Analog User Modifications:

Sequential Pro-One

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Do It Yourself Special:
FREE plans to add MIDI capability to the Sequential Pro-One 
with the Synhouse MIDIJACK!

The following plans describe a method of adding MIDI capability to the Sequential Pro-One analog synthesizer with the Synhouse MIDIJACK.  There is a empty place on the Pro-One jackpanel that is perfect for the placement of the MIDI DIN jack.  The micro size and black color of the MIDI button are such a perfect match for the Pro-One that it makes it look as if it came from the factory with the MIDI interface.  You can do this yourself if you have a little experience with electronic repair and the soldering of wires and cutting traces on circuit boards.  If not,  these plans may assist a professional repair shop installing the MIDIJACK for you.  Some drilling is required to do the cleanest possible installation,  unless the user prefers to mount the DIN jack to the plastic front panel of the instrument.  There is plenty of space on the Pro-One to mount the MIDIJACK with the provided hardware.  This modification extracts the local analog keyboard and CV/gate input signals from the instrument and reroutes them through the computer-controlled analog switching matrix of the MIDIJACK and inserts the users' choice of local analog keyboard,  external CV/gate jack control,  or MIDI.  The particular installation on which this document is based was on Sequential Pro-One serial #1250,  other revisions may be different.  It is best to download these notes and photos and print them out on paper to look at while working on the instrument and make notes and check off the steps as you go.  As with any project,  it is best to completely read and understand each step of the instructions before starting.  All repairs and modifications made to your instruments will be done at your own risk and Synhouse Multimedia Corporation assumes no liability for personal injury caused or damage to equipment or loss of use caused directly or indirectly by the use of these plans.  If in doubt,  don't do it!


1)  Be sure to have the correct tools and supplies for for the job.  If you do not have them,  get them.  You will need a regular size Phillips screwdriver,  a smaller size Phillips screwdriver,  needlenose pliers,  wire cutters or other flush cut nippers,  a hobby knife such as an X-Acto,  scissors,  a soldering iron,  solder,  electrical insulating tape,  and a black Sharpie permanent ink marking pen.  You will need a small length of insulated wire to use as a jumper wire. Any lightweight wire such as the type commonly used for wire-wrapping will do.  If you use an electric drill to make the holes for the MIDIJACK circuit board, you will need a 1/8" drill bit for the 6-32 screws used to mount it. If you intend to mount the DIN jack on the back panel with the rest of the inputs (highly recommended),  you will need to use a chassis punch (a small hand tool that safely cuts a clean hole in a metal panel) to make the hole for the DIN jack,  and an electric drill with a 3/32" or similar size drill bit to drill holes for the 4-40 hardware used to mount the DIN jack,  and also a 1/4" or 5/16" drill bit to make a pilot hole to start the chassis punch.  The correct size for mounting a MIDI DIN jack is 14.5 mm metric or 5/8" SAE (.62"/15.9 mm) in American sizes.  A chassis punch may be purchased from any good tool or hardware store.  If it is more convenient,  a punch may be mail ordered via internet or telephone from Mouser Electronics at or (800) 346-6873.  The Mouser part number is 586-3803 for the name-brand Greenlee 730-5/8 (about $30).  The cheaper house brand part number is 380-0145 (less than $20).  The service from Mouser is unpredictable and the house brand ordered by Synhouse for the test installations took three months to be delivered,  while the Greenlee part was delivered in one week.  Mouser refused to give even a small discount to customers of Synhouse,  so no recommendation is deserved or being made here,  and any other source you know of to buy this type of tool is highly recommended and certainly a better place to buy from for all of your needs now and in the future.  You will also need an 11 mm wrench (for Greenlee) or 1/2" wrench (for the Mouser house brand punch) or adjustable wrench to turn the chassis punch while cutting the hole.  If you choose to mount the DIN jack in the soft plastic portion of the Pro-One chassis,  the X-Acto knife will carve out the hole quite easily,  and will also make the holes for the screws as well,  so no chassis punch,  electric drill,  or drill bits are needed for this alternate quick mounting method.

2)  Fully test the Sequential Pro-One to be converted to MIDI.  Be sure that all functions such as the envelope generators work and that the instrument plays in tune while playing along with a known well-tuned instrument such as a newer digital synthesizer or sampler keyboard.  If it doesn't work properly without MIDI,  it certainly won't work with it.

3)  The installation of the MIDIJACK in a Sequential Pro-One is slightly more complicated than it is with most other American synthesizers because the installer must remove the Pro-One circuit board and cut three copper traces to isolate and access the correct analog I/O signals.  Many older American synthesizers have panel-mounted CV/gate jacks with solder terminals and the MIDIJACK wires can simply be soldered right at the inside of the panel and the whole MIDI conversion job can be done in 20 minutes.  The Sequential Pro-One has jacks soldered directly into the PC board and the safest way to access the signals without compromising the strength of the factory solder joints is to leave them just as they are and cut a tiny notch in the copper circuit trace a short distance away from the jack itself.

4)  Extreme caution should be taken while working on the Sequential Pro-One.  The unit should be unplugged while open and even then,  the power supply may pose some electric shock hazard due to residual voltage in the power supply.

5)  Remove the three flathead screws from the front edge of the instrument beneath the keyboard and the four flathead screws that hold the right and left wood end panels in place.

6)  Open the case and turn the synthesizer upside down and shake out any dust and debris that may have accumulated inside the instrument over the years.

7)  Remove the knobs.

8)  Unplug the three connectors going to the keyboard,  power supply,  and modulation/pitch wheels.  It is a good idea to make a mark with a black Sharpie permanent ink marking pen anywhere across the joint of a mating connectors before disconnecting them.  The unique mark will allow future reconnection in a way that will visibly show whether or not it is the correct connector on the correct mating header with the correct polarity.

9)  There are 9 flathead screws holding the upper main circuit board in place.  Remove the flathead screws holding the circuit board in place and remove the board.

10)  Determine the place where the MIDIJACK circuit board will be mounted and test fit the board into its' correct place inside the case.  A good place to mount the MIDIJACK board is on the panel near the performance controls.  Use the paper drilling template provided with the MIDIJACK Installation Manual to mark the correct mounting holes on the front panel with a pencil,  marker,  or needle by taping it in place and digging right through it with a knife.  Do not use a drill.  The panel of the Pro-One is made of plastic and a drill,  even on its' slowest speed,  will build up friction,  generate heat,  and burn the plastic permanently.  Use a standard X-Acto knife blade with the sharp point and twist it in place until it starts to dig a little hole.  When it gets close to reaching the other side,  you can look inside and see the tip coming through and dig back from the inside as well.  It would be best to do most of the digging from inside the panel to avoid chipping the outer panel surface.  A perfectly round hole can be shaped using this technique.  The photo called Pro-One pic 1 shows the paper template in place and Pro-One pic 2 shows the perfect panel holes after cutting.

11)  Temporarily mount the MIDIJACK board in place without fully tightening the screws and try to get the perfect size holes by twisting the X-Acto knife but do not make them too big.  The switch should be fitted so well in the panel that the switch stem will not wiggle at all once in place.  It should not have any free play but also should not be so tight that it binds.  When the switch is pressed,  it should have a definitive "click" and bounce back like the button on a new VCR.  You will never regret spending too much time on this and good attention to detail will make the perfect MIDIJACK installation.  The hole in the panel that is over the MIDIJACK scale adjust trimpot should be enlarged so a Synhouse Pocket Screwdriver can fit through the panel for periodic adjustment.  The screws that secure the MIDIJACK board in place should be tightened very carefully.  Do not overtighten the screws.  Photo Pro-One pic 3 shows the MIDIJACK board mounted in place near the modulation/pitch wheels.  Such an installation will be nearly invisible,  yet put the MIDI function button at the players' fingertips.  For the serious Analog User and synthesizer collector,  an ultra-clean installation pays off.  The MIDIJACK board should be removed from the panel until final reassembly.
12)  Determine the place that the MIDI input DIN jack will be mounted.  The perfect place is on the rear jackpanel in the blank spot between the CV OUT and GATE/CLK IN jacks.  The way to make this look like original Sequential factory equipment is to mount the DIN jack inside the metal panel after marking the bare metal edges of the hole with a black Sharpie permanent ink marking pen to match the black finish of the original metal chassis.  Use the paper template to mark the correct spots to drill and cut as shown in Pro-One pic 4.  It is advisable to use a chassis punch to make the hole for the DIN jack.  Remember that the DIN jack is to be mounted with the smaller 4-40 hardware size rather than the larger 6-32 size that secures the main board.  Drill two holes for the screws then drill a slightly larger hole in the center to act as a pilot hole for the chassis punch.  Use the chassis punch to cut the hole and be sure that the wrench is turning the tool from inside the Pro-One,  not outside,  so the cutting edge is coming from the outside.  This will ensure that the outer edge is perfectly smooth as shown in Pro-One pic 5. The MIDIJACK hardware packet contains both long and short 4-40 screws for the DIN jack.  Use the two long ones for installation on a thick aluminum panel such as the Pro-One.  When all three holes are perfect,  put the DIN jack in place inside the chassis and secure with the two screws from the outside,  and the four split washers and two 4-40 nuts on the inside against the back of the DIN jack and tighten with a small Phillips screwdriver from the outside and the needlenose pliers from the inside.  These should be very tight as they are going onto the metal surface of the DIN jack.  If done cleanly and correctly,  the Pro-One will look like it had MIDI when it came from the factory.  The DIN jack should be temporarily removed from the panel until final reassembly.
13)  The black and red wires must be soldered in place to get the ground and power for the MIDIJACK.  See the photo called Pro-One pic 6 which shows the best place to obtain the proper ground,  at the left end of resistor R-086 on the far left of the circuit board between the OSC B AMOUNT and LFO AMOUNT pots in the MODULATION section.  The #1 black wire should be soldered to this point.  For power,  the #2 red wire should be connected to the +15v supply by soldering to the front end of R-023,  as shown in the photo Pro-One pic 7.  This resistor is located just to the left of the slide switch in the MODULATION section marked FILTER WH/OFF/DIR.  Unfortunately,  the silkscreen of the circuit board is confusing,  calling all jacks J-048 and has all resistor component markings hidden under the components themselves,  so be extra careful to make the right connections.
14)  The CV connections must be made next.  The PCB will require rework and extra connections to make the MIDIJACK work.  Placing the Pro-One circuit board on a suitable work surface,  locate the proper cutting and soldering points.  Three copper circuit board traces will be cut and four more MIDIJACK wires will be soldered to the top side of this board.  The terminal on the CV IN jack that connects to the tip of an inserted plug must be isolated by cutting the two traces that connect to it.  There is one trace on the top of the board going to the left which should be cut with an X-Acto knife as shown in Pro-One pic 8.  Carefully cut the traces with an X-Acto knife by digging a nice, even groove to break the signal.  Make sure that there are no foil pieces left hanging around to cause a short circuit later on.  There is one more trace coming from the CV IN jack on the bottom of the board which should be cut as shown in Pro-One pic 9.  The bottom of the board is the side where the jacks are mounted.  The terminal connecting to the tip of the plug is the one of the three terminals which is nearest the tip.  When referring to the photos,  keep in mind that the model photographed was a prerelease model MIDIJACK used for beta-testing and made with plain black wires instead of the easy color-coded wiring harness supplied with the MIDIJACK which is in production today.  The two traces that were cut away from the tip terminal must now be reconnected to each other (but not to the terminal).  Use a piece of thin insulated wire such as the type used for wire-wrapping and make a jumper to connect the two points.  An 8" piece of wire is the perfect length.  One end of this wire should go to the trace on the bottom of the board,  and a good place to add it is on a feed-though solder spot on the trace,  a place where the signal goes through the board to the top side.  It can be connected by adding more new solder to the spot the heating and pushing the new wire into the hole as shown in Pro-One pic 10.  The other end of the new jumper wire goes to the rear end of R-110,  a resistor just to the left of the OSCILLATOR A FREQUENCY pot shown in Pro-One pic 8.  Solder the MIDIJACK #4 white wire to this same point.  The new jumper cannot be seen in the photo,  but both the jumper and the MIDIJACK #4 white wire connect at this point.
15)  Solder the MIDIJACK #3 blue wire to the newly isolated terminal on the CV IN jack as shown in Pro-One pic 8.

16)  The gate connections must be made next.  The terminal on the GATE/CLK IN jack that connects to the tip of an inserted plug must be isolated by cutting the traces connected to it.  This trace is on the top of the board going to the right of the terminal and should be cut with an X-Acto knife as shown in Pro-One pic 8.

17)  Solder the MIDIJACK #5 yellow wire to the newly isolated terminal on the GATE/CLK IN jack as shown in Pro-One pic 8.

18)  Solder the MIDIJACK #6 green wire to the right end of R-073,  which is the resistor just in front of the slide switch for gate MODE DRONE/OFF,  as shown in photo Pro-One pic 11.  This was the other end of the trace cut to isolated the gate signal and is a convenient and strong connection point.

19)  Photo Pro-One pic 12 shows the Pro-One circuit board with the MIDIJACK board already connected to the proper points.  A look at this will give some idea of what it will look like when done correctly.  The MIDIJACK #7 brown wire is not needed for this installation and should be taped up on the end to avoid electrical shorts. The MIDIJACK #8 violet wire is not needed and should be taped up at this time, unless used for one of the purposes described in the Advanced Installation Manual.

20)  Carefully examine all cuts and connections made to the Pro-One circuit board for possible short circuits before remounting in the upper chassis.

21)  Remount the Pro-One circuit board in the upper chassis with original screws.

22)  If everything looks good and well-routed,  proceed with mounting the MIDIJACK board and DIN jack with hardware provided.

23)  It is probably best not to use the small cable ties to hold the wires in this particular installation.  Instead,  cut short pieces of electrical insulating tape and use them to secure the MIDIJACK wires to the edges of the nearest circuit boards so they will not rattle and break loose inside the case once the instrument is returned to service.

24)  Carefully examine all connections and leads for possible short circuits or obstructions before reassembling chassis.

25)  Plug in the three connectors going to the keyboard,  power supply,  and modulation/pitch wheels,  noting the correct polarity.

26)  Close chassis and secure with seven original screws.

27)  Push knobs back in place.

28)  Test and calibrate using the procedures described in the MIDIJACK Installation Manual.

29)  This installation can be completed in 60-90 minutes.  Extra time spent making a perfect installation is time well spent.

Performance tips for using a MIDIJACK-equipped Sequential Pro-One:  The gate MODE REPEAT/EXT/NORMAL slide switch should be in the REPEAT/EXT position whenever the MIDIJACK is in the MIDI on mode or using CV/gate control.  It should only be switched while in this position,  and switched to NORMAL before selecting MIDI off mode.  The MIDIJACK MIDI button will activate or deactivate MIDI operation.


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