Joyo - JF-13 AC Tone  [schematic]

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Mickyvai
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Post by Mickyvai »

Hi everyone. I performed the speaker sim mod and thought that someone here could use a schematic of the mod that was previously explained, with all the details specified. ;-)
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speaker sim ON-OFF.jpg

Mickyvai
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Post by Mickyvai »

I have done a short demo of the mod:

[youtube][/youtube]

ericlaw02
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Post by ericlaw02 »

Has anyone traced the full schematic of the Joyo circuit for differences against the Tech21 originals (https://www.freestompboxes.org/viewtopic ... 01#p220001), other than the R4/E1/Cin/C2... components?

I replaced the components to create my own "VT Bass", the tone seems identical to YouTube videos with each setting, but it seems lacking in gain, and with noticeable increase in noise.

For example, an actual VT Bass unit can achieve unity gain when EQ is flat, drive at 10 o' clock, when level is set to 8-9 o' clock, yet on my modded Joyo, I have to turn to around 2-3 o' clock to achieve unity gain. So somewhere there's at least some difference between the two circuits.

For starters, I checked the circuit/component values after the final opamp output, and they seemed identical, so it's not that simple unfortunately :(

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Post by ericlaw02 »

I think I may have answered my own question about the lack of gain.

On the original Tech21 schematic, with R19=10k and R20=100K, IC3a provides 10x voltage gain (20db gain). But on the Joyo, the corresponding components being R30=10k and R31=15k, it should only provide 1.5x voltage gain (~3.52dB gain).

I know nothing about electronics, but I suppose R31 is the culprit for the lack of gain, replacing it should allow me to match the original's levels. Though I don't really think that's going to help reduce the noise...?

Still, I'm interested if anyone found out any other differences between the two boxes...

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Post by Hanky- »

ericlaw02 wrote:I think I may have answered my own question about the lack of gain.

On the original Tech21 schematic, with R19=10k and R20=100K, IC3a provides 10x voltage gain (20db gain). But on the Joyo, the corresponding components being R30=10k and R31=15k, it should only provide 1.5x voltage gain (~3.52dB gain).

I know nothing about electronics, but I suppose R31 is the culprit for the lack of gain, replacing it should allow me to match the original's levels. Though I don't really think that's going to help reduce the noise...?

Still, I'm interested if anyone found out any other differences between the two boxes...
I found that R31 measured 22k on the actone while the california sound had 68k in that place.but the calif has added mic sim components which lower the overall volume so removing those to match the actone gave me significant increase in volume.

After trying out different values in R31, 47k sounded good to me without affecting the tone much or the dynamics. My guess with the noise in joyo is the buffer design might be the culprit since it isn't the same as the tech 21 or perhaps maybe it's the board quality in the joyo being sub par. I even replaced the ICs to match the tech 21 but it didn't lower the overall noise.

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Post by pjk »

Ripdivot wrote:Remove the part shown and add a jumper wire duplicating the switch in the down position.
Hi and thanks very much for doing this. If i am not wanting to add the switch, does the jumper wire go from pin 3 on the volume pot to R24 or is it to the point adjacent to the 0 ohm resistor please ?

jswnhart
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Post by jswnhart »

jockie wrote:
Ripdivot wrote:I had some time so I sat down and figured out the speaker sim bypass on the newer PCB.

WARNING: be very careful with your soldering, the traces on the board are very fragile.

I used 26AWG wire for my connections. Start by removing the 0 ohm resistor shown. Solder a wire to each of the three places shown in red. Once your wires are in place put a small blob of hot glue over the connections to the board. I didn't do this to the wire soldered to pin 3 of the level control as it is plenty solid. solder the other end of the three wires to your switch and you are good to go. Works great!
Hi, thanks for that. I did it on my American Sound (Harley Benton, not a Joyo, but the pcb is the same). It works great.
But, to avoid the immense differences in volume in both positions of the switch, I took a DPDT-Switch. One area of the switch I soldered as you mentioned, the other area switches a resistor between the first and second lug of the volume pot (from left to right in your picture) when in SpeakerSim OFF position.
To get the right value of the resistor I soldered two lugs of a 10k-pot instead of a fixed resistor and turned it as long as I got nearly the same volume in both positions. Then I disoldered the 10k-pot again and measured the resistance between the affected two lugs. In my case it was around 3k3. So I soldered a fixed 3k3 resistor instead of the 10k-pot and it works great in all positions of the Volume-pot. Maybe values between 2k2 to 3k9 will work. Just have a try or do it with a potentiometer like I did.
Note, that this resistor is not affecting anything, when in SpeakerSim ON-position.

Thanks again for your work on the new pcb-layout - now it is a very versatile component of my pedal-board.

Music is the best
I did a similar approach, but used a 1M pot in series with the wire from R24 to the “off” side of the SPDT switch.
180K seemed to equalize the volume between the “on” and “off” positions.
Still have a big tonal difference between settings. Has anyone addressed this?

Hanky-
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Post by Hanky- »

The value of R24 in the American Sound I have in hand is 39k instead of 33k as reported earlier, anyone else have one in hand that would like to crosscheck this?
It sounds like the ones in the demo vids I found online.

I tried 33k in there, I sounded less fendery sort of but could be dialed in to sound closer. I might try changing it later to the 47k as the tech21 to hear the difference cause I liked the 39k in there better.

ChristianSosa
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Post by ChristianSosa »

Hello Guys!

Does any of you know the value of R24? I kinda lost mine... somehow...

Antigua
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Post by Antigua »

ChristianSosa wrote:
24 Mar 2020, 02:25
Hello Guys!

Does any of you know the value of R24? I kinda lost mine... somehow...
R24 is 33k

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Post by Antigua »

I performed this mod tonight. Killer results. It's a shame they don't come stock this way. Does anyone know if the cab sim bypass procedure is the same for all four of the Joyo - Tech 21 amp sim clones?

I notice a lot of people pull these mods off with 24 AWG stranded wire, I've ordered some 30 AWG stranded, which is harder to come by, but I think it will make hacking SMD connections a lot easier.

The suggestion to use hot glue to hold the wires in place after soldering is a game changer, because I was very worried that the teeny tiny SMD solder joints would break when I went to put it back together again. The glue holds the wires real well. Unfortunately it didn't occur to be to only glue against parts of the board were there are no traces or components until after I was done. The manufacturers placed glue over some components, for example over the battery wires, but their glue is very soft while the hot glue dries hard. If I were to remove it now, it would surely rip the SMDs and the traces that underneath it, so that was a one way ticket with the hot glue.

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Post by Antigua »

Upon further use with the Actone on cab sim bypass, I've found that the treble is hard to tame. With bright single coils, it can be almost impossible to dial out the treble. I created a bode plot of the response of the pedal in order to get a visual of what's happening:

Image

The black line is stock condition. The blue line is with bypass, everything at 12 o'clock. The red line shows it in bypass mode also, but with the treble "at zero" and the bass "at ten", and it can be seen that in bypass mode, the bass control is still very attenuated below 100Hz, and although the treble comes way down, the flatness of the slope yields a bright, thin sound compared to the more abrupt drop off with the cab sim engaged. Also, most of that treble attenuation is weighted at the bottom of the sweep. I might try putting a "bright cap" in there to try knocking down that treble bypass mode.

tl;dr, the mod opens the pedal up to new sounds, but the EQ becomes much more limited.

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Post by Antigua »

I was just experimenting with treble attenuation with the cab sim bypass mod, and I found that a 3.9nF cap across the volume lugs along with the resistor gives pretty good results. The treble sound like it attenuates around 4kHz, so it's still plenty bright, but it takes away the raspy noise. I've modified the diagram posted by Mickyvai:

Image

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Post by Antigua »

I've made this mod to all four of the Joyos. The Actone, American and British are all very similar, but the California model has some different circuitry. This is all four in bypass mode:

Image

So in bypass mode, three of them are essentially the same pedal, and even when the cab sim is activated, the frequency response plots are still not dramatic. The California model though, has a significantly different response curve. One visual piece of evidence that they differ is the "C6" electrolytic capacitor is present in the California, but is missing from the other three models.

This is the board of the California model with the mod in place:

Image

One important difference with modding the California is that the "0" surface mount resistor is instead 2.2k ohm resistor, and I did not remove it, and the mod works fine with that 2.2k resistor just left in place.

Here they all are with the little toggle at the top:

Image

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Post by Hanky- »

Antigua wrote:
17 Jun 2020, 07:37
I've made this mod to all four of the Joyos. The Actone, American and British are all very similar, but the California model has some different circuitry. This is all four in bypass mode:

Image

So in bypass mode, three of them are essentially the same pedal, and even when the cab sim is activated, the frequency response plots are still not dramatic. The California model though, has a significantly different response curve. One visual piece of evidence that they differ is the "C6" electrolytic capacitor is present in the California, but is missing from the other three models.

This is the board of the California model with the mod in place:

Image

One important difference with modding the California is that the "0" surface mount resistor is instead 2.2k ohm resistor, and I did not remove it, and the mod works fine with that 2.2k resistor just left in place.

Here they all are with the little toggle at the top:

Image
Remove R29, it should be 6.2k in value. That should get the mic sim to be less present when doing the cab sim bypass on the California sound. R28 measured 22k on mine, I wonder if they changed that value lately.

Also with the mic sim gone, the pedal will be alot louder due to the the value of R31 being 68k, reducing that to 22k, should give the same volume as the American sound. The American Sound with the Cali mic sim & R31 values is quite a modern sounding pedal.

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Post by Hanky- »

I modded my Cali sound with a bunch of mini dpdt switches to get for pedals in one housing, so basically I hve the american, actone, british & cali in one box under the hood. I considered using panel mount toggle switches but that would require a bunch of drilling, these pcb type dpdt mini switches were easier to just hot glue on the back of the pcb. I did add a cab bypass switch in there too but didn't take recent pic of it. Few more(4) could get me the oxford in there as well but I'm not a fan of that pedal much.

While at it, I put in new electrolytics throughout most places, just cause I had some with me & this pedal was from 2012 stockpile, figured I leave new ones in there.
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287m
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Post by 287m »

Antigua wrote:
14 Jun 2020, 03:32
I was just experimenting with treble attenuation with the cab sim bypass mod, and I found that a 3.9nF cap across the volume lugs along with the resistor gives pretty good results. The treble sound like it attenuates around 4kHz, so it's still plenty bright, but it takes away the raspy noise. I've modified the diagram posted by Mickyvai:

Image
Can this mod applied for all Joyo? Same value?

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Post by Antigua »

287m wrote:
18 Jun 2020, 19:49
Antigua wrote:
14 Jun 2020, 03:32
I was just experimenting with treble attenuation with the cab sim bypass mod, and I found that a 3.9nF cap across the volume lugs along with the resistor gives pretty good results. The treble sound like it attenuates around 4kHz, so it's still plenty bright, but it takes away the raspy noise. I've modified the diagram posted by Mickyvai:
Can this mod applied for all Joyo? Same value?
Yes, I did the exact same mod on all four of the models. The only significant difference is the California model, the you don't remove that R28 "0 resistor" from the board. On that model it's actually a 2.2k ohm resistor and it does something important.

The value of the cap, I used 3.9nF, sets the low pass frequency. There is still a lot of treble with the 3.9nF cap, but it's not as noisy. If you use a higher value, more treble will be dropped, so it's a matter of preference.

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Post by Antigua »

Hanky- wrote:
18 Jun 2020, 18:01
I modded my Cali sound with a bunch of mini dpdt switches to get for pedals in one housing, so basically I hve the american, actone, british & cali in one box under the hood. I considered using panel mount toggle switches but that would require a bunch of drilling, these pcb type dpdt mini switches were easier to just hot glue on the back of the pcb. I did add a cab bypass switch in there too but didn't take recent pic of it. Few more(4) could get me the oxford in there as well but I'm not a fan of that pedal much.

While at it, I put in new electrolytics throughout most places, just cause I had some with me & this pedal was from 2012 stockpile, figured I leave new ones in there.
I don't really know what sets all four of them apart, let alone that it's possible to get all four versions working on one board. How did you figure out what to do to make it work?

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Post by JiM »

By reading the big "Character Series" thread, all the schematics and comparisons between models from Tech21 and Joyo are there :
viewtopic.php?f=1&t=6571&hilit=characte ... =80#p71872
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