Poorly implemented EXP-2 expression pedal - CV control

[.Jens]

Wow, looks really like the ultimate swiss army knife among the expression pedals. Thx for the link!

[danatkorg]

I have the correct cable, it came in the box. I have owned a Korg T-1, an N1, a Triton Le and now I own a Krome. Everyone of the keyboards with the EXP-2 have had this same response (or similar). The reason I posted on the Kronos forum is because I knew I would get better responses than on the Krome forum. This pedal may indeed work correctly with the Kronos. I can assure you it does not work very well at all with all of the keyboards listed above and I just bought both the Krome and the EXP-2 pedal, both are brand new. I am using the supplied orange cable. There is no way the middle of the throw is 60 - 68 not even close (I used the sequencer to check with many tests) and I am of course plugging it into the correct jack, it doesn't even work with the other jacks. It definately does not work properly and I am sure the Korg guy who answered this post can verify this easily. I believe you if you say it works with the Kronos but it does not with the Krome (or the other keyboards I mentioned). 1/2 way up is about 115 and then it goes to 127 by 70% up

Mr. Korg guy can you please do some tests and report back here about the EXP-2 and the Krome?

I'm assuming that's directed at me. However, I'm at Korg R&D in California; we've worked on the OASYS and KRONOS, but I have't been involved with the Krome, and do not have one here to test. As before, I really think it would be useful for you to contact your Korg Distributor for support; see the link in my signature. They should be able to help you quickly and easily.

[seapea]

This discussion made me get to the bottom of what was going on with my EXP-2, which has caused me grief for a number of years. Like the OP, , nothing much happened over the final half of the travel. So I bought a couple of Yamaha FC7s, which are brilliant.

Back to Using output 2, I got min max readings of 1 to 127. Central travel got a reading of 110. That identifies what is happeneing.
So I opened it up, and found that output 2 was connected to a 90K LOG pot, and the audio path to output 1, had a linear 50 k pot.
As we all know, volume pots in an analogue audio path should be log.
I swapped the 2 pots around, linear 50K for expression, log 90K for analogue volume. Now it works fine with 65 mid position reading as expected.
[quote

=".Jens"]Just to state a few facts, to whom it may concern:

My EXP-2, which I bought new stock and never changed anything of the inner parts, has two pots (or more precisely a double layer pot, I think - I did not open it this time):
- One 50k linear pot for the audio signal path (IN-OUT1), which always reads 50kOhms on the IN jack, and ranging from 0k to about 47k over the pedal throw, middle position 26k (it's a bit difficult to find the exact half) - so: linear.
- The expression part (OUT 2) has a 90k linear pot, where tip (3) and sleeve (1) are the outer contacts (reading a constant 90k between those two), and the sliding contact goes to the ring (2). Again, middle position is about 47k.

At the end, here's a list of expression values, taken from http://acapella.harmony-central.com/sho ... Pot-Values :

Bespeco VM18L - 20k
Boss FV-500 - 10k linear (expression pot)
Boss EV-5 - 10k linear
Boss EV-7 - 10k linear ("extra range" pot adds up to 50k ohms)
Boss FV-50L - 50k linear
Ernie Ball VP jr. (active) - 25k log
Ernie Ball VP jr. (passive) - 250k log
Korg EXP-2 - 50k linear

Jens, your pedal has a 90K linear pot , as shown by your measurements, that is why yours works. Mine has 90K log.
But I also noticed in your HARMONY CENTRAL list that it says EXP 2 is 50 K linear.

So looks like some variations on components. But simple solution, make sure the linear pot goes to output 2, and log to the audio path. Or if you got 2 linears, then your audio path will have issues when using the pedal. So thanks for topic being discussed, I now have a normal operation EXp_2 pedal

[.Jens]

As we all know, volume pots in an analogue audio path should be log.

That's right in general, as an exponential increase in electric signal level (which can be achieved with a log voltag divider) matches a more or less linear increase of perceived volume or "loudness".

However, especially for volume pedals it depends what kind of signal you want to manipulate and on the context - if you want to have sensitive control over the onset of distortion of a tube overdrive (e.g. Hammond clone into a leslie), it is sometimes better to have a linear pot, as this gives you a finer resolution in the upper range.

If one prefers lin or log in the audio path, is a matter of taste somehow, and this is why there are both kinds of pots available for analog pass-through volume pedals. I have had both kinds, and like them both for different applications.

[roger2600]

I checked the K-ohm values of my EXP-2 jacks and it appears that the two pots are solderd to the wrong jacks. Unbelievable!

Korg where is the QC department?

[danatkorg]

I checked the K-ohm values of my EXP-2 jacks and it appears that the two pots are solderd to the wrong jacks. Unbelievable!

Korg where is the QC department?

If the pedal is in fact wired incorrectly, I'm sure that Korg can solve the problem for you - but I'd suggest talking to your Korg support department before making any assumptions (see the link in my signature). Hardware problems are always possible, but most of the time when someone initially thinks that something very basic is wrong, it turns out to have been a misunderstanding.

[roger2600]

Danatkorg: You may be right perhaps the pedal is built to the correct specifications. I was assuming the guys in the forum are right. You say you do not have a Krome to test but you should know what the CV pedal of a Kronos is supposed to accept. Is it 50K linear? 90K linear? 90K Log? is that what a Kronos is supposed to have as input? Also I'm sure since you work with the Kronos that lists EXP-2 as an optional accessory, you know what the output of these pedals are supposed to be. If you could answer these questions we will finally get to the bottom of the matter.

My pedal has 50K linear on the volume side (the slider adds 50K to it when all the way up to 10), and 90K Log (I think log, it seems not linear) on the output2 - ring - tip
I do not understand what the sleeve is for on outpu2 ??? Can you clarify these things?

Thanks!!!!!

[seapea]

but most of the time when someone initially thinks that something very basic is wrong, it turns out to have been a misunderstanding.

Dan I refer you to my findings above. I trained as an electronics tech and know the difference between log + linear pot. My findings are self explanetry. A foot pedal is hardly a complicated bit of equipment to fault find.
My footpedal had a 90K log pot going to output 2 for expression pedal. .Jens clearly had a 90k linear pot going to expression pedal. Having this pedal for maybe 8 years, I have read enough from people having not much happening in the second half of travel of pedal (like I had), to know that it is likely that there was a batch of pedals that came out like mine. Jens and my experience show these 2 differently wired pedals exist. In the past I couldnt be bothered sorting it out, and just put it to one side, and bought a Yamaha FC7. But I had seen this topic come up so often, I decided to check out what was going on, and sorted it. Cheers

[danatkorg]

I appreciate your comments, but my suggestion is unchanged: contact your Korg distributor.

but most of the time when someone initially thinks that something very basic is wrong, it turns out to have been a misunderstanding.

Dan I refer you to my findings above. I trained as an electronics tech and know the difference between log + linear pot. My findings are self explanetry. A foot pedal is hardly a complicated bit of equipment to fault find.

[.Jens]

I do not understand what the sleeve is for on outpu2 ??? Can you clarify these things?

The way expression pedals (unlike older "CV" pedals) work, is to act as an external voltage divider. A fixed (reference) voltage is applied between the outer pins of the pot (in this case sleeve and tip), and on the slider you will measure a voltage depending on the pedal's position.

So in short words: sleeve = ground, tip = reference voltage (from synth), ring = variable voltage ("to" synth).

This way has the advantage over many other possible implementations, that there is practically no calibration necessary, and that a wide range of pots will work out with whatever synth - you don't have to care if it's 10K, 50K or 100K, you don't have to care what voltage is used - and even lin or log will "just" change the curve of the pedal, not it's range.

[roger2600]

If that is true than why does my EXP-2 not work on the Krome. I get 90K (I think Log) on the output 2. When the pedal is 1/2 way thrown I get 115 to 120 and before 70% it is 127. Actually it is probably even worse than that. Also I am confused why it would work O.K. on a Kronos and not a Krome(if that's really true). Korg has been using the same pedal since the M-1. How is it possible that it doesn't work? Or work differently from one keyboard to the other within their own company?

I am returning the EXP-2 and getting a yamaha FC7, hopefully that will work better with the Krome (sad if it does).

Also I did as Danatkorg suggested, twice, I emailed my Korg distributor. It's been a long time especially since the first time I emailed them (which was before i started this thread) and nothing (I only got the automated response that they got the message and nothing else. [By the way I also wrote to them a long time ago to tell them that the specifications were listed wrong on the website for the Krome, they fixed what was wrong but never answered my email and acknowledged the mistake to me, no big deal of course but why not just answer me.]
Also, I am curious why danatkorg refuses to answer simple technical questions like what is the proper ohm readings for an exp-2 pedal, is he afraid of retribution from korg or does he not know. I understand that he doesn't have to be on this forum but of couse we all know it is for Korg PR and the company wants him here protecting the Korg brand. If he is in R&D and helps design the thing I would think he would know exactly what the keyboard is intended to recieve to make it go from 0 to 127 properly. I don't get why Korg wont answer my question either. What is everybody so darn afraid of? I just want to know what the proper potentiometer is to make the thing work right. I don't get it. The problem is that if I return the EXP-2 because it "doesn't work" than get another one, will it be exactly the same (probably). So the real answer is that the EXP-2 (and the XVP-10) don't even work with the Krome even though it is listed as an acceassory and they have been using the same pedal forever. How can they be that messed up?

[danatkorg]

Also I did as Danatkorg suggested, twice, I emailed my Korg distributor. It's been a long time especially since the first time I emailed them (which was before i started this thread) and nothing (I only got the automated response that they got the message and nothing else. [By the way I also wrote to them a long time ago to tell them that the specifications were listed wrong on the website for the Krome, they fixed what was wrong but never answered my email and acknowledged the mistake to me, no big deal of course but why not just answer me.]

What email address did you use? I'd like to follow up on that.
(In general, it usually turns out that support did respond, but the response got caught in a spam filter etc. Perhaps that happened in this case, perhaps not.)

Also, I am curious why danatkorg refuses to answer simple technical questions like what is the proper ohm readings for an exp-2 pedal, is he afraid of retribution from korg or does he not know.

I answer questions that I know about. I'm not a hardware engineer, and this forum is NOT an official forum for product support. When I think that there might be an issue which could best be solved by talking to the appropriate support folks, I point people in that direction. Anything regarding possible hardware problems, or complex configuration issues, falls into that category. Rather than spending days posting back and forth on a forum, it's often possible to just pick up a phone, talk to someone in support, and get the problem solved in a few minutes - so you're back on track and making music again much more quickly. Not always, perhaps, but most of the time.

- Dan

[.Jens]

If that is true than why does my EXP-2 not work on the Krome. I get 90K (I think Log) on the output 2. When the pedal is 1/2 way thrown I get 115 to 120 and before 70% it is 127.

What does it say when fully retracted ("toes up")? And - is it possible for you to measure the resistance values at the jack that goes into the Krome with a multimeter at the extremes and middle position? That would at least clarify if the pedal has the right values - if possible, just measure the resistances between tip-ring, ring-sleeve, tip-sleeve at the three positions.

Anyway, the topic gave me no rest, and I opened my pedal again to look at the details. First of all, there is a tandem (two layer) pot built into the EXP-2, so it seems strange to me that someone said earlier in this thread that he exchanged just the expression pot - this is not really possible.

Second, FYI, the pot is turned clockwise when the pedal is depressed, the angle is about 240°.

Third, but most important: I don't believe in the log pot hypothesis anymore. The problem is, that usual (positive) log pots, used for audio control deliver around 1/4 of their resistance value when turned to half angle - which makes perfect sense for logarithmic audio control. But if one would accidentally swap a lin pot with such a log pot, the behaviour of the pedal would be nonlinear - but exactly the other way round: it would respond very little in the low end, and very steep in the upper range.

Of course you can even get reverse tapered log pots, but they are quite hard to find, so that is highly improbable to explain so many cases in which the pedal doesn't work.

At least it is certainly not sufficient to conclude the type of pot being used from midi values - there are more possible explanations to these readings than a wrong pot.

So, if there is a manufacturing mistake somewhere, I'd stick to my suggestion to try a crossover cable. The inner workings of the pedal look very much like manual work assembly, so there is a certain chance that two wires are swapped.

[seapea]

[.

First of all, there is a tandem (two layer) pot built into the EXP-2, so it seems strange to me that someone said earlier in this thread that he exchanged just the expression pot - this is not really possible.

: I don't believe in the log pot hypothesis anymore. The problem is, that usual (positive) log pots, used for audio control deliver around 1/4 of their resistance value when turned to half angle -


.

Jens, I think you refer to my 2 posts. Please read my posts with understanding. I said I swapped the 2 pots around. A tandem pot consists of 2 pots. The midi cc values I described tell the story, (before and after mod) and now my pedal operates just like yours looking at the cc values you gave, open, middle, shut. Or if you like like a Yamaha FC7.

I think if a simple problem like this cannot be sorted in the first few posts, then I have to agree with Danatkorg, a forum is not the place to sort the issue. All I ask is you reread my related experience and analyse it logically

[.Jens]

Jens, I think you refer to my 2 posts. Please read my posts with understanding. I said I swapped the 2 pots around. A tandem pot consists of 2 pots.

I was actually not specifically referring to your post - there was another guy, maybe in one of the other threads on this topic, nevermind.

If you just swappes the pots around, then I am really wondering what happened to the audio path - did you try that? Because there is physically no way that a log pot, which is tapered in a fashion that matches your description, would now (after the swap) work as it should on the audio path. It would give the same response on the audio in-out section as it did before on the expression jack, on electrical signal level. The perceived nonlinearity would be even worse.

To make this clear: I do not doubt any of your words - I am just more and more confused the longer I think about it.

The midi cc values I described tell the story, (before and after mod) and now my pedal operates just like yours looking at the cc values you gave, open, middle, shut.

Sorry about the nitpicking, but as I said before, the midi values can only tell that there is something wrong or right - they give no final clue to the cause. There are a few simple ways to reproduce an "inverse log" behaviour like you described it, other than actually having a log pot. A parallel resistor and swapped wires are only two of them.

But that's academic, as long as it now works for you. But I would be still interested if your pedal now still works correctly in the audio path. If so, the only logical conclusion would be, that by swapping and re-soldering the pots you also corrected the wiring of the expression pot - intentionally or not

After looking into the pedal the first time since years again, the most likely explanation for all the reported faults is a bad QC in the production and errors in the (presumably) manual soldering in the factory. Especially as (at least in mine) the sleeve wire is white (and therefore not likely to misplace), while the other two wires are gray and "darker gray".

However, I agree with you, that the OP should now have all necessary info to solve the problem...