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Build thread for Retroaktiv PG-800 Mini for JX-8P, Super JX
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Build thread for Retroaktiv PG-800 Mini for JX-8P, Super JX
This thread is for people building the Retroaktiv PG-800 Mini controller for Roland JX-8P, Super JX, and MKS-70. The controller does everything that a stock PG-800 did and more. Features include a random patch generator, scratch patch generator, tone copy/paste, manual, and a page 2 function that gives Vecoven 4.x users full hands-on access to all extra Vecoven parameters, plus upper/lower balance, and all aftertouch functions. DIY kits are available for both the desktop unit, and the units that can be installed directly into the synthesizer. To purchase kits, please visit

If you are having any issues with a build, please post in this thread and I will help you. Thanks!
I have gotten some feedback from a few builders, and I want to leave a few notes here.

There is a discrepancy in the schematic, specifically with the values of R60, R61, R62, and R70. The values in the old schematic will work fine, however, those aren't the values I used in the online Mouser parts list. R61 and R62 should both be 1k. R60 should be 470, and R70 should be 390. That means that the +5V will read a little under 5V, and the 2.5 should be around 3.8V.

C42 needs to be 22uF @ 35V. The rest can all be 47uF @ 10V. The footprint for C13 can fit the large 22uFs but I have been using the 47uFs due to the price.

This is a BOM for the basic build using the above values:

Qty Component Value
1 R60 470 ohm
1 R70 390 ohm
1 R61 1K
1 R62 1K
3 C9, C10, C11 0.001 mfd 0603
10 C1-C6,C12, C14, C15, C21 0.1 mfd (C0G)
2 C22, C23 47 mfd @ 10V
1 C24 47 mfd @ 10V
2 R55, R56 10K
2 R41, R59 1K
1 C42 22 mfd @ 35V
4 R53, R54, R57, R58 4.7K
3 C13, C29, C43 47 mfd
3 L1-L3 100 uH 0805 Coil
6 U1-U6 CD4051B MUX
2 U12, U18 LM317 IC
1 U11 6-pin 0.1 headers
2 U9, U10 Switch
1 Q1 MMBT4401 Transistor
1 6-Pin DIN Female 2x3 .1" Breakaway Header

If anyone's unit only allows the parameters on the JX to display 0-97 or 0-98, reduce C11 or simply remove it.

Do not stuff C9

The PCB can also be used to prototype MIDI controllers. There is no code for this, but the circuitry is there for experimentation. Obviously this requires that you write your own code, but the PCB is built to be used for this purpose as well. If anyone wants a PCB for this purpose, a bare board is $25, which includes BOM and schematics. The rest is up to the builder.
I've had some more build reports, and wanted to post them here.

1) When building the DIN connector, the manual erroneously says that pin 5 is the +15 (which should not be connected.) It should say that pin 2 is the one not to connect. The silkscreen on the PCB is correctly labeled. There was just a typo in the manual.

2) Pay attention to chip orientation. IC6 is oriented differently than IC1- IC5. This is indicated on the silkscreen, but it's easy to be careless.

3) A note from a builder: "I used the overlay as a guide to finding pots that weren't quite straight. Just loosely lay the template on top of the pots to find out which ones need 'straightening'."

4) Pin 3 on U11 of the schematic is labeled +15V. It should say +7.5V. The silkscreen on the PCB is correct.

I'll post more build notes here if I receive any more feedback. So far everyone who has built the unit has had success!
Completed the build and installation of the PG-800 mini into my JX-8P over the weekend. Will post a semi-detailed guide with pictures here.
Seeing as I successfully installed the PG-800 Mini in my JX-8P over the weekend, I thought I'd create a quick implementation guide for the 8P, which differs slightly from the Super JX (which is included in Retroaktiv's installation manual). I ordered a bare PCB + Pots from Retroaktiv and assembled the board myself, which was slightly more difficult than installing the board in the 8P. As an overview:

1. Open the 8P - Remove the six small screws on both sides of the 8P, then the back two larger screws on the left-hand bottom (there are many online guides detailing this procedure). The case will open from the front like a suitcase - there are three metal hinges holding the case to the bottom wooden panel.

2. Plan and measure where the PG-800 mini will be installed. On the right-hand side of the large motherboard, there is an empty space with bare metal (just over the power transformer and transistor heat sink). The PG-800 will consume just over 13mm of 'headroom' within this space. Since the 8P has a sloped surface, the clearance over the heat sink and transformer decreases as you move closer to the front of the keyboard. Just at the front of the PG-800 (the edge closest to the keyboard), I measured 15mm of clearance over the front edge of the transformer (when pressing down on the case). Close, but an acceptable amount of clearance to proceed with the installation.

3. Placement prep: Measure the distance to the power switch on the right hand side and replicate that distance on the top of the case to determine where to place the template (which is included with the kit). It's important to leave sufficient space for the right-hand motherboard edge connectors; again, the clearance is close when clearing the power switch, but not uncomfortably so. You should also vertically center the template within the 'raised' portion of the top surface.

4. Drilling prep. After measuring and placing the template (using the magnetic patch guide to hold the template in-place), tape down all four edges of the template to ensure that it stays put while marking hole placement. Using a sharp punch and a mallet, firmly strike the center black dot of all holes on the template: 44 pot holes; 6 mounting screw holes, and two switch holes: 52 holes in all. Remove the template and ensure you marked every hole. I'm not a big fan of removing boards from old synths, so I ended up creating isolation barriers (like surgical draping) over all of the electronics using poly (for the power supply components), and anti-static material (for covering the motherboard), making sure to disconnect and tuck away the two motherboard connectors on the right-hand side of the main board. You can certainly remove all the boards and three hinges to transport the case to a drill press. It's important to not oversize the 6-1/8" board mounting holes, so I circled the holes and indicated the required bit. I also marked the two button holes, as they don't quite require a 1/4" hole - more like 7/32", but 1/4" will work as the template holds the buttons in-place.

5. Drilling. Using metal bits (Cobalt bits seemed to last the longest), pre-drill small (5/64") holes from the top of the case using your drill of choice. I used a cordless hard drill at high speed with a drilling lubricant. You can start the hole by centering the bit on the punch divot, then slowly expand the center hole with light pressure; with your free hand firmly grip the case, and if you 8P is on a table, make sure it doesn't 'walk' off the edge during drilling. At this point, you can add the lubricant and complete the hole. Accuracy is critical for the mounting holes and button holes. Drill the two mounting holes on the left hand side, then use the PG-800 template (the sticker - not the paper one) to ensure all holes are still lined-up. You can use a fine-tip marker to circle the remaining mounting holes and ensure the punch mark remains centered. The steel case is beefy and each hole requires 30 seconds to a minute to drill through. Take a break if you need to - patience and accuracy is important. Once the 52 pilot holes have been drilled, double-check that all the holes are centered using the template. Note any that are off; you can re-center them by drilling another hole using a 1/16" bit (one of my holes was a few millimeters off and I had to re-drill). After confirming that all holes are centred, use the 1/8" bit to expand the mounting holes - one at a time with steady pressure and lubricant, and after each expansion, confirm the placement of the other holes with the template. Next, drill the two button holes using a 7/32" bit, and finally all remaining holes with a 1/4" bit. Make sure your bit is mounted securely - when the bit 'breaks through' the steel it will tend to bind. One trick is to carefully listen for when the bit transitions from 'rattling' within the hole to a very smooth operation and back off on the pressure and increase your grip. I didn't mangle any holes, but many did have a piece of metal on the back that required cleaning.

6. Clean-up and fitment. Using a Dremel tool with a small grinding bit, or a reaming bit, clean up each hole to remove hanging bits of metal. You can carefully pass your finger or a paper towel over each hole to make sure there aren't any snags. At this point, you can 'dry-fit' the PG-800 mini to see what requires adjustment. First, mount each of the 6 standoffs to the board; note that this differs from the installation manual where the standoffs are mounted to the case - either way will work. The standoff goes on the pot side and the mounting screw is fed from the bottom. This ensures that the board fitment does not pass the final placement. Starting from the left or right-hand side of the PG-800, carefully line up each pot with each hole, holding the PG-800 at an angle. You can use a plastic or wooden stick to gently 'guide' pots that are slightly out through each hole. If the PG-800 is really stuck at one point, remove the unit and determine if the hole needs to be adjusted or the pot is misaligned. Both are easy to fix - simply ream out the hole using a Dremel tool or 1/4" bit and clean up any sharp pieces that stick out, or examine the pot to see if it's crooked and requires minor straightening. With patience, the PG-800 will eventually fit through all holes. Turn each pot to ensure smooth operation. You'll likely have 5-6 pots that feel 'tight' at this point you can again either expand the hole or adjust the pot. Using a sharp marker, create a mark beside any pots that feel tight and remove the PG-800. Ream out the holes and repeat the process until the pots feel smooth. At this point, you should temporarily mount the board from the top through the standoffs to ensure clean operation. You can also use your soldering iron to adjust the pots while the board is mounted. Determine if the pot requires adjustment left or right, and use the iron to flow the solder for the center and left (or right) legs of the pots, while applying gentle pressure to the pot. All pots should move freely at this point, and the buttons should pass through the holes and mount in the square switch receptacles. Remove the mounting screws and PG-800 mini and set aside. Once your pots, switches, and mounting holes are all lined-up, you can use a vacuum and magnet to remove the metal shavings. Never vacuum electronic components with a regular vacuum - the tip of the vacuum generates enough static electricity to damage electronic components. Stick to vacuuming metal, then use a magnet to collect any remaining pieces before removing the plastic shield. Obviously, if you removed the case, you can re-mount it at this point.

7. Soldering the connections. Initially, it appeared that all of the connections to the PG-800 DIN connector could be accessed from the top side of the motherboard, but PIN 6 is 'hidden' within the connection, which required removing the motherboard. Well, technically, I could have soldered to the leg of a capacitor connected to pin 6, but decided against it. Ultimately removing the motherboard is simple. Unscrew the five screws at the bottom of the board and the top four screws, making sure not to drop the grounding brackets. The board will be free at this point; you can lean it back over the keyboard with all other connectors still connected to expose the board side of the PG-800 jack. There are five placed to solder, but be careful - the board is now 'flipped' from left-to-right in relation to the solder points in the Retroaktiv guide. This is because the guide uses the component (top) side view from the Roland service manual, and we are soldering to the board (bottom) side. So left is right and right is left. In the picture below, orange is P1 - Data, red is P4 - ground, yellow is P3 - 7.5V brown is P6 - clock and green is P1 - ready. The solder point of pin 2 (which is unused on the PG-800) is just below the green wire between the yellow and orange wires. At this point, you can re-mount the main board - ensuring the ribbon cable and other wires are safely tucked out of the way. You can add a zip-tie to the ribbon cable, which is a bit long for the 8P, and solder the corresponding ends onto the pads or solder points of the PG-800 mine. I fed the ribbon cable from the back side through the holes and soldered on the top side of the board, but the pads can be used as well - just be sure to use a meter to validate which pad belongs to which connector.

8. Final mounting. Using a cloth soaked with 99% isopropyl alcohol, clean thoroughly on the top surface of the case around the holes, making sure to remove any cutting oil, fingerprints, and marker. The case should quickly dry. Reconnect the side connectors of the main board before mounting the PG-800, as there isn't enough clearance to plug in the connectors when the PG-800 is in-place. Passing the PG-800 through the holes as before (with some careful coaxing), ensure the standoffs are all tight to the case and the pots turn smoothly. Peel the sticker (there's a split point) off the label and carefully lower the decal down onto the top of the case over any pots, ensuring that the pots are all centered before applying firm pressure. Make sure the label sticks from the centre out to avoid bubbles. Rub down the label from the center out with the back of your fingernail to ensure a clean fit, then screw the mounting screws into the standoffs through each of the 6 holes. If you haven't already done so, you can also pass the buttons through the holes from the top-side. If any pots are now tight and they weren't before, they are likely just rubbing against the sticker. I had two that were a big tighter, but after a few minutes of use, they loosened up again.

9. Clearance check. Before closing the case, it's a good idea to ensure that your PG-800 mini clears the heat sink and transformer. The heat sink should not be an issue as there was > 10mm of clearance in my 8P, but the transformer is close. Using a thin layer of silly putty, place the putty over the top of the transformer and close the case. If the pots leave impressions in the silly putty, it would be a good idea to ensure that the top of the transformer is covered to protect the PG-800 mini from shorting out. I ended up trimming the leads of two pots, which gave me about 3mm of clearance, but I also covered the top of the transformer with plastic (as a backup measure). If worse came to worse, and the board doesn't clear the transformer, you could move the transformer towards the back of the keyboard with new holes and mounting bolts.

10. Test. Close the lid and power on the 8P - you should be greeted with your usual countdown and operation, but upon manipulating any of the PG-800 controls, the program number will flash indicating that a parameter has been modified. Pressing the parameter button on the keyboard will allow you to see which parameter is being manipulated and the value in real-time (very cool). All other PG-800 mini operation is covered in the Retroaktiv operation manual. My PG-800 was 'stuck' sending a parameter when I initially mounted it. As it turned out, one of the pots that was 'tight' was sending a constant signal, and when I adjusted the pot for a better fit, the board worked flawlessly.

The PG-800 mini is what I imagine the JX-8P should have been sold with - it was in vogue for synth manufacturers to jump on the digital control bandwagon when the 8P was released, but in the process, they also removed some of the pure joy of sound creation and live performance manipulation that comes with knobs. As with all classic synth mods, I have my reservations, but to me, the PG-800 mini really 'completes' what the 8P should have had in the first place.
There was a bit of confusion regarding the labeling on the schematic vs. the PCB & manual. I have updated the schematic on the website, so the corrected version is available for download.

Here are the corrections. When I first made the prototype units, I was using the +15V from the JX instead of the 7.5V. Everything in the schematic that says +15 should say 7.5V, as indicated on the PCB.
The original schematic also used 5V and 2.5V for the regulator output voltages. That's what is printed on the PCB, but the voltages are actually more like 4.8V (instead of 5V) and 3.8V (instead of 2.5V) when you use the suggested values in the BOM and the schematic.
Nice guide, Amonti!
I've done things slightly different: I scanned the drilling template, mirrored it (use Gimp or whatever), print, and glued to the inside of the jx8p. Punch and drill trough the paper. I removed the front and all the boards.
Only the top row of pots can't be drilled that way due to the angle the back of the front plate makes.
As there are no exact metric equivalents for the drill size, I ended up drilling the pot holes way bigger: they get covered by the label, much easier alignment.
Yes, thanks amonti for the great build guide! I have a JX-8P that will be getting one of these at some point, so it was good to see how you got on.
Is it correct that I can use the $180 bare pcb kit for assembly in my own external chassis?
My understanding is I would order the bare pcb kit and use the "desktop/no midi hardware" mouser BOM.

A second question: for vecoven synths, is there any possibility to daisychain two controllers together, such that one is always in page one while the other is in page two mode?

mrand wrote:
Is it correct that I can use the $180 bare pcb kit for assembly in my own external chassis?
My understanding is I would order the bare pcb kit and use the "desktop/no midi hardware" mouser BOM.

A second question: for vecoven synths, is there any possibility to daisychain two controllers together, such that one is always in page one while the other is in page two mode?


The $180 kit comes with the pots, pcb, panel, uP, mounting hardware, and 5-conductor cable. Since you're talking about making your own panel, you probably aren't going to want to use the panel or pots used on the PG-800M. The pots are PCB mount, not panel mount, so without using the layout configuration of the PCB, these aren't going to be great for any custom panel. What you probably want to do in this case, is just buy a PCB/uP combo from me directly, then use my BOM (internal, no MIDI), but add 44 100k pots, and two momentary push button switches of your own choosing. You'll need to use flying wires to mount your pots to your panel.

As for daisy chaining, that's not a very reliable situation. I've done it with my JX10 (with Vecoven 4.x firmware) and it always results in the machine eventually freezing. If the two controllers ever send messages at the same time, then the JX gets a scrambled message and hangs.

You could use 2 PCBs, and populate the processor in only one. There are 6 free pins on the uP currently. Those could be used as enable pins for the 6 muxes on the 2nd PCB. Then you'd need to connect the MUX ADDR lines (3 total) from board 1 to the MUX ADDR lines on board 2. There are a few other connections like power, analog mux out, and ADC VREF that would need to be daisy chained on the boards. I'd need to make an altered version of firmware omitting PG 2, and scanning 12 muxes instead of 6. (88 parameters instead of 44) That would do the trick. You'd need 2 PCBs and 1 special version of firmware in this case. I can sell you bare PCBs if you want to go that route. PM me here, or email me if you want bare PCBs.
Update: I'll be posting a new version of firmware next week. The new version features a couple of small improvements and additional features.

Pin 6 of the uP can now be used for a Page 2 LED indicator. (Vecoven 4.x firmware users only) The pin is 5V if Page 2 is active, and 0V when not.

I also improved the scanning algorithm. In the 1.0 firmware, a change of + or - 5 was needed in order to make a knob become the "active channel" (The parameter that you want to control). This was done to prevent knobs from sending messages when a finger brushes against them. The new threshold is + or - 2, which feels better. This was done by adding hysteresis to the active channel, which also means now there will never be any jitter when a pot is set on the edge of 2 values. This allows for very fine control.

The 2.0 firmware will be posted some time next week, once I've done more bug testing. To get the 2.0 firmware upgrade, you can download the BIN files from the website, send me your uP to be flashed for the cost of postage, or buy a uP at the cost of the IC + shipping. The IC is $2.

To program the chip yourself, I recommend using something like a USBTiny. You can use AVRDude to easily flash the new firmware. To connect the programmer, your PCB will need breakaway header pins soldered into the ISP jack (to the right of the processor on the top side of the PCB). Hopefully the BIN files will be posted early next week.
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