC is... even the ATC-X).

 


Back in the rack and a word on ergonomics...

Here's my ATC-1 back in the rack... I really don't mind that the switch is located on the back - because I will probably use the new VCA for the most. It's perfectly possible to lengthen the leads and put the switch elsewhere, but I have not covered that here. Also notice the Behringer BCR2000... there's a plenthora of cheap MIDI-knobs out there to make your ATC-1 the most knobby synth of them all. Just keep'em within' reach - for instance like this:


 

Tired of scrolling??

Well that's the good ol' way of making webpages.

Hopefully you will now know what it takes to perform the Kit-version of the Midiminiafy modification. It's not a question of IF you should get mod or not.. it's more a question of HOW.

The modification makes the ATC-1 a significantly more mature analogue synthesizer.

SOME MP3 DEMOS... the first one is a mix of standard patches and some made by me (The Taurus-impersonation) without the modification and the second one is exactly the same with the VCA modification turned on. The MIDIMINIAFIED one is slightly louder. So to observe difference in timbre one should adjust the volume somewhat. :

ATC-1 WITHOUT MIDIMINAFY VCA

ATC-1 WITH MIDIMINAFY VCA

Thanks to Studio Electronics and the brothers St. Regis for their assistance and encouragement!