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KK · Platinum Member Joined: 13 Oct 2016 Posts: 1422

Got my new multimeter a week ago and finally got some time to solve the most disappointing thing about my K2 since I bought it, the aftertouch. Mad

Not only it needed an enormous amount of force simply to reach the initiating threshold, but it also offered a poor pressure control (quite exponential response).

After analyzing the circuit dedicated to aftertouch in my K2, I decided to design a solution to solve this. Note that this mod is designed for my model, which is equipped with a RH3B 88-key keyboard. I have no idea if it will work on other Kronos models.

Also, this solution involves a hardware modification, so it is not for everyone. Shocked

This solution reduces as much as possible the initial amount of pressure needed to initiate the aftertouch and also adds a sub-circuit in the existing twin op-amp circuit in order to give it a more linear response.

This mod is not very complicated when you know how op-amp circuits work, but it involves quite a bit of tests. The result is a notable improvement. The aftertouch now needs less force to start and its response is more linear. Cool

https://vimeo.com/260649165

voip · Platinum Member Joined: 27 Nov 2014 Posts: 3773

If the range of available aftertouch curves doesn't cover requirements, then the built-in aftertouch calibration has sufficient adjustment range not to necessitate any changes in hardware, unless the aftertouch circuitry has developed a fault. The only issue seems to be that the on screen dialogue doesn't make it clear what the user should be doing, and the manual doesn't help.

Making aftertouch too sensitive can result in it being invoked during normal playing.

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KK · Platinum Member Joined: 13 Oct 2016 Posts: 1422

dfahrner · Posted: Mon Mar 19, 2018 2:12 am Post subject:

Lovely video and music, I guess, but where's the schematic? the technical information? ??? ...and I'd have to say that one thing I've learned ftom years of making hardware mods to musical equipment is: never modify the case (the outside) of an instrument if you think that you ever might want to sell it...

df

KK · Platinum Member Joined: 13 Oct 2016 Posts: 1422

I actually totally agree with you about not modifying the outside of musical equipment. But it is of no concern for me though as I don't plan to sell my K2. I usually keep the musical instruments I really like during decades.

Also, despite being rather simple, not everyone can accomplish a mod such as this one safely without damaging their synth, so one must remain careful about providing too much info publicly. Interested people could PM me if they want to know more. About a schematic, as mentioned in my video, components values for the additional sub-circuit depend on tests done on the particular Kronos and will vary according to the FSR under the keys and hardware settings on the existing op-amp circuit. So the only way to complete the new sub-circuit is to first do those tests.

The only technical info actually important for this solution is that to improve aftertouch threshold and response, the existing op-amps need to be operated at a precise setting and since any FSR response can vary with time, temperature, humidity and even between similar components of the same production batch, it is imperative to add an external adjustment potentiometer for the mod. So again I totally understand if people are not interested because they don't want to modify their Kronos appearance. It really depends on how important is aftertouch for the musician. Some almost never use it.

Broadwave · Posted: Mon Mar 19, 2018 8:10 am Post subject:

I have to admit that the aftertouch response on my K2-88 is a bit tough, even after the OS calibration - The K61 that I had before was far better.

Thanks for the info KK, I may just look into this.
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AntonySharmman · Posted: Mon Mar 19, 2018 9:44 am Post subject:

Kronos Fatar aftertouch is using pressure carbon resistor that is applied to the whole keybed and the varying value
is proportional to the sum pressure of all fingers that are applied on keybed so this 1 KΩhm average value that controls
Jfet Operation Amplifier bias , differs between semiweighted and fully weighted keybeds !
I find this mod very usefull for custom sound development where AT has pitch duties especially in custom AT pitch lead
guitars & solo analog lead sounds especially on weighted keybeds but IMO this will disorder the majority of factory sounds
in ordinary semiweighted keybeds.
E.Guitar in this video has been played exclusively with AT pitch https://youtu.be/lyAL9Ozh-9k?t=5m15s

I have modified many times OP-Amp bias in older Fatar normal keybeds , where AT carbon resistor had been "loosen" after
heavy usage and needed out of range re-calibration.

My advice is to use global keybed sensitivity first and before varying any internal adjustment potensiometer , first measure
and write down preset AT bias voltage before alter anything !

Hope this helps
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Keyboards : Steinway-D, Kronos X, Pa5X 76, Pa4X 76, Montage M7 , Roland-XV88, Emu3,Emax II,Synclavier II,Yamaha DX Series, ΟΒ-8V

KK · Platinum Member Joined: 13 Oct 2016 Posts: 1422

KK · Platinum Member Joined: 13 Oct 2016 Posts: 1422

SeedyLee · Posted: Tue Mar 20, 2018 2:48 am Post subject:

AntonySharmman · Posted: Tue Mar 20, 2018 3:15 am Post subject:

DeltaJockey · Posted: Wed Mar 21, 2018 12:14 pm Post subject:

KK · Platinum Member Joined: 13 Oct 2016 Posts: 1422

BlackForest