Korg FK-2 Mr. Multi vero.

[digi2t]

Hey boys and girls,

I've been at it again. Recently discovered this pedal on Ebay. In the 20 minutes it took me to research and fall in love with it, it was gone.... DOAH!!!! So, did the next best thing;



a bit smaller, but with BOM;



and the switches and pot wiring; Wah - Phase - Double switch (note the added resistors)



Pedal - Auto switch, and treadle pot (note the added resistors and tantalum capacitor)



and the complete schem. I had to make a small correction to 3 resistors, as per the PCB trace and component layout. Both below;





Sorry about the crappy resolution on the vero pics, but I had a no go uploading to Photobucket tonight. Freekin' javascript void error. Always something...
As for the IC's, I think an LM358 and an LM324 might work in here. The JFET's are still fairly available, but you could always socket and play with it. C20 says 33uF, but I think it's a 100uf. This is just the map, drive your own car  

Well, time for some shut-eye. Going to trace this puppy tomorrow, and see if she passes the first test.

Cheers,
Dino

[digi2t]

Updated the vero. After careful examination of some gutshots, it was missing a couple of caps, and I had to move some stuff around.

C20, the filter cap, doesn't show on the schematic, or the hand drawing. But, it is indicated on the PCB layout as a 33uF. Looking at the picture, it's way bigger than that, maybe a 100uF (bottom, center of board).



There's only one other 33uF cap (left side, beside the trimmer), so you be the judge. In any case 100uf is pretty standard here.

[digi2t]

Updated vero (again), with updated schematic. Disregard the previous schematic. Retraced the PCB, and found that there was some discrepancies on the schematic. This should be the final version, but if anyone spots anything, let me know, so I can put things right. I've been working with grainy pictures, and a lot of zooming was involved, but I believe this to be correct. I added two off board resistors to the board, to make things a bit more tidy. The switch wiring should be as per schematic. The diodes might be tricky. There are 3 1S1555's and a 02BZ4 Zener. The Zener is throwing me a bit, since the schematic states 3.5v, but the 02BZ4 is a 4.7v Zener. I'm assuming that it means that the trimmer should be adjusted to give a bias voltage of 3.5v. If that's the case, then a 4.7v Zener should be here then, i.e. 1N750, or similar. 1N4148's should be OK here.

If you have any doubts as to the latest version, look in the gallery. I always update there, look under "Dino's Stuff".







I'm hoping to build this soon, but if you beat me to it, drop me a line... or a clip.... or a video.  

[Skruffyhound]

You are a fast worker mate, well done. I have no time right now and I don't do vero normally, but even I'm tempted. Love to hear it when you get it going. Those 2SK30A's are a bit expensive to get enough to match IIRC, they are in the Boss slow gear too. I got mine working with some old Fets from an eighties stereo but later bought some to see the difference.
Banzai has them here for €0.30
http://www.banzaimusic.com/Other-Transistors/
Compared to a 2N3904 at €0.05
I know you are in the States, but just for comparison.
I'm guessing they are not easy to sub for something else.

[Skruffyhound]

Nice

[digi2t]

Thanks man. I always socket everything, but I did buy some 2SK30A's. I'll try some other  fets as well, and see what works best. On the flip-side, I'm going to try LM358 and an LM324 for the IC's. I also have TL072 and TL074 on hand, so I'm not going to get any of the spec'd chips just yet. Besides, I've found the original chips online. but pretty pricey .

Skruff, can you do me a favor? Take a look at the schematic, and the PCB layout for me. Just verify the area where the 3 diodes are. The original schematic, and hand drawings (found on the net) had CP10 joining above the 3 diodes, and then going on to the wiper of the 10K trimmer. To my eyes, this is wrong. I see CP10 joining between the first and second diodes (from the top), and the wiper of the trimmer connecting above the diodes.





Appreciate it.

[Skruffyhound]

Man, actually had to put my glasses on. After a few minutes of squinting though ... looks right to me, if what you are asking is are the layout and the schem the same. CP10 (marked GN 10 on the layout) joins above the three diodes and the wiper of the trim joins between diode 1 and 2 counting from top. Would it be possible to upload the layout with the contrast screwed up higher and the schem enlarged with a vector prog like inkscape. The schem I could do myself, but if you are keeping all this together in your gallery it's neater if you upload it. I'd like to have another look at it when I can...er see it.

[Skruffyhound]

About the 33uF cap, it could easily be a 33uF at a higher voltage rating, shouldn't matter much though if it's just between the rails

[digi2t]

Man, actually had to put my glasses on. After a few minutes of squinting though ... looks right to me, if what you are asking is are the layout and the schem the same. CP10 (marked GN 10 on the layout) joins above the three diodes and the wiper of the trim joins between diode 1 and 2 counting from top. Would it be possible to upload the layout with the contrast screwed up higher and the schem enlarged with a vector prog like inkscape. The schem I could do myself, but if you are keeping all this together in your gallery it's neater if you upload it. I'd like to have another look at it when I can...er see it.

Evrything is in the gallery, under "Dino's stuff/veros". There's also a PCB transfer, which I think is correct. If you invert it vertically, you get the equivilent of the pale layout, minus the component markings. I'll see what I can do for the contrast. I think I can give you a larger schem through Imageshack. Might be really big, but you could always tape it together in sections. Give me a bit, I'll get you that.

I'm pretty sure it's a 33u cap by the diode, but in the gutshot, the filter cap looks huge compared to the others. But, I figure it must be a 100u here. that's what I put on the vero.

Back in a bit....

[Skruffyhound]

Cool. Yeah I was just saying that the bigger the voltage rating the bigger the cap, so, a 33uF 10v and a 33uF 100v for example, will be different sizes but still 33uF. Size of caps can be misleading. Anyway, the 100uF should be fine.
See you later.

[digi2t]

OK, how's this...









PCB transfer image hasn't been verified.

[Skruffyhound]

Better thanks.
Well I can't see anything wrong with that section. I haven't checked the rest but from 10 and 11 through diodes/trim and over to that 1k5, the 470k to ground, the 8k2's to ground, everything checks out with the schem. The trim was bothering me until I went back and checked out the guts but thats right too.
10 is before all diodes,trim wiper after the first before the second.
Now you've just got to build it so we can hear it and the modding can begin 

[nickbungus]

Right.  I've been struggling to get my fOXX Phaser pcb layout down to a manageable size and have jumpers everywhere.  I've got models in Eagle, DesignSpark and DIY Layout Creator, but cant get it nailed. 

So I thought to give me a break I'd build this. As digi2T pointed out to me, they are very similar.  I may even mod it a bit to bump the phaser up to 6 stages.

I can't source any 2sk30a gr trannies and because of the matching, I'll need a few of whatever I go for.  Has anyone had any joy with anything else?  I'm no electronics engineer so I'm very confused as what to use.  I was thinking of J111s?  Does anyone recommend anything?

Also, is the PCB transfer ok?  I don't enjoy Vero.

Thanks

[duck_arse]

digit - wot about using k30a - Y instead of GR ? I sees youse gots a trimmer for the bias, the k30a 's I got from futurlec were "Y", they were quite close for Vgs's, and show as 21 of our puny australian cents each.

even I could afford that. the wait was another matter.

[nickbungus]

That raises a good question, for phasers, and especially this build, when substituting transistors, what are the key properties to match on?  When you look at a datasheet, there are so many properties and numbers etc., it seems almost impossible to get an exact match.

A lot of these trannies are out of production on these vintage pedals. 

[duck_arse]

#1 - what you've got
#2 - what you can get
#3 - what you can afford
#4 - what you can get to work
#5 - what it says on the original circuit.

possibly #4 should be higher ranked.

[digi2t]

digit - wot about using k30a - Y instead of GR ? I sees youse gots a trimmer for the bias, the k30a 's I got from futurlec were "Y", they were quite close for Vgs's, and show as 21 of our puny australian cents each.

even I could afford that. the wait was another matter.

Hey duck, sorry for the delay in replying.

Looking at the datasheet, I can see that there is some intersection between the Y and GR grades. Personally, following RG's paper on jfet matching, I think matching will be the key, regardless of whether you use Y's or GR's. I believe that it should work fine if you match them, and then you can adjust the bias. I even think that 2N5457 might work OK here.

When I built mine, I initially threw the jfets in randomly. I really wasn't impressed with the sound, and compared to samples I heard on the net, I figured something was wrong. It was researching the problem that I ran into RG's article. Setting up the test rig on the breadboard, and testing what I initially used, showed that my choice of jfets was all over the map. After going through my stash, and choosing a tight group, the difference was night and day.

[Spook Strickland]

The schematic link seems to be dead, does anyone still have a copy?

Thanks

[digi2t]

The schematic link seems to be dead, does anyone still have a copy?

Thanks

I have everything here;

http://www.aronnelson.com/gallery/main.php/v/digi2t/veros/Korg+FK-2/

[Spook Strickland]

The schematic link seems to be dead, does anyone still have a copy?

Thanks

I have everything here;

http://www.aronnelson.com/gallery/main.php/v/digi2t/veros/Korg+FK-2/

Thanks so much Digi2t, this is great!