Joyo - JF-02 Ultimate Drive "2010" MISTAKE [schematic]

[Intripped]

[...] By the way,it is my understanding that this method uses the internal silicon diode between source and drain,no big deal compared to normal diodes...

Yes, I agree.

[Intripped]

PS: ...even if I've never made a listening comparison between a usual silicon diode (1n4148, 1n4007, ...) and the mosfet's internal diode.
Who knows, maybe there actually are some little differences.

One difference i know, is that If I measure the fw voltage drop with my multimeter I get:
Around 700 for 1n4148
Around 670 for 1n4007
Around 620 for 2n7000's internal diode (S+G and D)

But still I know nothing about the clipping "knee"

[Intripped]

Sorry for triple posting...
I've found an interesting discussion, expecially reply #68, here is the link

[DavidRavenMoon]

I just picked up one of these pedals... it was $20, including shipping! ($17 and change). I've tried an OCD and actually hated it. It's got this harsh quality that sounds like op amp distortion or something. Why are they so popular? Makes me wonder why I bought this! lol

Anyway, I read through this thread, and decided to flip the diode around. I notice from looking at ODC schematics that compared to the OCD, both MOSFETs are backwards in the Joyo. After I had the diode out, on the end of my hemostats, it decided to make a run for it! Even after sweeping the floor I could not find it! So instead I just inserted a jumper in its place. I also soldered a 1M resistor across the two output lugs of the gain pot to reduce it's value to 500k. Now I have a bit more useable range and less gain on the low end. I also changed the tone cap to .047µF, as I felt it got too dark. The smaller value doesn't really help much!

Now I kind of like the pedal on the lower gain end, and with the gain about 12:00 it can get a Big Muffish tone. But I'm thinking it still needs some lows rolled off the inout, so I might reduce the input cap value, and I notice it lacks the 10k resistor after the input cap as compared to the OCD. So maybe a little resistance there would help.

[obieito]

Hey, just wanted to post a follow-up on my experience with this pedal. I have the same PCB version and bought my pedal at some point last year. When I took it apart today, the diode was going the correct way. So it seems they did (at some point) figure out the issue.

Same here.. Just wanted to share that I got mine around summer 2016 ant the diode came already in the corrected position.

Thanks all!

[DavidRavenMoon]

It sounds much smoother without the diode. There's something about the OCD I never liked. And it's that diode. Gives it a hard edge I didn't care for.

[howmuch]

Hey, just wanted to post a follow-up on my experience with this pedal. I have the same PCB version and bought my pedal at some point last year. When I took it apart today, the diode was going the correct way. So it seems they did (at some point) figure out the issue.

Same here.. Just wanted to share that I got mine around summer 2016 ant the diode came already in the corrected position.

Thanks all!

Out of interest, have they corrected the silkscreen and the diode?
Or are you saying the diode is now fitted opposite to the direction shown on the silkscreen?
A clear photo would explain a lot.

[DavidRavenMoon]

Out of interest, have they corrected the silkscreen and the diode?
Or are you saying the diode is now fitted opposite to the direction shown on the silkscreen?
A clear photo would explain a lot.

No. But the transistors are also reversed as compared to the OCD, so the diode is not actually in backwards.

[alblupo]

I can confirm that in 2017, at least in the one I bought directly from China, the diode is still reversed... thanks howmuch for pointing it out long ago!

[potul]

Hi

I just want to thank the OP. I checked my Ultimate drive, and it also had the diode reversed. I did the modification and flipped it, and for sure it has lost some harshness. It now has some less highs, and can be a little muddy at the same settings. But playing with the tone control I can dial a good tone.

I'm not certain if really it will make a big difference, but for sure this is how the circuit was ment to be.

Thanks again

Mat

[schematic searcher]

I did several tests with clipping diode configurations during the last year. Unfortunately I didn't find this thread earlier, since it contains some useful information and would have saved me some time.

Nevertheless I feel like sharing some of my own insights.

I own two UDs, the first one I modded to be even more OCDish (V4). This one I prefer in front of my really cranked Marshall. It provides a llittle less gain, is less boomy and therefor more accentuated or detailed, call it what you will.
The stock UD I like in front of my really bad sounding little 15W transistor practicing amp to get some kind of amp sound. Here the more distortion, more bass, darker tone of the stock UD seem to fit better.
In both of mine UDs the Ge-diodes were reversed and therefor useless, because they are blocking the body-diode of the serial Mosfet. This means
we are dealing with a one (silicon) diode asymmetric clipping configuration, as already mentioned earlier in this thread. So I reversed the Ge diode to get the intended three diode asymmetric clipping.
But in contrary to some predecessors, it didn't make that much of a difference to me, which lead me to further experimentation. I tried a lot of different configurations (1,2,3 silicon; 1,2,3 Germaniums; BS170 Mosfets; 1,2,3 LEDs in different colours, to mention a few of them) and in the end I'm not able tell which I really like best. Okay, I'd say it has to be a three diode asymmetric configuration, perhaps three Silicon diodes...
I also like it with all clipping diodes removed, which produces a slightly more open sound.

My personal conclusion is that at least in the Ultimate Drive the clipping diode configuration doesn't drastically alter the sound. I think the overdriven Op-Amp TL082 lets the pedal sound like it sounds and if you don't like the pedal you likely won't like it either with the Ge flipped around. You might tinkering around with the clipping diodes, if you have fun doing this, but you don't necessarily have to.
But again, this is my personal opinion and might depend on my playing style and setup.

Here is what I found out concerning the drain/source+gate connection and Mosfet-clipping question.
In contrast to the schematic on the real PCB gates and sources are connected resulting in the fact that the inherent drain-source body diodes of the Mosfets act as clipping diodes. As far as I found out this is also true for OCDs, although I have to admit that I don't own or disassembled an OCD yet.
The body diodes are, behave and sound like simple silicon diodes. There is no magic, mystery, moyo, voodoo mosfet clipping going on here.
Anyway, if drains and gates were connected, as the schematic says, wouldn't alter the behaviour of the circuit, because the Mosfets are connected antiparallel and therefor the body diode of one Mosfet is parallel to the other Mosfet and vice versa, and body diodes have a forward voltage of 0.6V and therefor conduct much earlier than the Mosfet itself.

I think Fulltone implemented Mosfets in the clipping stage for advertising reasons and Joyo just copied it.

Additionally I wanted to check the real Mosfet Clipping, but didn't find the time to do so yet. As far I remember there are two or three methods to achieve a real symmetrical or asymmetrical Mosfet clipping stage.


I tumbled over this thread, because a few days ago I played around with my modded Ultimate Drive and recognized that if Level is turned all the way down, it not only cuts down the drive signal, but also the dry signal (pedal bypassed). The signal blends in from zero to about 8 o'clock, after 8 o'clock it remains on the same level.
Of course this is not the normal working condition, but I'd like to fix this obvious malfunction. I have the feeling that it is a bypass issue.
I thought it could be an unwanted ground connection, but the error persists even with the PCB removed from the chassis. I also checked the 3pdt switch and it seems to work properly.

I'd appreciate anybody giving me a decisive hint or a starting point to fix this problem.