Some spinets (in particular, those with percussion, like the M3's) already have some of the key contacts which you need for AddingFoldbackToASpinet. (These contacts are required for triggering the Percussion.) In this case, one can add partial HarmonicFoldback (eg. only on the upper drawbar on the upper manual) without adding any extra parts.
(It's not completely clear why Hammond didn't do this in the first place.)
Adding Poor Man's Foldback to an M-3
These instructions were posted to the HamTech mailing list (on 6 July, 1999) by SteveBlair.
Here's a detailed description I put together after doing this on my M3. Lots of thanks to Lars Mikael (CaptainFoldback) for this idea.
- Remove the music rack and music rack base.
- Remove two large bolts underneath the manuals that hold upper manual in place.
- Remove the "can" for the bass pedal drawbar and lay it on the generator. No need to disconnect any wires.
- Remove the generator cover to give you extra room to work, but lay a large towel over the generator to keep any screws or parts from falling into the generator.
- Raise the upper manual as much as possible and prop it up with blocks of wood.
- Optional: Remove all the keys by removing loosening the small bolts for each key from behind and lifting the key up. I'm not sure that you absolutely need to remove the keys, but it gives you more room to work. You can also clean the keys and underneath them. When you put them back in, make sure the small washer is on the outside, or the key support will not seat properly.
- Remove the few screws along the back side and under side of the upper manual that hold the cover on. You will then see all the small white wires.
- Now move to the front of the organ and find the bundle of white wires that are all soldered together on the extreme right underside of the upper manuals to a ground lug.
- (Remember to prop the manual up as high as possible so you can work in this area.)
- You'll see the large black generator wires attached to the front strip and the white wires attached to the back side of the same strip.
- Unsolder the bundle of white wires then use a continuity test to determine which wire goes with which key. There are 18 wires corresponding to the 2nd from highest G up to the top C. Clip one end of the continuity meter to the 1' drawbar end and the other to one white wire at a time. Then press each key until your meter moves. I did it the opposite way by weighting down a particular key then touching each wire until I found the right one. If the keys are removed, you need to press each "switch". I labeled each switch with a pencil so I could keep track.
- Then carefully route the correct wires to the correct frequency terminal (one of the last 12) and resolder. Keep in mind that for 6 of the terminals you will solder 2 wires each. I worked from the right-most terminal (highest frequency) to the left. The first 6 terminals get one wire, the next 6 get two wires. The wires have cloth insulation and I found the best way to strip them was to burn the insulation with a soldering iron, then gently scrape with a sharp matt knife. After you solder and make sure everything works, then cut off the excess length.
- (See Detail Wiring Chart below, then return here.)
- You can test each wire after you solder by starting the organ and pulling out only the 1' drawbar. Then press the appropriate key. Make sure everything is clear of the generator before it starts spinning.
- After everything is soldered, reassemble everything, and you're ready to go. Make sure each key support seats properly when you tighten down each screw. Two small dots make sure it aligns properly. You can make some fine adjustments for key alignmnet even when the keys are "seated". But make sure that little washer is not behind the key flange or it won't seat properly.
- This Poor mans Foldback mod will not affect the percussion as someone asked.
Again, I want to give full credit to Lars for this mod. I love it and don't know why hammond didn't make it a stardard feature.
Enjoy! --SteveBlair
Detail Wiring Chart
Here is the complete connection listing. I will start from the highest C and work down.
Key Frequency Lug
----- ---------------
Highest C 85 <==7th lug from right side
B 84 <==8th lug ...
Bb 83 etc
A 82 etc
G# 81 etc
G 80 <==12th lug from right side
F# 91 <== first lug on right side
F 90 <== 2nd lug from right side
E 89 <==3rd lug ...
D# 88 <==4th.....
D 87 <==5th....
C# 86 <==6th....
2nd Highest C 85 <==7th lug from right side
B 84 etc
Bb 83 etc
A 82 etc
G# 81 etc
G 80 <==12th lug from right side
From this list, you can see that the frequencies "foldback" at the 2nd to highest G, then again at the highest G. Therefore, the wires for these two notes should be attached to Frequency # 80, which is the 12th lug from the left. That's what foldback means, the frequencies simply repeat because you've run out of new frequencies above # 91. So, with only the 1' drawbar pulled out, when you press any of the highest three G keys, you get the same tone, or frequency # 80.
Make sense?
Also from the chart, you can see that you only solder 1 new wire to the 6 rightmost lugs, and 2 new wires to the next 6 lugs.
TopicModification
