Vibrato system in L100 is a real drawback. While vibrato sounds ok, chorus sounds really bad.
I absolutely love the original Hammond's chorus vibrato and decided to change the vibrato system rather than buy new organ. There are 3 steps of doing it.
What you need:
- synchronous motor from T-series (they have the necessary pulley at the other end)
- drum vibrato scanner with driving belt and mounting brackets
- vibrato delay line from M or T series
Those may be expensive here in Europe but it is worth the money! It is best to contact Hammond parts sellers on eBay and ask them about those items. They usually have a broken T or M for spares. That's how I got the parts anyway.
Why drum vibrato scanner and not the famous 'pie' shaped one? In L100 there is enough room to fit the first one next to the motor. Thus you donít have to worry how to drive the scanner with a separate motor.
Before you perform this modification check Kon Zissisís vibrato mod available here. It saves money and time! You may find that the vibrato produced by modified vibrato amplifier is good enough for you.
# Step 1
Put all the parts in place. Make sure to mark all the wires - it could save you some time and work later.
Note that one side of the scanner must be pulled out of the brackets as the distance between two pulleys would be too short (unless you find a different, shorter driving belt).
Drum vibrato scanners however have one major flaw. They can be noisy. And there is really nothing to make them work quieter. You will just have to get used to it.
My vibrato line replaced vibrato amp and could be screwed to the back of upper manual.
# Step 2
I bought all the parts but I couldn't have succeeded without a help from a technician who built a recovery amplifier for me. Many thanks to Simon from OrganForum.com!
Simon discovered that the scanner needs to be driven with enough power to preserve low frequencies that would otherwise be filtered out and lost. In L100 the signal is too weak to be used with vibrato scanner therefore a recovery amp is needed. He built and tested his DIY circuit and sent it to me.
Recovery amplifier schematic
Use screened cables and some metal box in order to eliminate hum problems.
Proceed with caution as there are high voltages in the recovery amplifier!
You can use 250V from the preamp unit.
Adjust VR1 and VR2 if there is too much distortion in the signal. Press multiple keys and see if any clipping appears.
# Step 3
Now all you need to do is to connect all the pieces together.
If you have vibrato line from M100 or T500 - you will need one 4-pole changeover (4PDT) switch to be able to switch between small and normal vibrato.
If you have vibrato line from model M, M2 or M3 you will need a 6-pole switch.
Depending on what vibrato line you have got, you need to connect the scanner and the vibrato line as shown on the schematic.
You can find vibrato circuits in the manuals: M-series on pages 62 to 75; T-500 series on page 53.
Your switch should have three rows of pins. You will change only 4 or 6 out of 8 wires (see the schematics). The middle row should be connected to the scanner. One of the remaining rows should be wired to small setting and the other to normal. You can remove the pilot light which is an unnecessary decoration and put the switch in its place. Now you can easily change between small and normal vibrato.
Now it's time to make a switch to turn vibrato on and off. To do it you would need to switch between vibrato and non-vibrato signals. It means additional changeover switch and RCA divider. But what about those three nice flip tabs that are now left unused? I was thinking about it for a while when I got that nice little idea.
Straight signal can be mixed with vibrato by putting a resistor in the circuit. It means that if you start changing the value of the resistor you can either add more or less straight signal.
- To add less, you need to use lower values (and when you reach zero you get clean vibrato).
- To add more, you need to use higher values (and after reaching infinity the signal becomes 100% straight).
Infinite resistance means broken connection. That's why I used Chorus tab to break the connection in the circuit.
However after breaking the circuit there is still a certain amount of vibrato. Very little but noticeable. I'd say 1%, maybe a bit more. I decided to use it though. This solution is Ďcleaní and it doesn't require any additional switches.
To change between vibrato/chorus you need to do the same but instead of breaking the connection, bypass the resistor. Use one of the remaining tabs for that.
It would be nice to have screened cables with RCA plugs to make nice connections between the new vibrato system and the preamp. Once you got everything in place and wired up you can connect IN2 to BK socket and OUT1 to BN socket in the preamp box.
You may need to ground the motorís housing as well as scannerís metal rods to get rid of any static coming from the motor.
If you have done everything correctly, you can enjoy your new vibrato!
Here is another way of adding a vibrato scanner (as done by Michael):