Yamaha FC-7 expression pedal response problem

[Benjo26]

Hi there,

I recently bought a Yamaha FC-7 expression pedal for use with my Roland RD-800 stage piano. This is essentially a potentiometer on a rack and pinion with a hardwired TRS output.

The problem is that the FC-7's response is very uneven. Within its first 10% of travel, it covers the full range of the assigned variable. This is a known problem relating to the compatibility of the FC-7 with a wide range of keyboard brands. See discussions:

http://forums.rolandclan.com/viewtopic.php?f=38&t=48739
http://forums.rolandclan.com/viewtopic. ... =10#p72827

The solution commonly offered for this problem is to rewire the TRS output swapping ring and tip signals. This polarity swap can be achieved by rewiring the hardwired output or by fashioning some sort of adapter (e.g. http://music.ashbysolutions.com/misc.htm , http://barrysmixedreviews.blogspot.com. ... 7_313.html ).

Not having a soldering iron, and not having been able to find the right y-jacks, I've approached a music tech to make me an adapter like the Ashby Solutions model (link above). But first I'd like to understand why a polarity swap like this would affect the response problem.

My current understanding of polarity in relation to pedals is that it concerns the orientation of the 'full on' and 'full off' positions. But this seems to be a very different sense of the idea.

Could anybody please explain the relevance of the tip and ring signals to the evenness of the FC-7's response?

Thank you!

[justin3am]

The FC-7 uses a 50k log taper pot, where the Roland EV-5 uses a 10k linear taper pot (for the main control element). I imagine that the Roland keyboard is expecting the EV-5 pedal, which would certainly explain the response curve you are encountering with the FC-7. A polarity switch/adapter cable would not change that.

[Benjo26]

The FC-7 uses a 50k log taper pot, where the Roland EV-5 uses a 10k linear taper pot (for the main control element). I imagine that the Roland keyboard is expecting the EV-5 pedal, which would certainly explain the response curve you are encountering with the FC-7. A polarity switch/adapter cable would not change that.

Thanks very much for the quick response.

That seems a very reasonable view. I would call that the end of the matter if it weren't for the confident claims of consumers and advisers that the polarity switch does help with compatibility between the fc-7 and Roland keyboards.

Since you seem to be in the know about the technical side of the issue, I wonder if anythings jumps out at you reading the links above?

Cheers!

[BertKoor]

The polarity swap would work! Then "halfway" the total resistance of the log pot is not at 10% or so from the start, but at 10% of the end. So you get fine control where you need it. But ofcourse 0% and 100% get swapped as well.

I'd just buy a Roland EV5, costs about 35 last time I looked.

[JCJR]

Either roland-type or yamaha-type pedals and keyboards are generally compatible with the rewiring trick.

The potentiometer is used as a voltage divider to deliver a control voltage to the keyboard, and the keyboard reads that voltage to decide the footpedal level, midi value 0 thru 127.

The pot is a resistor with a wiper that can continuously tap the resistor at various points in the control rotation. Used as a voltage divider, one end of the resistor is grounded and the other end connects to +5 volts, or +12 volts, or whatever the keyboard wants to use. Then when you rotate the wiper, if there is 5 volts across the pot, the wiper will go from 0 to 5 volts thru the rotation. If there was 12 volts across the pot, the wiper would go from 0 to 12 volts thru the rotation.

Both the roland style and yamaha style use a Ring-Tip-Sleeve plug on the pedal. Both styles connect the synth ground to the Sleeve of the pedal plug. On one style the voltage from the keyboard connects to the Ring of the plug and the variable voltage out of the pedal goes out the Tip of the plug. On the other style the plug's Ring and Tip are reversed.

So that generally lets the wrong flavor pedal kinda-sorta work, but the taper is all screwed up, because it isn't acting like a voltage divider. The positive voltage is coming in on the wiper, so when the pedal is off, it is shorting the voltage to ground, so obviously the top of the pot goes to 0 volts as well, and the keyboard volume will go toward zero. But then when you raise the pedal, the voltage at the top of the pot rises fast, so it goes from zero to full quite suddenly.

I had to rewire a roland-type pedal to work with my yamaha KX88 keyboard. The symptoms were identical, very sudden change from off to full-on. Depending on keyboard circuit and pedal brand, maybe there could be other symptoms in some cases, dunno.

[Benjo26]

The polarity swap would work!

Either roland-type or yamaha-type pedals and keyboards are generally compatible with the rewiring trick.

Thank you both very much for your posts.

JCJR, that seems like the kind of answer I was looking for. Clearly I've got a bit of electronics reading to do, but it sounds like there's good reason for the trick after all. Thanks very much.

[lfm]

There might be settings of both styles of pedals - the ones with output in tip the other on output on ring.

As well as polarity thingy.

So check settings in Roland what you can tell about expression pedal input.

I know Roland and Korg are different, but don't know about Yamaha pedals.

[JCJR]

Yep as far as I've read, the market is maybe rairly evenly split, with one set of brands doing it one way, and another set of brands doing it the other. Including the various newer low price midi controllers.

Desirable features available in some pedals include a polarity switch, and an offset knob so one can fine-tune the volume when the pedal is at lowest position. I wanted to get one of those when I needed an extra pedal, but at the time I needed one, the models like that were out of stock at online stores that carried them.

Sustain pedal momentary switches can come in two flavors as well, normally off and normally on. Lots of keyboards either have a software setting to change it to match a sustain pedal, or some keyboards automatically sense it when you turn on the keyboard, so that either type "just works".

Many momentary switch pedals have a double pole microswitch inside, making it pretty easy to change polarity if needed, by opening the pedal and resoldering one wire.

[Benjo26]

Had a helpful email from Bruce Wahlberg at Ashby Solutions partially explaining the logic of the fix.

According to him, 'polarity' is a misleading word. It's principally to do with the proper locations on the pot for voltage input and output.

Wouldn't the 'polarity' of the pedal in the sense of on vs off positions be a case of interpretation by the keyboard? Ie 127 / full voltage = 0 volume vs the opposite? But I have noticed pedals with polarity switches, which confuses that theory.

The RD-800 does have a system setting for pedal 'polarity', which governs on/off orientation. It also allows you to set minimum and maximum for any variable assigned to the pedal. This seems more desirable than the hardware low-limiter because of its flexibility.

However unlike e.g. the Nord Stage 2 the RD-800 does not have a system option for specifying the pedal. Perhaps this has to do with Yamaha vs Roland product wars. Or maybe it has to do with other factors relating to the desirability of tip /ring vs ring / tip orientation.

How cool would it be to have keyboard firmware that allowed you not only to select the exp pedal in use, but to custom map the response curve? I wish!

[Benjo26]

Haven't mapped the response curve or anything quite so earnest but can report that the Ashby-style adapter cable made for me by a local amp technician for $25AUD has worked wonders!

[Jim Y]

You did the right thing to keep the FC-7. The Roland EV-5 is cheaper, but for what it is, it's only worth half its price - it's not robust enough for serious use.

[lfm]

You did the right thing to keep the FC-7. The Roland EV-5 is cheaper, but for what it is, it's only worth half its price - it's not robust enough for serious use.

I never had issues with EV-5.
Have four units, and the oldest 15 years old still going as well.

I don't know about Yamaha model is better, maybe it is.

But stating that EV-5 not for serious use - I don't agree.
And the adjustment for limiting range is very good as well.

[Jim Y]

It's not just my opinion, but I went against advice and chose the Roland over the Yamaha anyway because it's a Roland - so it should be decent? The one I have failed within a few weeks - glitchy pot. Maybe they've cut production costs on recent ones and using cheaper components?

It's nice to know that one made 15years ago is still good, but unfortunately that's no measure of how good any made now will be.

Anyway, I've just done a search of FV-7 versus EV-5 and what I've read has done nothing to alter my opinion. Everyone is free to search likewise and draw their own conclusion.

[BertKoor]

The Roland EV-5 is cheaper, but for what it is, it's only worth half its price

Price difference here is not even enough to buy a Big Mac

it's not robust enough for serious use.

I still have the one I bought, ehm lets see... oh 20 years ago at least. Still going strong and withstanding my abuse. Using it every week with band practice to control my main volume. So it's had 20 (years) * 50 (weeks) * 50 (slides) = 50.000 foot movements to endure. Quite a robust thing, didn't really expect that from a plastic case!

[ulph]

I found this thread when troubleshooting wiring a set Roland RPU-3 pedals and a Yamaha FC-7 pedal... to my DYI keyboard controller, so I suppose I'd just wire the jacks specifically

Thanks!