Volume/expression pedal for roadcased C3

[wayshot]

Hello!

I've been working a bit on a chopped/roadcased C3 lately, it's been put in a studio by the owner after many years of storage. It's a two-case design - manuals and preamp in one box and generator, scanner and line box in another. There's no swell pedal, linkage or arm, and a volume pedal has formerly been used between a 1/4" jack output and a Leslie interface box. I recently wired the organ and a Leslie 145 with Speakon-8 contacts, according to a local wiring standard.

The owner does have several Yamaha FC7 pedals around and wishes to use one as a volume/expression pedal. I've tried wiring it between the AO28 terminal F (volume soft) and ground, but it doesn't work optimally - most of the volume change is on the bottom 20% of the pedal travel, and there's distortion as bottom is reached. I also tried wiring it between one G and ground, resulting in very little change in volume from bottom to top.I currently research other ways of wiring up the FC7.

One idea is wiring it between the tone control wiper and 12BH7 grid, either as a straight voltage-divider volume control or as a bridged-T notch filter like the LDR on E100, H, L, R or T organs. Does any of you have suggestions or better ideas? Using a bicycle brake cable or similar for swell control is impractical because of case design and missing parts.

[enor]

RC servo, small controller board, expression pedal:

[Wes]

Remember that an expression pedal is not a volume pedal. Any voltage-divider solution will be severely sub-optimal.

Magnus' solution is awesome.

Wes

[wayshot]

Wes: I know the difference. The owner could do with a simple volume control, but would prefer a proper expression pedal in the end. I'll probably try the bridged-T circuit first and see how it'll work, unless there are better solutions.

enor: Saw that one a while ago. Would be excellent for this organ - if a ready-made kit were available or if I were an electronics engineer. But I'm not :)

Attached a pic of the back of the organ after connecting the Speakon-8 outlet - but before properly fixing the speed switch jack.

[enor]

Wes: I know the difference. The owner could do with a simple volume control, but would prefer a proper expression pedal in the end. I'll probably try the bridged-T circuit first and see how it'll work, unless there are better solutions.

enor: Saw that one a while ago. Would be excellent for this organ - if a ready-made kit were available or if I were an electronics engineer. But I'm not :)

Attached a pic of the back of the organ after connecting the Speakon-8 outlet - but before properly fixing the speed switch jack.

If you can design a voltage-divider type volume circuit, then "my" solution is a walk in the park. It's all pre-fabricated modules... the RC world has lots of neat cheap stuff. The only thing "one off" about it is the linkage which I made on my 3d printer.

[Tim_at_Jonas]

The only pedals I know of that have a pot of a sufficiently high value that they might work are the Ernie Ball 6166 (250k pot) and 6165 (500k pot). As to where to put it, I'd try between the Volume Tablet return (F) and the Tone pot (R40). If you don't like the result, perhaps between the junction of C22/C23 and the junction of R37/E/C24. (In either case, the pedal would be wired in as a standard voltage divider.)

Or change the preamp to a Trek, which uses a pot as the expression control - you could wire in the EB pedal instead.