Switchable Split Mod DIY directions...

[sean]

(July 2017 edit:  skip to the bottom of this thread to see updated wiring diagram, and other improvements.  The update is much better than my work in 2008.)


Here are the complete directions for splitting the pickup rail to provide a bass output and a lead output, and adding a switch to change from whole-harp to split-harp.  It took longer to create the drawing than it took to do the mod, but I had fun doing both tasks.

Before I started the project, I had a few ground-rules:
1.  I won't drill any new holes in my piano's name board or chassis.
2.  I won't modify the Volume and Bass Boost circuitry on the name board.
3.  The Volume and Bass Boost controls must still work after the mod.
4.  I did not want to re-wire the RCA jack on the pickup rail.
5.  I did not want to mess around with any of the ground wires or foil tapes.
6.  I didn't want to spend much money.  Twenty bucks max.
7.  I wanted the mod to be 100% reversible.  Minimally intrusive surgery.

Take a look at the drawing below, and I'll explain what I did.

The first drawing shows the pickup rail circuit as it ships from the factory, and then the circuit split into two outputs.   (The goal is to switch between the two at will.)

[Photo deleted by lame photo-hosting company.  PM me if you really want to see it.  Diagram below is better anyway.]


Where to Split

Divide the pickup rail into two sections by cutting the jumper wire opposite an existing break (otherwise, you will orphan a pickup).

Solder your take-off wires to these freshly clipped ends.

[Photo deleted by lame photo-hosting company.  PM me if you really want to see it.]

Temporarily remove a tonebar assembly on either side of the split to give yourself room to work.


Make it switchable:

The drawing below shows you how to wire a three-pole double-throw switch to select between the whole harp and the split harp configurations.  The switch is shown from the back side with the toggle pointing away from you, and turned so that the toggle flips from left to right (NOT up-down). 

Since the switch terminals are a three by three grid, you may have some confusion about how to hold the switch so that it matches my diagram.  Don't use the visual depiction of the solder lugs in my drawing as the guide for holding your switch in the right position!  Use the movement of the toggle from SIDE TO SIDE be the indicator of proper switch position.

The wires are drawn as thin or thick ONLY to make it clear that they do NOT connect when they cross each other in the drawing.

[Photo deleted by lame photo-hosting company.  PM me if you really want to see it. ]


Here are the steps you would take to put this together:

DON'T CUT THE WIRES ON THE PICKUP RAIL UNTIL THE LAST STEP!  This way, if you have any interruptions in the construction process, your piano will still be gig-ready.

1. Buy a small 3PDT switch.  3PDT means three-pole double-throw.  You want a miniature toggle switch without a center-off position.  You want ON-ON operation, not ON-OFF-ON or ON-NONE-ON.
I got my switch from ebay (search for "3PDT toggle M302" and you will find the exact item and seller I used).  (Radio Shack did not have a suitable switch.)

2. Get a panel-mount female RCA jack.  I used a cheapie from Radio Shack. Four bucks for a bag of four.  You also need a 1/4" jack.

3. Get a good quality three-foot RCA-to-RCA male-to-male cable and cut it in half (you need about 18 inches). Strip and dress the cut end so that you can solder the center conductor and shield braid. This cable will go from the RCA jack on the pickup rail to the splitter switch.

4. Get three feet of top-quality shielded microphone cable.  You do NOT need rugged thick mic cable that you would use on stage, just any two-conductor-plus-shield cable.  I used Belden 8451.  This cable will go from the split point on the pickup rail to the splitter switch.  You will not need the shield conductor at the pickup split point, but you must connect the shield conductor at the other end of the cable to the ground point of the splitter.

5. Choose a little box to build it in.  I used a plastic box from Radio Shack, but it isn't rugged or sturdy.  (I think I will get a diecast aluminum Bud box. I want to build it in a tiny Bud CU-123 or CU-470.)  You will have to drill a 3/8" hole for the output jack, a 1/4" hole for the switch, a 1/4" hole for the RCA jack, and a small hole for the two cables to exit the box.  Mount the switch, 1/4" jack, and RCA jack in the box, and screw them in tight.

6. Do not solder anything until you have ALL the wires routed and pinched tight to the terminal lugs.  Get a few inches of insulated jumper wire and make the connections on the switch as shown in the diagram.  When you have all the connections in place, and have double checked them for correctness, solder them for perpetuity.  Solder the connections at the RCA jack and 1/4" inch jack. 

You should now have the whole assembly ready for action, except that it is not connected to the piano.  It should look like a box with two cables hanging out: one cable has the RCA plug, and the other will eventually be soldered to the pickup split point.

7.  Now is a good time to mount the assembly on the piano.  I mounted mine using the little screw at the corner of the control panel (the panel that holds the bass boost and volume pots).  This panel is mounted to the name board using four #6-32 screws.  I removed the upper left screw, and used a longer #6-32 screw.  (I drilled a tiny hole in the bottom of my plastic splitter box, pushed the long #6-32 screw though the hole, and held it in place with a piece of tape.  Then I closed up my splitter box with the #6-32 screw still protruding proudly out the bottom.  I carefully inserted it in the hole in the nameboard, and tightened a nut to hold the box securely in place.)

8.  Now you can get ready to connect the splitter circuit to your piano.  Protect the keys from damage with a thick bath towell (I cover them with a wooden board).  You do not want any solder to fall off your soldering iron and splatter onto the keys.  Better safe than sorry.

9.  Disconnect the grey RCA cable from your piano's RCA jack at the back left of the harp, and plug it into the RCA jack on the splitter box.  Connect the new RCA plug from your splitter box to the RCA jack on the harp.  Locate the place where you want to split the pickup rail, and gently snip the wire right at the midpoint between the pickups.  Carefully route the cable from your splitter box to this point.  If there is a lot of extra cable length, you can trim it off.  Strip the wires back, and gently solder them as shown in the diagram, and also shown in this photo:
[Photo deleted by lame photo-hosting company.  PM me if you really want to see it.]
Take-off wires soldered to pickup rail.

Notice that I didn't bend the ends of the wires and hook them together.  The straight wires are much easier to un-solder if I ever want to remove the splitter and clean up after myself.

If you are going to gig or move your piano, you should secure all the cables with wire ties to keep them from flopping around or tugging on the pickups.

Replace the piano top cover, and you are done!  Plug in two amps and play.



Here are some photos of my prototype and finished project.

Prototype and cable connections:
[Photo deleted by lame photo-hosting company.  PM me if you really want to see it. ]
This photo gives you a clear idea of how the circuit inserts into your piano signal path.


Splitter box mounted on name board
[Photo deleted by lame photo-hosting company.  PM me if you really want to see it. It was kinda ugly.]


The regular output and controls still work.
[Photo deleted by lame photo-hosting company.  PM me if you really want to see it.]
Even without drilling the name board, the splitter box can stay out of the way, but it is handy when needed.   

If you made a serious committment to this mod, you could drill holes into the name board for the switch and the 1/4" jack.  You could replace the panel-mounted RCA jack with a female RCA cable, and secure the connections with wire ties, and tuck the wires next to the harp support.



If you want a shopping list for the supplies you need to make this mod, here ya go:

1 each 1/4" jack
1 each panel-mount RCA jack
1 each miniature 3PDT on-on switch
1 each three-foot RCA male-to-male cable (well, you actually only need half of this cable)
3 feet of mic cable, belden 8451 or similar
1 little box and a mounting screw


Any questions?

- Sean

[Rob A]

What effect does this have on signal levels? If you disengage part of the pickups, do you get more level from the ones that remain?

Great writeup BTW.

[sean]

You actually get a tiny (but noticable) boost in signal levels, because you are taking some resistance (and inductance) out of the signal path when you bypass a big group of pickups.

25 pickups might amount to 480 ohms.
[Sean edited his mistaken calculation.]

[sean]

I am a little disappointed about how the diagram looks when posted.

The png file just doesn't show enough detail...  I'll try to post a tiff.


BotoPhucket won't let me post a pdf file.  Anyone know a free hosting site that will post a pdf?

Sean

[Rob A]

As I recall the normal configuration on a 73 gives about 1500 ohms seen at the RCA jack.

Each pickup is ~180, and it's 24 series-connected groups of 3 in parallel. (plus one extra that I'll ignore)

3 in parallel is 60 ohms, so 24*60 gives you the 1440 ohms.

If you split the harp in half I'd expect 2 groups of 720 ohm. So I'd sort of expect a level boost on the order of 3dB. I was just curious how theory and practice line up in this case.

[sean]

Yikes!  We BOTH goofed up the math:

24 pickups would be a series of eight groups of (three in parallel).

Eight times 60 ohms gives you only 480 ohms!



Sean

[garagebandking41]

you could fit a pot in there to control the bass volume or even duplicate the stage controls right? Looks pretty nifty. You could at least try and match the volumes with that set up...?...Very nice job btw! I'm taking my circuits classes in a semester, maybe then I can catch up with you guys eh.

edit:

I ask because I set up the bass sections' timbre and what-not differently than that of the treble: To have more bass usually, and a little closer to the pickups, So i've always wanted to have a little volume/bass control on that section so i could change depending on if I'm doing left handed bass or just comping myself. I'd like to just split the rail and add a second set of stage controls but still go into the one output 1/4". That's achievable with this mod, correct?

[Ben Bove]

What a great write-up thanks for this post!

[Rob A]

I'm not sure where 25 pickups comes from. None of my math was about 25 pickups, just 73 split in half.

[sean]

I'm not sure where 25 pickups comes from. None of my math was about 25 pickups, just 73 split in half.

Oops.  Sorry Rob.  Your calculations are correct for a 73-note piano (one group of four and 23 groups of three pickups).

My harp reads just about exactly what Rob predicts with my ohm-meter.

1440 Ohms for 73 pickups.

My bass split of 25 pickups reads 463 Ohms.

[sean]

Hey GBK41,

I didn't personally think that a volume control on the bass split was needed, because I can control it on the AMP, and I could control the overall balance between the left and right hands by tweaking the volume control of the right hand voice.

...but you certainly could add passive volume and tone controls to the bass voice just like those found on the name board.  

Also, you could indeed have both outputs go through a simple voltage-divider mixer and then to one output, but then you are asking for noise and lower signal output... AND you would be giving up the one cool feature this split allows you to do:  different effects on each voice.

My desire is to run the BASS OUTPUT into an amp set for:  no reverb, no effects, EQ set to favor the low midrange (don't need super lows, don't need much high-end clarity), powerful volume but no distortion, and
...run the LEAD OUTPUT into a preamp that has an effects loop bursting with options (chorus, phaser, wah, whatever), and then into an amp set for some reverb, EQ might finally include some low midrange, medium volume when the nameboard knob says 7.


With the bass register removed from the main Rhodes sound, we can finally use the bass and midrange EQ knobs on our amps at settings above 3 without wading into the mud.



If you want tone control over each voice, and volume control over each voice, and the flexibility of one output plug... pretty soon you might as well buy the $400 high-end active preamp splitter kit from Vintage Vibe.

Sean

you could fit a pot in there to control the bass volume or even duplicate the stage controls right? Looks pretty nifty. You could at least try and match the volumes with that set up...?...Very nice job btw! I'm taking my circuits classes in a semester, maybe then I can catch up with you guys eh.

edit:

I ask because I set up the bass sections' timbre and what-not differently than that of the treble: To have more bass usually, and a little closer to the pickups, So i've always wanted to have a little volume/bass control on that section so i could change depending on if I'm doing left handed bass or just comping myself. I'd like to just split the rail and add a second set of stage controls but still go into the one output 1/4". That's achievable with this mod, correct?

[Mark II]

just wanted to say: Sean, brilliant post and awesome documentation

kind regards
Mark II

[garagebandking41]

Thanks! Yeah I assume that a split mod is for that purpose, which is very useful.  I'm kinda too specific and less functionality when it comes to that. Maybe i just want too many knobs to mess with, hah.

You could probably sell your split rail device, very awesome and neat. I'd buy it seeing i don't have the 400 dollars!

[kineticturtle]

this is awesome! Thanks so much! I'm definitely going to dig into this project at some point soon... when my other 80 projects level off...

It's got me thinking, too, about doing this with a movable split point with a three-way selector switch - the options being E-F 32-33 (like yours), A#-B 38-39, and E-F 44-45

My only fear in doing that would be creating too many little split up sections of pickups with wildly varying resistance. Any thoughts on how I would avoid that?
Or are the sets of pickups already running in parallel, so it wouldn't matter?

It's too late in the day to be wracking my brain about this. Good thing all I have to do tonight is play drums!

[sean]

Has it really been eight years since I started this thread? 

A few weeks ago, I plugged in my split-modded 1981 Mark II to a pair of amps.  After playing with the bass separated for a while, I toggled the switch back to the "whole harp" position, and I was greeted with a nasty buzz from the amp connected to the bass output.  DOH!!  That is a design flaw!

So I decided to revisit the design of the split mod, and here are a few changes:

1.  Change the switch to a 4PDT (four-pole, double-throw) switch, and use the extra pole to silence the bass output when the switch is in the "whole harp" position.

2.  I still refuse to drill into the original Mark II control plate, but I have decided that the little box hanging off the name rail is goofy.  My solution is to simply get an aluminum panel to replace the original control plate.  I went to my local Metal Supermarkets (I s**t you not, there is such a place), and got a few panels (1.969" x 16.250") for ten bucks (14-guage (1/16" thick) 5052 or 6061 aluminum).  There are Metal Supermarkets in 75 spots the US and Canada, see www.metalsupermarkets.com (not www.metalsupermarket.com).  Looks like MetalsDepot would also be a good source, www.metalsdepot.com; or even OnlineMetals.com.  Anyway, my intention is to drill it, paint it black, and mount it on the namerail using the original screws.

3.  GarageBandKing was right.  The bass output needs a volume control.  I went to the online tropical jungle, and got a handful of 10K-Ohm audio-taper potentiometers.

4.  I don't have a good way to label the panel.  No silkscreen or stencil, and tape labels won't cut it.  So I decided to get Fender 72 Telecaster guitar knobs (two volume, two tone), make sure the knobs match your potentiometer.  I got knobs with a setscrew.  I will put the volume knobs, well duh, you know where; and I will put a knob marked "tone" on the Bass Boost control.  I got the knobs at the online tropical jungle as well.

5.  The "ground" or connector sleeve on the bass output cannot touch the chassis ground.  So I have to isolate the Bass Output 1/4" jack from the name rail.  My first idea was to buy a bit of ABS guitar pickguard material, and make a little panel insert.  However, I think I will either use a Neutrik NJ3FP6P-BAG plastic isolated jack, or I could simply use a Switchcraft jack with old-fashioned insolation shoulder washers.  Or I could use a flimsy plastic Switchcraft jack.  I think the Neutrik is ugly, but I am afraid that the fibre shoulder washers are not durable enough.  Oh, now I can get nylon shoulder washers.  That is a plan: switchcraft jack with nylon shoulder washers.  This is foolishly wrong.  The ground on the bass connector can certainly touch the chassis ground.  I don't know what sketch I was looking at that convinced me they should be isolated, but it just isn't so.

6.  The cable that comes from the split point on the harp should NOT be soldered directly to the switch, because you cannot remove the name rail from the piano for easy maintenance.  I think I will use an RCA connector, but I haven't decided if I should mount it (isolated) on the back of the control panel; or should I just leave it as a cable end connector, and tidy it up with wire ties?

When I finish, I will create another complete writeup with photos.

Sean

[sean]

I finally finished this project on my 1981 Mark II.


The wiring was pretty straightforward, and is detailed in the attached pdf.  The pdf should print better than the image below.  (Looks like the attachements only show up if you are logged into this site as a named user.)




The control panel itself took a bit of patience.  The attached pdf shows cutting and drilling dimensions. 
(See the entry above from December to find out where I bought the aluminum panel cut-to-size.)

My first attempts looked terrible, because the glossy paint didn't look right with the name rail.  It looked cheap and nasty.  So I drilled another panel, and painted it with self-etching primer and then a matte black top coat.  It came out looking beautiful.  It matches the name rail, and it looks right at home with the whole piano.  So don't use glossy, appliance enamel, satin, or flat black paint.  Buy matte black spray paint. 

The mounting holes at the corners of the control panel didn't match up very well with my namerail.  If I do it again, I will try to transfer the hole locations from the namerail directly onto the sheet metal for the control panel (instead of trying to measure and mark). 

The Telecaster knobs worked out perfectly.  They look great, and they look period-realistic for a 1970s or 1980s piece of gear.  It isn't obvious in the photos attached, but it is very clear to the player which ones are volume and which one is bass boost (the knob marked "tone").

Putting a connector on the wires that come from the split make the assembly easier, because you can do all the soldering work on the back of the control panel on the workbench.  Install the control panel into the name rail, mount the namerail onto the piano, then plug it all together.  You can unplug and completely separate it when you want to remove the name rail to work on the piano action. 

And the most satisfying thing about doing all this work is:  the end result is very fun to play, and it is extremely useful.  The volume knob on the bass output makes it very easy to balance the left hand and right hand voices.  It is really easy to play one song where you want the bass notes with a different EQ setting or effect (phaser or auto-wah), and then the next song (or song section) with the whole harp together with a more conventional sound - with just a flip of the switch, and sometimes a tweak of the volume knob.  It makes the piano even more versatile, and definitely feels like an enhancement.

Sean

[David Aubke]

Amazing how a seemingly simple modification can grow in complexity when the details are getting worked out.

When I need to reproduce the indicator arrow on the metal-flanged knobs, I use a sheet of Letraset. In addition to all of the letter characters on each sheet, there's also a big blank area at the header and footer from which you can cut custom shapes. They look dead-on original if you cut them properly and they hang on pretty well.

But now I see new Letraset sheets are apparently unavailable. But there are other dry-transfer products.
https://imagetransfers.com/blog/how-our-dry-transfers-different-from-letraset/