Korg Mr. Multi clone build.

[pinkjimiphoton]

sorry dino, out of commission here, got the puter plugged into the gen and modem...not enough lite to mess with trying to see the pedal..couple days.

it sounds ALOT better tho!

yah, you did have phase/double wah switched, huh? sounds a lot better now....well...the same...i mean...ummm...lol...

the double wah sounds like mine now. well done. nice ay yi yi yi yi yi..

hopefully can get to mine soon bro...stay tuned!

[Ronan]

Dino, the PCB is remarkably small! My etching job is a bit rough but good enough. Wondering whether to build it into an auto phase/wah stompbox without the treadle. How about Faze, Waze and Daze for the 3 switch positions?

Here's an insight into the role of the caps at the JFETS. Looks like AC feedback, and the value of the cap may have some bearing on which range of frequencies get the "linearity" applied. Not sure about this though. Thus the 3.5V zener's function is explained. I wonder if 2 series LED's 1.8V x 2 = 3.6V would work well? Just a thought.

Hope you're OK there Jimi...

[deadastronaut]

@ronan: yep! i'd like it in a normal stomp too...no treadle..i really like the phaser.......good work guys...

would that fit in a 1590b?.....and stiick an lfo led indicator on it....

[Ronan]

PCB is about 2" x 2 and 13/16". An LFO LED indicator would be a nice touch for a non-treadle application for sure. My PCB is slightly bigger than that since I left a small border around the outside of the copper.

[Ronan]

Unfortunately my PCB is a mirror image, oops! Will delete the image in my post four posts above. My fault, the photo of the real PCB in the pedal tells the true story. Not to worry. The photo of the underside of the PCB in the Mr Multi vero thread is a mirror image of the real thing and I confused myself I, err, uh-hum, made triple sure my PCB would look like that image um, ahh...but something good came from my mistake, I discovered there is one pad missing that connects a capacitor from pin 1 of the dual IC to pin 12 of the 14 pin IC, it is no big deal though since there is already copper there so a hole can be drilled to do the job. By the way Dino, the PCB does look really nice in the flesh and the track widths and pad sizes are spot on, dunno how you do it! And some ceramic caps just arrived to try out in the EH talking pedal...will let you know the result.

[pinkjimiphoton]

ooooops! at least you didn't forget to plug in your guitar like i have in the past..

[digi2t]

By the way Dino, the PCB does look really nice in the flesh and the track widths and pad sizes are spot on, dunno how you do it!

Sorry man, I can't take credit for that. That's the way I found it off the net. The only thing was that I made a correction to it, because one of the traces was wrong. Didi that with MS Paint. I discovered this when I was using the PCB to cross verify between the schematic, and my vero. When I'm designing a vero, I always prefer to have the schematic, AND the PCB to reference. Pictures are a bonus.

I always try to cross reference all the information I find. It's a PITA to trace and retrace 10 or 20 times, but it really saves on the troubleshooting in the end.

I'm really glad that it works for you. It's always nice to hear that something I can put out here, can help someone out. If there's anything else, don't be shy. 

[digi2t]

@ Ian (Ronan); I found a good description of what's going on with the jfets, caps, resistors by Mark Hammer here; http://www.diystompboxes.com/smfforum/index.php?topic=56187.0 , about half way down. I personally have never used an LED as a zener, I have no idea if that would work. I'm assuming it's current capacity would come into play as well? Since my electronics expertise is technically well below a lot of people here, I tend to stick with "what is meant to be used where"   If it says "zener", then I'm using a zener by dang it.

OK, more serious business... matching the jfet's makes a big difference.

I thought mine sounded pretty good, but matching the jfet's, as per R.G.'s article, REALLY cleans up the phase. In pedal mode, if I swept slowly through it, I could hear 4 discernable "steps" in the frequency changes. Now, it's silky smooth. Article is here; http://www.geofex.com/article_folders/fetmatch/fetmatch.htm . Quick and easy setup on the breadboard.

I highly recommend matching your jfet's if you're building this pedal. I used the 2SK30GR's, as per the original. The 20 that I ordered ranged between 1.657v to 2.015v. The ones I had plunked in before matching, ranged from 1.797v to 1.970v. I measured 5 within the 1.944 to 1.970 range, and used those. WOW... huge difference to my ears. No more stepping through the phase. Whatever jfet's you decide to use, order a good quantity to be sure that you get a good group.

In the mod department, here's one I'm implementing. Not satisfied the depth of the frequency sweep of the pedal in AUTO mode, I've done the following mod to the LFO portion. I replaced the 100K resistor that bridges the opamp inverting (+) input to the output, with a 100K linear pot. Poles 1 and 3 of the pot connect to where the 100K resistor was, and I placed a 10K trimmer between poles 2 and 3. The pot take me from the original 100K depth and speed, and as I dial it down, it increases the depth of the sweep, but consequently reducing the speed as well. The 10K trimmer is to set the maximum depth of sweep. You can go pretty deep (uselessly deep), but like I said, it also slows the rate down as well, to the point of more or less stalling the LFO. The trimmer allows an adjustment to set a maximum depth vs. maintaining a usable minimum rate. You could also record the resistance from the trimmer, and hardwire a resistor across the poles as well, but using a trimmer on the pot is my fav, rather than a resistor, allowing me to go in a tweak things whenever I like. You may also place the trimmer across poles 1 and 2, thus reversing the action of the pot. I found that to my tastes, the trimmer is somewhere between 5K and 10K. If that's too low for you, then jump up to a 25K or 50K trimmer. I made a quick video of the mod, here it is;

Enjoy!

I'm going to bed less stoopid again tonight  

[pinkjimiphoton]

of course we need video and audio clips!!!

[digi2t]

of course we need video and audio clips!!!

Sorry bro, was updating my last post when you wrote in. I added a mod. Look again.

[pinkjimiphoton]

OH HELL YAH!!!!!!!!!!!!!!

GONNA DO THIS TODAY!!!!

[digi2t]

of course we need video and audio clips!!!

OK, here ya goes. New video, overall operation, including LFO mod. Sounds almost like an Uglyface, with a speed control. I decided to get a little freaky at the end  Enjoy!

[pinkjimiphoton]

killer...dude, that think is f'n sick now!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

sounds like it's puking underwater on neptune, where the atmosphere is pure lsd.


or something. nice!!

[deadastronaut]

sounds much better with the depth control.....nice one!...

[Ronan]

Sounds great Dino!

Fair enough on the LED's. I have used them a bit in tube amps. They can be used as constant voltage sources like a zener, I was thinking of using 2 x plain old lo-bright 1.8V leds in series to make 3.6V instead of 3.5V for the zener in the Mr Multi cct, if I can't find a 3.5V zener that is. Haven't looked for one yet.



I did some minor cleaning up on the PCB and an overlay, neither verified as yet. Add them to your documentation if you want or wait till I verify. I went right over the schem to do the overlay using a highlighter for each component, so it *should* be very close to good to go. I can't work out the battery wiring, it enters through a hole into the PCB as a twisted pair and I gather the red and black wires were simply soldered onto the copper in the right places underneath the PCB, but the black wire should originate from the earth on the input jack, so I'm just a bit lost on that detail, but its certainly no show stopper.

I got to try the ceramic caps in the EH talking pedal, impressions are that they are smoother, and slightly less gain in the signal. Very interesting. Less in your face, less raspy perhaps. A very noticeable difference. I am not sure which I like best, in your face with strong almost ragged edges or a smoother "cooler" sound. The effect still remains strong either way. In this Mr Multi circuit, it looks like they are using poly caps in the JFET feedback position only, and ceramics for the filters. I also agree with you that those greencaps look a lot bigger physically than a 2n cap, and its quite possible 22n would be more likely (with a 223 marking on them). Although your pedal currently seems to have nailed "the sound" of Jimi's original pedal, so its also possible 2n is correct? I might do a breadboard version before soldering up the PCB, I want to play with the feedback resistors which are external to the PCB, and try to measure what is going on with the JFETS and that 3.5V bias voltage.

[digi2t]

Fair enough on the LED's. I have used them a bit in tube amps. They can be used as constant voltage sources like a zener, I was thinking of using 2 x plain old lo-bright 1.8V leds in series to make 3.6V instead of 3.5V for the zener in the Mr Multi cct, if I can't find a 3.5V zener that is. Haven't looked for one yet.

If LEDs work then that's fine. The zener number that I've listed in my vero is what I used. It's a 4.1v zener, which gives a bias voltage of 3.8v when the circuits powered up. It works perfect. On the original board, the number is printed on the board, stating a 4v zener, but I never did find one. They all jump up by 3's (3.3, 3.6, 3.9, 4.1, etc.). The 4.1v got me closest to bias than any of the other ones. Trust me, I tried them all.

I took another look at a picture of the board, and it looks like the positive is soldered right to the board, but I can't tell when the heck the ground is going. Although, there's lots of room on the board to drill another hole.

Very thoughtful of you to do an overlay with the components. I just recieved a PM from Greg concerning this, and since mine is so fuzzy, I'll give him a heads-up to this one. You rock man!

Let me know how the resistor experiments turn out.

Cheers,
Dino

[Ronan]

The zener number that I've listed in my vero is what I used. It's a 4.1v zener, which gives a bias voltage of 3.8v when the circuits powered up. It works perfect. On the original board, the number is printed on the board, stating a 4v zener, but I never did find one. They all jump up by 3's (3.3, 3.6, 3.9, 4.1, etc.). The 4.1v got me closest to bias than any of the other ones. Trust me, I tried them all.

Aaah, OK, I didn't know that you tried a heap of those zeners. I was just assuming the 3.5V zener voltage stated on the schem. All good then. Give me a few weeks and I might have something up and running. I'm really looking forward to hearing it.

[pinkjimiphoton]

guys, if ya wanna tell my newb ass what you need, i can check it on mine, too for ya if anything is unclear on schems, gut shots, or layouts.

[Ronan]

guys, if ya wanna tell my newb ass what you need, i can check it on mine, too for ya if anything is unclear on schems, gut shots, or layouts.

Actually yeah Jimi, any chance of confirming the value of the caps with the green and red on them, if you haven't already? The green ones might all be marked 222 or 223, and the four ceramics (marked in red) might be marked 104.

Also would it be possible to measure the voltage from the pink arrow tip to ground (the input jack ground might be a good place to get a good ground). I am curious to know what bias voltage your original unit is running with, and this will measure that bias voltage. Thanks mate, and no hurry.

[pravudh]

Hello,I build with Ian's layout. I use TLC27M2 (Dual Precision Single Supply Low-Power Operational Amplifier)for LFO chip.The speed range very smooth and better than general opamp.I set bias about 3v5 by measuring at middle lug of trim pot to ground.