A Clone of Half of an Ibanez Jemini

[rmjlmartin]

Hi everyone, and thanks in advance for your help. I'm new to the forum (and forums in general), and this is my first post, so please bear with me if I don't get everything  quite in the best format.

Just a quick summary of what I'm looking for-
My go-to drive pedal is a stock Boss DS-1, and my second is the red (distortion) side of an Ibanez Jemini, which was a Steve Vai signature pedal from a few years back. The Jemini is a double-sized pedal, so it takes up a fair amount of real estate on my pedalboard, and I only use the distortion side, so I'm trying to clone it or find something really similar that's a single-space sized pedal.

From what I read online, the distortion side is supposed to be based on a modded DS-1 (and Steve is known for using a DS-1 with the Keeley Seeing Eye mod), and the overdrive side is supposed to be a modded Tube Screamer. I have a second DS-1 that I'm hoping to mod to be at least pretty similar to the distortion side of the Jemini, and Ibanez was kind enough to give me the schematic for the Jemini, since it's a discontinued pedal, but my knowledge of reading circuits is basic enough that I can't figure it out on my own.

So, my questions are first, can I mod a DS-1 to be the distortion side of the Jemini, and if so, what will it take to do it? I know that I'll have to change the chip, since the Jemini uses an RC4558DD, but I'm having trouble with figuring out much more than that.

I've attached the schematic to this post. Hopefully that's acceptable by the forum guidelines, since Ibanez is willing to give it out for the asking?

[HamSandwich]

Hello rmjlmartin,

Welcome to the forum! I don't have a ton of experience with the DS1, so this info is just basic research. Those who have worked more closely with it may have different, and probably more accurate, views.

There are a few variations of the DS1 circuit out there.

https://www.electrosmash.com/boss-ds1-analysis

and this copy of a 1980 schematic

https://i.pinimg.com/originals/77/1c/13/771c13a12b30ac47733ce1a21fdb27eb.jpg

and while the idea is the same as your Ibanez pedal, there are quite a few differences. Is there a way to get them close enough? Maybe, but I'm not sure. Some of the major issues are the variations in DS1 circuits. For example, that 1980 schematic uses a single opamp TA7136p chip, while the electrosmash uses a dual opamp. Your Ibanez uses a dual opamp, but only one of the opamps, the one driving the diodes to cause the distortion, is used in the same way. In your pedal, the second opamp is doing some strange gain after the tone control (maybe) while the opamp in the electrosmash circuit is buffering the one driving the diodes.

The Ibanez also has some transistors in the tone circuit which I have no idea what they are doing there.

A final nail in the coffin would be nearly every passive component has a different value when comparing the schematics. The elelctrosmash and the 1980 copy are similar in this respect, but the Ibanez is quite different. The amount of time it would take to remove all of those components and replace them would be crazy, not to mention the risk of pulling traces and burning bits if you are inexperienced (and even if you are experienced, desoldering is no fun task). Do all of these components actually need to be changed / have an effect on the sound? Maybe. There are probably a few major changes, but the accumulation of smaller changes may effect the overall feel.

In my opinion, if you really wanted just the distortion side, get a blank DS1 pcb from one of the manufacturers in the links above (not sure who sells a DS1 PCB, but I know I've seen it!) and work out what parts to put where to make the Ibanez circuit as closely as possible. An issue is going to be that Ibanez tone control, hopefully someone can shed some light on what's going on there besides it being active.

[Willybomb]

Aion do the DS-1 pcb.

[Scruffie]

Yeah HamSandwich is right, while the core gain circuit is the same, its tone is shaped by a gyrator EQ which is nothing like the original.

You could tweak the component values of the core distortion circuit to match up, without the tone shaping it might not sound how you want though.

It'd be far easier to start with a fresh layout if you wanted a 1 to 1 clone, thankfully, there's plenty of info on the forum to get you started

[fair.child]

I agree with Scruffie. You got the schematic so you got all you need to start the EAGLE board either one side or two sides it's your choice.

[rmjlmartin]

Thank you all.

I was wondering how complicated it would be when I saw that the difference was more than a few caps and resistors. I just don't know enough about the circuits to know what all is important or exactly how it works.

And I was going to ask in the post if I might be better off starting with a DS-1 pcb or kit, but I forgot.

So, if I'm understanding you correctly, there isn't a really simple way to make the half a Jemini from a DS-1 circuit?

I'll look into the EAGLE board.

Are there any other pedals/circuits that come to mind that are similar? I've come close to getting the same tone with a Boss MD-2 and a Marshall GV-2 Guv'nor.

[fair.child]

For the TS part, you can consider Green Bean. For DS-1 part, you might want to etch the PCB. There are quite few DS-1 PCB clone which you can do more research per your liking.

[culturejam]

Yeah HamSandwich is right, while the core gain circuit is the same, its tone is shaped by a gyrator EQ which is nothing like the original.

Kinda reminds me of DOD stuff from the lat 80s / early 90s with the gyrator.

[reddesert]

There is a lot going on in that schematic, but some of the complexity is due to the Ibanez switching scheme and so on, and can be disregarded for purposes of cloning it.

The stuff in the bottom left with the CMOS gates (labeled CD4011) and other ICs is all for the soft touch switching.  The stuff in the boxes at bottom right is for switching multicolor LEDs. These can be ignored.


There is a little bit of power supply circultry on the left middle that is needed to provide +9V and +4.5V (the resistors and caps around C42, C43, C45).

The signal path runs from the input at middle left, to an input buffer Q1, then through one of three parallel paths. From top these are overdrive (Q5 - U1 - Q8), bypass (Q2-Q3), and distortion (Q9-Q10-U2-Q13, also Q11 and Q12). Then these are combined and go through the output buffer Q4.  Q's are transistors and U's are integrated circuits.

The transistors that are shown by a horizontal bar with an arrow pointing to it, Q9 and Q13, are JFETs, and are used for the switching. You can ignore these and the adjacent diodes.

The part of the circuit that is shaping the distortion sound is from C19 through C34. This is what you would need to duplicate. The signal also runs through the input/output buffers Q1 and Q4, but those probably have little or no effect on the sound and you may be able to leave them out.

If you don't want to design a PCB, you could try posting the schematic in the Requests forum at tagboardeffects.blogspot.com, and someone might draw you a stripboard layout.

[rmjlmartin]

Thank you all, especially reddesert. That's very helpful.

I'm sorry, this turned out to be a very busy week and I haven't had time to keep up with this thread or explore the different board options. (I'm actually out of town at the moment, too, but I finally had time to log in and look this back up.)

This definitely looks promising, and I guess another plus is that my spare DS-1 can go under the knife to try some other mod.

[rmjlmartin]

Hi again, everyone.

I've finally got a schematic drawn here. I downloaded the free version of the Eagle software, but I haven't had time to go through the whole tutorial to figure out how to do it, so I drew up one by hand for now. I've attached it to this reply.

The added switch (S1A, S1B) is to switch the buffers in and out of the circuit in case it does actually affect the tone. And, getting ready to post this, I already see one error- There should be a break between the front side of both of the switches and where it goes back into the buffer, right? Does it look like it should be correct otherwise?

I also haven't noted any of the component values on my hand-drawn schematic yet. Hopefully it's readable enough? This is the best I could do with my scanner with the size limit for attachments.

Thanks!

[xdyun]

I know his is an old thread, and his post makes meregister in this forum,and Any chance of posting the schematics again?

[Willybomb]

Save the PDF linked in the first post.