Expression pedal possible issues?

Quad Cortex
1

Greetings,

I hope all is well. I am experiencing some problems with my home brewed expression pedal.

I have an expression pedal that I made that uses a switch to switch the potentiometer in the pedal between two separate TRS cables. One cable is connected to Expression 1 and the other into Expression 2 to control the Gain Block Level and Wah respectively. Now each cable on it’s own works flawlessly to control the Volume or Wah, but the issue lies with the parameter which the pedal controls once the pedal is basically “deactivated” from the respective circuit, i.e. Volume or Wah.

For example, when the Wah is at 100% (pedal all the way toe down) and I click the switch to change the pedal’s function from Wah to Volume, the Wah parameter in the QC does not go completely “off” to 0, but floats slowly to somewhere around .50 of the value.

Same thing with the volume control. When the pedal switches from the “Volume circuit” to the “Wah circuit”, the volume floats down to around -10 db from 0 db (pedal all the way toe down).

Now keep in mind that when the Wah circuit is connected to the potentiometer, the volume circuit, or basically the cable connected to the Expression 1 input is literally just a cable, connected to nothing.

This can be replicated if you just plug in a regular TRS cable in the Expression pedal input and the expression input pedal is connected to a parameter on the QC.

For example, if the gain level is connected to the expression pedal input as a controller, plugging in a regular TRS cable will drop the volume to around -10db, or so. If this could be confirmed, I’d appreciate it.

I understand that there’s some resistance in the cable, but I had an FM3 and this was not an issue with that unit, so I believe that this may be something that could be just a programming issue or something like that with the QC its self.

If anyone could provide some insight regarding this issue that would be great.

Thank you!

2

Hi,

You could probably solve that by putting a resistor to ground when the switch deactivates one of the TRS.
Like the resistor we put on our DP3T switches in analog pedals that pop when switching on or off.

Strymon Tech Corner #1 - Anatomy of an expression pedal ...

(discard about the R2 resistor in the image)

3

Hi Thomas,

Thank you for your reply.

I believe this is exactly what I did literally a few minutes after I had made the post.

I connected a resistor between the tip and the ground of the TRS cable. This makes it so that when I disconnect the TRS cable that is connected to the potentiometer, the value of the parameter that is assigned to Expression 1 goes to 0. So okay, there, we’re good.

For the volume “circuit”, I need the pedal to stay at 0.0 db not at “off”, so I connected a resistor between the tip and the sleeve. This also gives me the satisfactory result of having the volume circuit remain at 0.0 db whenever the circuit is disengaged. Although this is all fine and dandy, I believe that the sweep of the pedal is somehow skewed by adding these resistors.

I recalibrated the pedal, but it seems like most of the action on both of these circuits happens either near the heel or the toe of the pedal sweep, depending on which circuit is engaged (i.e. if the resistor is between the tip and the ground, the sweep is more sensitive near the toe of the pedal, and if the resistor is between the tip and the sleeve, the sweep is more sensitive near the heel of the sweep).

I’m gonna check it out a little more later to see what’s up exactly or if there’s a other place to put the resistor to fix the sweep problem.

However, I played a show with the pedal last night and it worked flawlessly. I would like for the peak of the sweep of the wah to be more around the middle of the sweep of the pedal instead of closer to the toe however. I’ll see what more I can do about that. Any ideas?

For more technical details, read the following:

The resistors I placed in the two circuits are 1k ohm resistors. I tried experimenting with other types of resistors and it seems that with a 1M ohm resistor the values do not go completely to 100 or 0%.

For example, the volume circuit with a 1M ohm resistor between the tip and sleeve sets the gain level to -2.3db whenever the volume circuit is disengaged from the potentiometer. A 4.7M ohm resistor makes it -5.3 db or so. If the tip and the sleeve are disconnected completely, the value is -10.1 db or so. This means that the QC is looking for a specific resistance value between the tip and sleeve to make the gain level be 0.0 db. This may have something to do with the ground not being connected as well. Maybe I should have a common ground between the two circuits and the potentiometer.

Anyway, I believe this means that the resistor I should use to have the least amount of impact on the actual potentiometer whenever the circuit is connected to the potentiometer so that the sweep of the pedal is “balanced”, while still bringing the values of the circuit when disconnected from the potentiometer to the values I want them to be at (i.e. 0.0 db for the volume circuit and “off” for the wah circuit) should a a resistor just shy of 1M ohm. Maybe 750k ohm or so. I’ll buy one and try it out but does anyone know what value the QC expects to see as a resistance/voltage value between the tip and sleeve to set the disconnected circuits to exactly 100% of the value or exactly 0%.

The value of the pot in the pedal is 10k just in case anyone is wondering.

Thanks!

4

Love that stuff !

What about the smallest resistor you can find ?
How would that work ?
1k for a 10k pot is quite large (10%)

I recalibrated the pedal, but it seems like most of the action on both of these circuits happens either near the heel or the toe of the pedal sweep, depending on which circuit is engaged (i.e. if the resistor is between the tip and the ground, the sweep is more sensitive near the toe of the pedal, and if the resistor is between the tip and the sleeve, the sweep is more sensitive near the heel of the sweep).

You are changing the sweep with that resistor (I think it is turning your pot to a log or anti-log vs linear)
Start with tiny resistors ( 1R, 10R, and so on).

5

Hey @Vladi !

Something even more stoopid !

What if Your expression pedal had a pot connected to Expression 1 and the switch connected to Expression 2 ?

With a little tinkering on the QC, the switch would bypass block 1 & turn on block 2 at the same time (toggling) and the pot would control whatever block is on.

… hum hum, I think we just re-invented the wheel : the Mission Engineering expression pedal with a switch… For a couple of dollars/pounds/euros (shows how you can make a huge profit with a 10K pot, a switch and a wah enclosure, some nice paint and hell of a marketing team)

6

My bad, in fact you are turning your pot into a “never at 0” pot or “never at 10k” pot (like a boss FV-50 for ex with an extra pot on the side):
it’s parallel resistors that change the taper.

7

Hi Thomas,

Thanks again for your replies.

Regarding the tiny resistors, I am not sure if that would really work in this case because it seems as if there needs to be some resistance but not too much between the tip and the sleeve for the QC to register 0.0 db on the gain level parameter whenever the TRS cable is disconnected from the circuit.

For example, if the tip and the sleeve are disconnected, there is “infinite” resistance, and therefore, the gain level parameter goes to -10.1 db. I didn’t look to see the actual value in the expression pedal input settings on the QC, but I believe it’s somewhere around 50% whenever the TRS cable is disconnected from the pot.

If I jump the tip and sleeve soldering lugs, the gain level parameter jumps to 0.0db, which is good. But most likely what is happening is that the QC is reading a voltage value MUCH higher than what is normal to give 0.0 db on the gain level parameter, but because 0.0 db is the maximum limit, it displays 0.0 db. I hope that makes sense.

When I put a 1M ohm resistor between the tip and sleeve, I get a -2.3 db value on the gain level parameter. This means that a 1M ohm resistor is providing a bit too much resistance. This is confirmed by the fact that if I put a 4.7M ohm resistor, the value of the gain level parameter drops to -5.3 db.

This means that if I put a resistor that is just slightly under 1M, I should get the QC to show me exactly 0.0 db, without going much over the value that is supposed to give 0.0 db.

Now the issue is that when the pot is connected to the TRS cable, the resistor is also connected to the pot, basically in parallel with the input and output lugs of the pot. This is where I think you’re right. Because the resistor is in the circuit, it is somehow changing the sweep of the pot, possibly.

Does anyone with an actual mission engineering pedal with a toe switch experience this same problem?!

If the mission engineering pedal is basically a switch, switching between two TRS cables, then the results should be the same or similar as I am experiencing with my pedal because the mission engineering pedal and my pedal should be the exact same thing!

Thanks again.

8

You know what, this might work. I think, I could have the switch be inverted on the Wah, and normal on the Volume, and when the switch is disengaged on the volume (disconnected basically), it turns the Wah on, and therefore the pedal controls the Wah. When the switch is engaged (on), the Wah turns off, and then the Volume block will be on, and therefore the pedal will then control the Gain Level parameter.

This actually would solve the problem of the weird sweep on the pedal, as well as give a few other benefits, which would be that now, when the switch is pressed, the Wah will turn off automatically, and I won’t have to worry about the heel-toe switch delay. This would be very nice as it would perform just like a Wah pedal. When it’s off, it’s off. No waiting, no weird fast sweeps to the heel position when the pedal is deactivated ( this is because I set it to go off in the heel position so it doesn’t go off automatically in the toe position where I use it most) and lastly, no turning off when in the heel position but I am still using the pedal.

The third added benefit is that I would be able to see, visually on the QC which blocks are active, therefore telling me if my pedal is in Wah or Volume mode.

I have some stuff to do right now, but I when I get back tonight, the pedal will be taken apart and rerouted to achieve above stated (honestly, I think this is how the Mission Engineering pedal works too, which would make sense. Looking at the manual right now, it looks like this is exactly how it works).

Thank you for your insight Thomas. Always great to talk to people about these things. All the best!

9

I actually think the mission pedal is what I described here : a pot to Expression 1 and a switch to Expression 2

The switch toggles Blocks (like wah and whammy)

You would need to go to your wah block > assign expression pedal 2 (switch) > bypass
Same thing but inverted for the gain block

Click the switch Wah is on and volume block is bypassed
Click again Volume block is on and wah is off

Then assign the pot (expression 1) to those blocks as Gain and Wah

No need for resistors in this case

10

Yup. That’s what I will do tonight. I’ll post my results once I have everything reconnected. Thanks again Thomas, and yes, the Mission Engineering pedal, per their Manual, has one output connected to the pot and the other to a switch.

11

ALRIGHT!

After some de-soldering, soldering, some more de-soldering and some more soldering, I have the pedal working with output 1 of the pedal connected to the pot, and output 2 connected to the switch, and the switching of the pedal between the Wah and Gain block works so well. I am very happy with this change. I feel the pedal, and it’s connection to the QC, is much more robust.

I am still having problems with the sweep of the pedal being too far forward however. For the volume, it’s okay, but for the Wah, the “WAH” part of the sound happens very much at the toe end of the sweep. It would have been a lot better if it was somewhere closer to the middle, or at least like 2/3rds of the way up the pedal’s sweep.

When I am doing the calibration, basically half of the pedal’s sweep is unregistered. The second half is what is actually being registered. So basically, only when I travel past halfway of the pedal’s sweep does the calibration meter on the QC start to move from 1.00 down to 0. Weird, huh?

If anyone could provide some feedback on this issue that would be great. My idea is to put a resistor in the sleeve or the tip cable going to the pot to increase the pot’s resistance (the pot is a 10k linear pot) and therefore hopefully push the pot’s sweep further back in it’s path of travel.

Cheers and thanks for your idea Thomas! Great insight.

12

What if you adjusted the pot gear so that your 100% on the pedal was less than the pot’s 100% ? (I had to do this on my hacked Boss volume pedal turned into an expression pedal)
Then recalibrate…

13

Hi Thomas,

Thanks again for your reply.

I discovered what the problem was. I had soldered the sleeve, instead of the tip, to the wiper of the pot. Switching the two wires around solved the pedal sweep problem completely. The pedal is functioning excellently. The volume swells are lush and the wah is functioning perfectly. I am very happy that it was an easy fix.

Thanks again for all your replies!

14

:partying_face:

Now it’s wah and volume party time !

15

Oh yeah!

I did realize however that I connected the switch wrong too…I connected the TRS cable to the center lugs, and then jumped the ground and tip on one side of the switch, and on the other side, I jumped the tip and sleeve. This was giving me a gradual decrease from 100 to 0 whenever the switch was engaged/disengaged. While this does work, I now realized that I could just connect the tip to common, and the ground on one side and the sleeve to the other side. This will eliminate the gradual decrease from 100 to 0 and make the switch transition instantaneous from 0 to 100 and vice versa.

There you go, pedal perfected!

16

Guys, I have the Dunlop Petrucci signature and it is not able to add in Expression inputs and calibrate it.

It is only working adding my guitar in the input of pedal and the out of pedal in the input of QC.

How is the correct way to use with this pedal?

Tks a lot

17

That’s a wah pedal, my guy. You need an expression pedal for it to work like you want it to work.

1 Like
18

There are some volume pedals that will do double duty as expression pedals. I used to have an Ernie Ball volume pedal that worked as an expression pedal, but Wah pedals aren’t so easily substituted. As @Vladi pointed out, the QC is expecting to be calibrating an expression pedal, not a Wah.

Since Wah pedals are usually at the front of a signal chain you could continue putting one in front of the QC if you wish although you might prefer the options of the QC’s onboard Wahs with an expression pedal.

19

Guys, I can’t calibrate my Dunlop DVP 3. I’m using TRS cable, but when I connected to EXP1 or 2, the gauge goes to 100 and do not move anymore. Any help? tks

20

If you search the forum on “Dunlop DVP” It looks like there are a few other users on the forum who have been successfully using the Dunlop DVP 3. Might want to try contacting one of them directly on the forum.

One thing I would try is swapping out the cable to make sure it is not the issue. Cable as you noted should be TRS. Make sure you are coming out of the ‘EXP’ jack on the Dunlop. Here are some instructions from the Dunlop’s manual that may or may not help depending on whether the issue is on the pedal or the QC side. You will have to combine these instructions with the calibration process on the QC.

From the Dunlop DVP 3 manual:

EXPRESSION MODE (10 kΩ POT)
• Run a stereo or TRS cable from the
Volume (X)’s FX jack to your effects
pedal’s expression jack.
• With the pedal in full toe-down
position, set the effect parameter
you want to control to the desired
maximum level.
• Optional: To set the effect
parameter’s minimum level, use
internal potentiometer toward
the front of the pedal. Turn it
clockwise to raise the minimum
level or counterclockwise to lower
it. Note: factory setting is fully
counterclockwise.
• Move the rocker pedal toward the
heel-down position to lower the
value of the effect parameter within
the range set by your effect pedal’s
control and the Volume (X)’s internal
potentiometer.
• When the rocker is fully heel-down,
the effect parameter will be at
the minimum value as set by the
internal potentiometer.
• Optional: Use the internal blue push
switch to reverse the function of
heel-and toe-down postions.

1 Like