| Legal: I, Lorin Edwin Parker, AM NOT RESPONSIBLE FOR ANY DISASTERS OR MISHAPS THAT ARE INSPIRED BY THIS HOW-TO - INCLUDING THE POSSIBILITY OF INJURY, DEATH OR FRYING YOUR MOOG. This tutorial is a thorough discussion of the techniques I used to make a power supply for a Moog Rogue, but may not apply to your project or your synthesizer. It is intended primarily for educational and demonstration purposes. |
The original Moog Rogue
uses a 24V AC
wall-wart power supply. The 24V AC input is rectified (turned into DC)
and regulated by the following circuit. (schematic from moog service
manual).
Analysis:
Power In - J5 is a 3.5mm jack, like a mono headphone jack. When plugged in, AC electricity from the wall-wart enters the circuit - tip to a switch (marked power sw1) and the sleeve goes directly to the synth's ground. When powered on, the 24V AC goes through the non-grounded lead and gets turned into positive and negative DC by CR8 and CR9. The capacitors C37 and C38 buffer and filter ripple out of the DC power. The 78M12 regulates the power, making it a steady +12V. The 79M12 regulates the negative power supply and creates a steady -12V. The ground, shown in between the positive and negative regulators and capacitors provides the reference point for power regulation.
Approach:
We want to replace the power in jack with an internal transformer that turns 110V AC into the 24V AC the Moog wants to see. We also want to IMPROVE this power supply's quality by adding further filtering to the power supply and providing a three-prong, fully grounded outlet and a fuse to protect the circuitry and ourselves.
Any audio gear only sounds as good as its power supply -- a bad power supply is to blame for almost all cases in which audio gear picks up 60 cycle hum and is often responsible for transient interference and spikes - hiss, crackle, radio interference, etc. Some devices like power amplifiers are more forgiving of ripple and spikes in the power supply, but synths are CERTAINLY not. The Moog Rogue, being a lower priced model, has a few corners cut on the power supply. The Rogue power supply is arguably the weakest part of this synth. We're going to change that...
The filtering and regulation shown in the schematic above is good, it eliminates ripple and filters well. The rectifier is also fine.
We are going to replace the transformer in the AC Wallwart with a Chassis mount power transformer. We are also going to add some additional filtering to the AC line power. A 3 prong earth ground or safety ground, and a fuse to protect the synth, our house wiring and ourselves from electrical accidents or damage.
Here's what my new, modded design looks like:
EMI-RFI AC line filters come in convenient, pre-assembled
packages, often with an IEC connector socket to connect to the mains.
These are easy to find in electronics supply shops and catalogs. I used
a corcom module from Electronic Goldmine.
Calculating Fuse Rating:
The synth requires about 200mA of AC current. Since we're fusing the primary (to protect the transformer as well), there will be a different current draw here than on the other side of the transformer. The calculation for the transformer ratio is V(primary)/V(Secondary). 120V / 24V = 5 --- so, current is 1:5 (primary:secondary). So, 200mA load on the secondary is 200/5 = 40mA on the primary side. Pretty small. So, a .1A fuse should be good. This should blow if more than 500mA is drawn by the load -- which is FAR less than can damage the circuits of the synth.
The Project:
If you really want this internal power supply on your Rogue, but don't have the chops to do it yourself, you can contact me - lparker@calarts.edu. Maybe I'll do it for you...
Parts:
1 24V AC Chassis Mount Transformer that will fit inside the case.
1 Fuse holder
1 .1A fuse
1 IEC Power entry with RFI / EMI filter
1 Power Switch (rated at least 120V AC SPST or DPST) - (or get an IEC Power entry unit with a power switch included in the unit)
Wire
Heat Shrink Tubing
Electrical Tape
Tools:
A Power Drill
Drill Bits (a stepper unibit is HIGHLY recommended)
Screwdriver
Multimeter
For cutting square metal hole - Metal File, Saw (scroll saw or jewelers), or nibbling tool depending on method used (strategies are shown here).
1. Open the Rogue. Unscrew the bottom screws, the two in front on the side panels beside the keyboard and the LOWER screw on the back. Don't unscrew the screws holding the circuit board in place (these are higher up on the back). Now, you can do this mod without removing the circuit board, but I suggest removing it to eliminate the chance that you'll damage it. Also, you can unplug the molex connectors that join the top chassis with the keyboard (Be sure to note which way they go so you don't plug them in backwards when done {I draw a red line on one side of the molex plug and jack. When I reconnect if the two lines don't reconnect I know I oriented them wrong}). It's much easier to work with the synth if the two pieces are separated. Remember, you need to take off all the knobs to remove the circuit board.
Optional - De-solder and remove the old power jack from the circuit board. A good thing for safety, accidentally plugging in the old wall wart and the new supply simultaneously could be VERY bad. I would eliminate the chance by getting rid of the jack. Marvel at how cheap the component is.
2. Place the transformer - It's heavy, so it's a good idea to center it to keep the instrument balanced. Make sure it fits - there is lots of room, but measure first and make sure that the case closes without the transformer touching the circuits above before you drill any holes.
Mark the drill points for the transformer mounting with a sharpie or scribe.
Center tap the points you marked.
Drill the holes (size depends on the transformer, but approx. 1/8" bit ordinary) - be sure to hold the chassis down firmly or clamp it, use tapping fluid or lubricant to cut the sheet metal. (Things like WD-40 or even Olive oil will lubricate a little if you don't have tapping fluid, but don't cut it dry).
Line up the transformer and place 4 small bolts through from the outside of the case. Tighten a nut down to secure the transformer to the case. (4-40 bolts and nuts were used here, but bigger holes might use 6-32 or larger).
3. Place the IEC entry, the fuse holder and the new AC switch (if applicable).
Mark the square hole you need to cut for the IEC plug entry unit. Use a sharpie or metal scribe. Make sure it's within reach of the transformer's primary leads (usually black).
4. Drill or punch the hole (or holes) for the fuse holder and the AC switch. I chose to use a chassis mounted easy access fuse holder. I drilled a 1/4" hole and used a 9/16" Greenlee punch to make a clean hole (a stepper bit will work well too - I just happen to have the punch).
Punching the hole for the fuse holder
with a 9/16" Greenlee Chassis punch. (Don't forget to lubricate).
5. Wire it -
Moog to transformer -- Look at the picture below and then use a multimeter to find the exact points! Circuit boards vary. This is why I don't have a close-up.
1. Find the point where the TIP of the wall wart connector connected to. Follow the trace to the switch - it should lead to the center pole of the power switch. Solder the wire into the hole / pad left when you removed the wallwart jack or the switch's pad. This is the positive supply.
2. The green wires on the smaller circuit board are all ground. Solder the a negative wire lead to one of these points.
3. Check it! Using the continuity checker with your multimeter make sure the negative lead you added is connected to ground. Check it in a few places - with one lead connected to the loose end of the negative wire you attached: check that it is has connection / continuity with the sleeve of the audio out jack, other green wires on smaller board, the screws on the small board that connect to the heat sinks on the voltage regulators (all these are connected to ground). Next, make sure that there is no connection to the positive wire you just connected.
4. Find the white/red striped wire from the main board to the smaller board. With the rogue's power switch off, there should be no connection to the new positive wire. With the switch on, there should be continuity.
Finally, use the schematic and your eyes as a guide. Make sure there aren't solder bridges on the new connections.
Wire the transformer, IEC plug and fuse according to my schematic. Make sure that the wire from the IEC to the switch and the fuse is the line wire - it is marked L on the IEC jack. The Neutral wire goes directly to the transformer, it is marked N on the IEC jack. Wire the ground lug on the IEC jack to the chassis - I soldered it to a lug and connected it between the nut and screw holding the transformer down. Make sure that this ground wire is electrically connected to other screws in the chassis. (check the screws because the black paint on the moog and brown powder coat aren't conductive - only screws going through the metal make contact with the chassis metal). This is an important safety feature - if a hot line wire came loose and touched the metal chassis, it would be shorted to ground preventing the case from electrifying (it would also trip the circuit breaker).
COVER ALL BARE WIRE CONNECTIONS IN HEAT SHRINK TUBE OR ELECTRICAL TAPE to prevent accidental shorts or possibility of touching a live wire!!
6. Test it -
Smoke test: Turn on the new AC switch to allow power to the transformer - don't turn on the rogue's on switch. Verify that 24V AC is present at the positive power wire going into the circuit board. Now, turn on the rogue's switch. The LED should light up. Turn both switches off after a few seconds. Make sure the heat sinks on the voltage regulators aren't hot. If too much current or voltage is being drawn, they will get very hot in seconds.
Conservative Test: If you are freaked out about damaging your rogue, you can disconnect the two red wires and two black wires connecting the main board and the small power board. This will virtually eliminate the possibility of damaging voltage going to any sound circuitry. Power it up. Now, the connection points for the black wires should read -12V on the multimeter. The connection points for the red wires should read +12V. Test relative to ground, which is where the green wires connect to the small power board. If all is good, re-solder the black and red wires into the right places.
Put it back together.
Test test: Plug it into an amp, power it up and play. Is it working?
Power In - J5 is a 3.5mm jack, like a mono headphone jack. When plugged in, AC electricity from the wall-wart enters the circuit - tip to a switch (marked power sw1) and the sleeve goes directly to the synth's ground. When powered on, the 24V AC goes through the non-grounded lead and gets turned into positive and negative DC by CR8 and CR9. The capacitors C37 and C38 buffer and filter ripple out of the DC power. The 78M12 regulates the power, making it a steady +12V. The 79M12 regulates the negative power supply and creates a steady -12V. The ground, shown in between the positive and negative regulators and capacitors provides the reference point for power regulation.
Approach:
We want to replace the power in jack with an internal transformer that turns 110V AC into the 24V AC the Moog wants to see. We also want to IMPROVE this power supply's quality by adding further filtering to the power supply and providing a three-prong, fully grounded outlet and a fuse to protect the circuitry and ourselves.
Any audio gear only sounds as good as its power supply -- a bad power supply is to blame for almost all cases in which audio gear picks up 60 cycle hum and is often responsible for transient interference and spikes - hiss, crackle, radio interference, etc. Some devices like power amplifiers are more forgiving of ripple and spikes in the power supply, but synths are CERTAINLY not. The Moog Rogue, being a lower priced model, has a few corners cut on the power supply. The Rogue power supply is arguably the weakest part of this synth. We're going to change that...
The filtering and regulation shown in the schematic above is good, it eliminates ripple and filters well. The rectifier is also fine.
We are going to replace the transformer in the AC Wallwart with a Chassis mount power transformer. We are also going to add some additional filtering to the AC line power. A 3 prong earth ground or safety ground, and a fuse to protect the synth, our house wiring and ourselves from electrical accidents or damage.
Here's what my new, modded design looks like:
Calculating Fuse Rating:
The synth requires about 200mA of AC current. Since we're fusing the primary (to protect the transformer as well), there will be a different current draw here than on the other side of the transformer. The calculation for the transformer ratio is V(primary)/V(Secondary). 120V / 24V = 5 --- so, current is 1:5 (primary:secondary). So, 200mA load on the secondary is 200/5 = 40mA on the primary side. Pretty small. So, a .1A fuse should be good. This should blow if more than 500mA is drawn by the load -- which is FAR less than can damage the circuits of the synth.
The Project:
(Only do this if you understand the risks, otherwise, just read and
learn!)
| Warning: This
project exposes the
project builder to potentially lethal line electricity. Only proceed if
you KNOW that you know how to deal with high voltages. Advice: I am not
perfect, and not every synth is the same (different
rogues have different circuit boards!). Use the schematic as a guide
along with your knowledge of electronics - this is not a step by step
for people without any grasp of electronics.
|
If you really want this internal power supply on your Rogue, but don't have the chops to do it yourself, you can contact me - lparker@calarts.edu. Maybe I'll do it for you...
1 24V AC Chassis Mount Transformer that will fit inside the case.
1 Fuse holder
1 .1A fuse
1 IEC Power entry with RFI / EMI filter
1 Power Switch (rated at least 120V AC SPST or DPST) - (or get an IEC Power entry unit with a power switch included in the unit)
Wire
Heat Shrink Tubing
Electrical Tape
Tools:
A Power Drill
Drill Bits (a stepper unibit is HIGHLY recommended)
Screwdriver
Multimeter
For cutting square metal hole - Metal File, Saw (scroll saw or jewelers), or nibbling tool depending on method used (strategies are shown here).
1. Open the Rogue. Unscrew the bottom screws, the two in front on the side panels beside the keyboard and the LOWER screw on the back. Don't unscrew the screws holding the circuit board in place (these are higher up on the back). Now, you can do this mod without removing the circuit board, but I suggest removing it to eliminate the chance that you'll damage it. Also, you can unplug the molex connectors that join the top chassis with the keyboard (Be sure to note which way they go so you don't plug them in backwards when done {I draw a red line on one side of the molex plug and jack. When I reconnect if the two lines don't reconnect I know I oriented them wrong}). It's much easier to work with the synth if the two pieces are separated. Remember, you need to take off all the knobs to remove the circuit board.
Optional - De-solder and remove the old power jack from the circuit board. A good thing for safety, accidentally plugging in the old wall wart and the new supply simultaneously could be VERY bad. I would eliminate the chance by getting rid of the jack. Marvel at how cheap the component is.
2. Place the transformer - It's heavy, so it's a good idea to center it to keep the instrument balanced. Make sure it fits - there is lots of room, but measure first and make sure that the case closes without the transformer touching the circuits above before you drill any holes.
Mark the drill points for the transformer mounting with a sharpie or scribe.
Center tap the points you marked.
Drill the holes (size depends on the transformer, but approx. 1/8" bit ordinary) - be sure to hold the chassis down firmly or clamp it, use tapping fluid or lubricant to cut the sheet metal. (Things like WD-40 or even Olive oil will lubricate a little if you don't have tapping fluid, but don't cut it dry).
Line up the transformer and place 4 small bolts through from the outside of the case. Tighten a nut down to secure the transformer to the case. (4-40 bolts and nuts were used here, but bigger holes might use 6-32 or larger).
3. Place the IEC entry, the fuse holder and the new AC switch (if applicable).
Mark the square hole you need to cut for the IEC plug entry unit. Use a sharpie or metal scribe. Make sure it's within reach of the transformer's primary leads (usually black).
| How to Make a Square Hole in
Sheet Metal: 2 methods in order of preference (other methods exist too): |
|
Using Drill and
Scroll Saw (or Jewelers saw)
- Scribe the outline of the square. Make it exact or just a bit smaller than you need (it's best to file it larger than make a hole too big). - Center punch 4 points to drill just to the inside of the corners (about 3/16" to the inside of the scribed outline) - Choose a drill bit (just large enough to fit a scroll saw blade through - or jeweler's saw) - 3/8" for my scroll saw blades. - Drill 4 holes at these points - ideally the edge of the holes should meet with the boundaries of the outline, but not go over) - Using a metal cutting blade, insert the blade through the hole, tighten it to the saw and saw between the drill holes, outlining the square. Lubricate with beeswax or fluid. - You might have to re-insert the blade at each 90 degree turn, but the drill holes provide room for this. - Use a metal file to clean up the edges and square it up. |
|
(Using Just a Drill
and a Metal File)
-Scribe the outline of the square.-Find the center and center punch it there. - Drill a small hole as a pilot hole. - Now, drill a larger hole using a stepper bit or successively larger drill bits. Make sure the metal is CLAMPED down to the surface and you lubricate with tapping fluid. making big holes in sheet metal can twist the metal and pull up on it, ruining the hole and possibly swinging the sheet metal in the air (dangerous). - Stop when the hole's edge reaches the edge of the scribed square. - Use a file or a nibbler to make your round hole into a square. (I strongly recommend a stepper type drill bit for drilling large holes like this in sheet metal) |
 Filing the hole square after
drilling the corners and cutting between them with a scroll saw. |
4. Drill or punch the hole (or holes) for the fuse holder and the AC switch. I chose to use a chassis mounted easy access fuse holder. I drilled a 1/4" hole and used a 9/16" Greenlee punch to make a clean hole (a stepper bit will work well too - I just happen to have the punch).
Punching the hole for the fuse holder
with a 9/16" Greenlee Chassis punch. (Don't forget to lubricate).5. Wire it -
Moog to transformer -- Look at the picture below and then use a multimeter to find the exact points! Circuit boards vary. This is why I don't have a close-up.
1. Find the point where the TIP of the wall wart connector connected to. Follow the trace to the switch - it should lead to the center pole of the power switch. Solder the wire into the hole / pad left when you removed the wallwart jack or the switch's pad. This is the positive supply.
2. The green wires on the smaller circuit board are all ground. Solder the a negative wire lead to one of these points.
3. Check it! Using the continuity checker with your multimeter make sure the negative lead you added is connected to ground. Check it in a few places - with one lead connected to the loose end of the negative wire you attached: check that it is has connection / continuity with the sleeve of the audio out jack, other green wires on smaller board, the screws on the small board that connect to the heat sinks on the voltage regulators (all these are connected to ground). Next, make sure that there is no connection to the positive wire you just connected.
4. Find the white/red striped wire from the main board to the smaller board. With the rogue's power switch off, there should be no connection to the new positive wire. With the switch on, there should be continuity.
Finally, use the schematic and your eyes as a guide. Make sure there aren't solder bridges on the new connections.
Wire the transformer, IEC plug and fuse according to my schematic. Make sure that the wire from the IEC to the switch and the fuse is the line wire - it is marked L on the IEC jack. The Neutral wire goes directly to the transformer, it is marked N on the IEC jack. Wire the ground lug on the IEC jack to the chassis - I soldered it to a lug and connected it between the nut and screw holding the transformer down. Make sure that this ground wire is electrically connected to other screws in the chassis. (check the screws because the black paint on the moog and brown powder coat aren't conductive - only screws going through the metal make contact with the chassis metal). This is an important safety feature - if a hot line wire came loose and touched the metal chassis, it would be shorted to ground preventing the case from electrifying (it would also trip the circuit breaker).
COVER ALL BARE WIRE CONNECTIONS IN HEAT SHRINK TUBE OR ELECTRICAL TAPE to prevent accidental shorts or possibility of touching a live wire!!
6. Test it -
Smoke test: Turn on the new AC switch to allow power to the transformer - don't turn on the rogue's on switch. Verify that 24V AC is present at the positive power wire going into the circuit board. Now, turn on the rogue's switch. The LED should light up. Turn both switches off after a few seconds. Make sure the heat sinks on the voltage regulators aren't hot. If too much current or voltage is being drawn, they will get very hot in seconds.
Conservative Test: If you are freaked out about damaging your rogue, you can disconnect the two red wires and two black wires connecting the main board and the small power board. This will virtually eliminate the possibility of damaging voltage going to any sound circuitry. Power it up. Now, the connection points for the black wires should read -12V on the multimeter. The connection points for the red wires should read +12V. Test relative to ground, which is where the green wires connect to the small power board. If all is good, re-solder the black and red wires into the right places.
Put it back together.
Test test: Plug it into an amp, power it up and play. Is it working?
|
David's Rogue, fully wired:
(Notice that there is no
AC switch - this
means that David must unplug his rogue when he is not using it,
otherwise line voltage will always reach the transformer. It isn't
dangerous, but it's not kosher and wastes electricity to leave the
transformer plugged in - even without a load.) Also notice that I used
a transformer with multiple secondaries. These extra secondaries are
not
being used now, and are insulated with heat shrink. In the future,
we might add another power supply with these leads to power
some lights or special effects. |