#1
I see this get mentioned from time to time on here and other forums, but there’s a surprisingly small amount of actual information on how to go about converting a 308 to 250 specs, other than “change the IC and a cap” and not everyone is schematic savvy enough to look at those and understand what needs to be done. The fact that people pay 500 bucks on eBay for the originals, when a $30 reissue can do the same thing backs that up a bit. The conversion is easy. Not quite as easy as the internet makes it sound, but if you’ve done work to the innards of your Crybaby or Tubescreamer, you’ll have no problems here. In fact, it’s easy enough and cheap enough, you’ll wonder why DOD just didn’t do it right in the first place. I’m not that familiar with Yngwie’s work, but if this is his pedal of choice, I can only assume that his recordings sound like jabbing a No. 2 pencil in your ear. Hopefully, those googling for a how-to will find this and I can feel like a big man for posting a how-to on the internet.

What you need:

Soldering iron
Solder
De-soldering braid
2-3 inches of insulated wire
LM741CN op amp(or a 1458 if you don’t want to modify the PCB)
IC socket
0.01uf capacitor
0.056uf capacitor

Small list, isn’t it?

OK, I’m going to assume you can handle opening your pedal and removing the PCB without me walking you through it. Lay the board down in front of you and locate C1, C2, C3 and the 4558 op amp(black box with 8 pins on the side). That’s what you’ll need to remove. Toss them in your parts box and sell the 4558 op amp to one of your mojo obsessed buddies for more than it’s worth. You then want to solder the 0.056 cap into C1 and the 0.01 cap into C3. C2 will stay empty.

On to the op amp. This is where you need to decide if you’re man enough to cut and re-route a few traces on the PCB, or just want to plug and play. The 741 is arguably the source of the original grey 250’s tone, but since it has a different pin layout than the 4558 it replaces, you can’t just solder it in without modification. The 1458 does have the same layout as the 4558 and is said to sound “close” to the 741. I haven’t tried the 1458 myself, but if you’ve gone this far, you might as well follow through and use the 741. If using the 1458, solder in the IC socket and plug the 1458 in, making sure it’s in the same orientation as the one that came out. You can now put your pedal back together and bask in the glow of almost modding your pedal to 250 specs.

Now, if you think you have the sheer testosterone to mod the PCB, read on. There are several traces you need to cut before you install the op amp. When the op amp is on the pcb, the pins are laid out like this:
1-----8
2-----7
3-----6
4-----5

Flip the PCB over to the soldering side. Remembering that the pins will be reversed with the board flipped over, cut the trace that runs between pins 5 and 7, the trace that runs from pin 8 to R5, the trace that runs from pin 1 to C5 and the trace that runs off of pin 6(be careful not to break the trace it connects to). Solder in the IC socket. You will then need to run a bit of wire from pin 6 to the top of R2(use the top hole from the C2 cap you removed for this) and run a wire from pin 7 to the top of R5. See the picture if none of this nonsense makes any sense. Insert the 741, making certain it sits in the same orientation as the 4558 was. And just like that, you’re done. Put you pedal back together.




How’s it sound? If you did everything right and aren’t completely deaf, you’ll immediately notice a profound improvement. You suddenly have low end again, and your ears aren’t bleeding from the highs. You’ll also notice a completely different character to the gain the pedal produces, for the better. Is the tone you’re getting worthy of the insane eBay prices? No. Those guys are nut bags. But it is worth 30 couple dollars you paid for the pedal and mods? Yes, several times over even.

I should note that the schematic on Fuzz Central lists C5 as a 10uf value for the 250. Stock in the 308 is a 4.7uf. I’ve looked at pictures of probably a dozen or so “grey” PCB’s while reading up on this and every grey 250 I’ve looked at has a 4.7uf there. These old pedal weren’t exactly built to tight specifications, so it’s entirely plausible that some of them had a 10uf. It’s up to you if you want to experiment with swapping it out. And if you’re feeling especially frisky, you can try different diodes in D1 and D2. LED’s are supposed to give you a warmer sound, but I haven’t tried them, so I can’t say.

Also, if you hate the DOD style power jack, now’s the time to swap it out for a Boss style. You’ll need to drill a larger hole in the case to accept the larger jack.

Finally, if you’re like me and hate using gear with someone else’s name on it, use some nail polish remover and wipe off Yngwie’s name and signature.

Last edited by Jason43 at Nov 27, 2009,
#3
sweet temped to buy one now, clips?
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Gear:
Esp Ltd Ninja 600
Esp Ltd F-50
les paul elite
5watt jcm800 clone
Roland jc-55
Crate V33
Jca20H
Ibanez tubescreamer ts9
Keeley ds-1
#5
Thanks, I will try this mod on my stock YJM308 using the 741 op amp. Looks easy enough.

You know the area between DOD and the footswitch where you removed "Yngwie J. Malmsteen" would look cool substituted with a big color matching 250 decal using the same font as the Preamp Overdrive text below.
Fender Malmsteen Strat > Boss NS2 Noise Suppressor > NS2 Send > NeoClassic 3080 Compressor > NeoClassic 741 Overdrive > NS2 Return > NS2 Output > VHT Special 6 Ultra Amp > Amp Send > MXR Carbon Copy Analog Delay > Boss RC3 Loop Station > Amp Return
Last edited by Yngwie#1 at Dec 31, 2009,
#6
Quote by Yngwie#1
Thanks, I will try this mod on my stock YJM308 using the 741 op amp. Looks easy enough.

You know the area between DOD and the footswitch where you removed "Yngwie J. Malmsteen" would look cool substituted with a big color matching 250 decal using the same font as the Preamp Overdrive text below.


I thought about that and actually looked for some gold dry transfer numbers. I think in the end I like people not knowing what it is.
#8
Quote by Jason43
I thought about that and actually looked for some gold dry transfer numbers. I think in the end I like people not knowing what it is.


Yeah let them wonder what is that mystery 'mojo' pedal giving that smooth overdrive.

Do you have any sound clips of what it's like after the mods?
Fender Malmsteen Strat > Boss NS2 Noise Suppressor > NS2 Send > NeoClassic 3080 Compressor > NeoClassic 741 Overdrive > NS2 Return > NS2 Output > VHT Special 6 Ultra Amp > Amp Send > MXR Carbon Copy Analog Delay > Boss RC3 Loop Station > Amp Return
#9
No I don't. I need to replace my mixer and don't have the means to make a decent clip without it. It is a major improvement, not a "I think I can hear a difference" kind of improvement. If you like the extreme brightness and thin low end of the 308, I'd leave it as is since this deletes both of those traits.
#10
I just want to make sure I get the right chip since I don't want to mod the PCB... Is it an LM1458CN? While I took several classes on electronic circuitry, I never really learned anything about the naming conventions for ICs...

Also, does anyone have any suggestions on where to get components? I can't seem to find any local shops.
Last edited by Aurora900 at Jan 6, 2010,
#11
Quote by Aurora900
I just want to make sure I get the right chip since I don't want to mod the PCB... Is it an LM1458CN? While I took several classes on electronic circuitry, I never really learned anything about the naming conventions for ICs...

Also, does anyone have any suggestions on where to get components? I can't seem to find any local shops.



If you're not going to use the 741 chip and modify the PCB, that chip will work. Make sure you do use the chip socket. It will keep the op amp from being damaged by heat from the iron.

This place should have everything you need:
http://www.smallbearelec.com/StoreFront.bok
#12
What about differences between part brands for the 741 op amp and capacitors, and even replacing any other parts in the YJM308 that may be low quality? Has anyone tested to that level to hear any tone change?
Fender Malmsteen Strat > Boss NS2 Noise Suppressor > NS2 Send > NeoClassic 3080 Compressor > NeoClassic 741 Overdrive > NS2 Return > NS2 Output > VHT Special 6 Ultra Amp > Amp Send > MXR Carbon Copy Analog Delay > Boss RC3 Loop Station > Amp Return
#13
I tried two different 741's and couldn't tell a difference. They say the vintage RCA's used in the originals sound better, but I'm willing to chalk that up to mojo horseshit. I don't have two pedals to A/B, so there may be subtle differences with various chips. I did try a RadioShack poly film .056 cap before using the "tropical fish" cap pictured above. Again, without comparing two pedals, I didn't notice much of a difference. Nothing on the PCB jumped out as seeming like low quality parts, but if you have the means, go for it.
#14
Quote by Jason43
I tried two different 741's and couldn't tell a difference. They say the vintage RCA's used in the originals sound better.


Yeah, I heard the same thing about the 741. I think the original had germanium diodes? I've been collecting schematics and PCB layouts from around the net. The problem is what do you trust as accurate to the original grey 250?

Here are some PCB and Layout graphics (by MarkM) of the old grey but don't know if they are faithful to the original pedal:

http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Grey+OD-250+LAYOUT.png.html

http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Grey+OD-250+TRANSFER.gif.html

I post this because I'm considering making a clone replica of my own, if possible, and/or modify my existing YJM308 per your instructions.

[EDIT] - (I think I'm going to start a new thread about cloning a 250 so I don't get beyond the scope of modding the YJM308 here)
Fender Malmsteen Strat > Boss NS2 Noise Suppressor > NS2 Send > NeoClassic 3080 Compressor > NeoClassic 741 Overdrive > NS2 Return > NS2 Output > VHT Special 6 Ultra Amp > Amp Send > MXR Carbon Copy Analog Delay > Boss RC3 Loop Station > Amp Return
Last edited by Yngwie#1 at Jan 7, 2010,
#15
Can anyone help me with this quick and stupid question, one of my cables split and i am not sure where it goes, its a red cable which goes from the batterry, should go there near the green and white cables which connect to that 9v input?

Here is a pic.

Ibanez GRG270BKN
Bugera 6262-212
YJM308 Overdrive Pedal
Boss-GT10
#17
Quote by Jason43
Now, if you think you have the sheer testosterone to mod the PCB, read on. There are several traces you need to cut before you install the op amp. When the op amp is on the pcb, the pins are laid out like this:
1-----8
2-----7
3-----6
4-----5

Flip the PCB over to the soldering side. Remembering that the pins will be reversed with the board flipped over, cut the trace that runs between pins 5 and 7, the trace that runs from pin 8 to R5, the trace that runs from pin 1 to C5 and the trace that runs off of pin 6(be careful not to break the trace it connects to). Solder in the IC socket. You will then need to run a bit of wire from pin 6 to the top of R2(use the top hole from the C2 cap you removed for this) and run a wire from pin 7 to the top of R5. See the picture if none of this nonsense makes any sense. Insert the 741, making certain it sits in the same orientation as the 4558 was. And just like that, you’re done. Put you pedal back together.




Hi, just to verify the PCB trace cuts, can you look at the illustration I made below and tell me if I have the cuts (at the red ellipses) in the correct location? I'm not 100% sure where you had cut from pin 1 to C5 becuase of the T-intersection there? Note that the view here is reverse of your photo as it is looking through the board from the component side:



Thanks!
Fender Malmsteen Strat > Boss NS2 Noise Suppressor > NS2 Send > NeoClassic 3080 Compressor > NeoClassic 741 Overdrive > NS2 Return > NS2 Output > VHT Special 6 Ultra Amp > Amp Send > MXR Carbon Copy Analog Delay > Boss RC3 Loop Station > Amp Return
#18
A note about my PCB trace layout above. Instead of altering the original YJM308 PCB, I am going to make a new PCB for myself with a modified layout that gets the pedal back to true grey 250 specs. This will include the 5 pin angled molex connector so it will be easy to swap it in or out.

Anyway, when I get confirmation of the trace layout modification questions above and complete the altered PCB layout I will share it here if that is okay? Here is what I have so far for an modified PCB to work with the different 741 IC pinout. I noticed on someones picture of the Analogman 741 mod, they add a jumper wire from IC pin 1 to IC pin 6? Please verify I didn't goof up the connection from IC pin 6 to where capacitor C2 used to be. I removed the C2 pads completely here:



I am using the free ExpressPCB program and could supply the pcb file too if you want. I don't advise using their service to order custom PCB boards because the minimum order is for 2 boards, and that would cost you around $36 per board. You could buy a new YJM308 or 250 pedal for that. It would only be practical for large orders if you were selling "original design" pedal kits or something.

Legal-wise I guess it would be okay for anyone to make a slightly altered PCB replacement for their own YJM308/250 pedal? But no one should sell these as a subsitute PCB to retrofit the YJM308 or re-issue 250 pedal, because of the subtle changes it is not a brand new original PCB layout design.
Fender Malmsteen Strat > Boss NS2 Noise Suppressor > NS2 Send > NeoClassic 3080 Compressor > NeoClassic 741 Overdrive > NS2 Return > NS2 Output > VHT Special 6 Ultra Amp > Amp Send > MXR Carbon Copy Analog Delay > Boss RC3 Loop Station > Amp Return
Last edited by Yngwie#1 at Jan 20, 2010,
#19
I've got a stupid problem with that kind of pedal - black wire connected with bypass through a capacitor split, and i have no idea, where i should solder it.
Can anyone help me?

A pic:
#20
That looks like a resistor. Did you buy that pedal from someone or did you change the original footswitch? That's not the original one.
Fender Malmsteen Strat > Boss NS2 Noise Suppressor > NS2 Send > NeoClassic 3080 Compressor > NeoClassic 741 Overdrive > NS2 Return > NS2 Output > VHT Special 6 Ultra Amp > Amp Send > MXR Carbon Copy Analog Delay > Boss RC3 Loop Station > Amp Return
#21
Quote by Yngwie#1
That looks like a resistor. Did you buy that pedal from someone or did you change the original footswitch? That's not the original one.



this, someone may have put that there at the attempt to get rid of any popping noise when they click it on.
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#22
I don't think the original SPDT switches pop, at least it doesn't in my stock YJM308. I'm not familiar with that brand switch layout he has. In my own 250 clone I used a Cliff 3PDT switch in a different wiring configuration that grounds the PCB input (the diagonal wire) when in true bypass and didn't need any pull down resistor:

Fender Malmsteen Strat > Boss NS2 Noise Suppressor > NS2 Send > NeoClassic 3080 Compressor > NeoClassic 741 Overdrive > NS2 Return > NS2 Output > VHT Special 6 Ultra Amp > Amp Send > MXR Carbon Copy Analog Delay > Boss RC3 Loop Station > Amp Return
Last edited by Yngwie#1 at Aug 3, 2010,
#23
Ah, trv, resistor, i ****ed it up '^^

Yup, I did buy the pedal from someone (and it was working at the time). Could you find a way to fix it from context?
#24
Hi, I'd like to put LED light on my YJM308 just to see if the unit is On or Off. Need you your help guys, pls give me wiring diagram.
#25
What great direction and great thread. Thanks. Question. I have the same PCB board as shown above. It's in a 250 Reissue. I modded the IC socket (didn't go the full trace cut route) and swapped out the opamp (1458). I also swapped out the diodes. Now I have two issues. There's a capacitor in C2 labeled "25". C3 is 0.01uf and C1 is 0.056 uf so inline with your grey mod specs. I have no idea what C2 is. Any thoughts? I also heard that if I want to increase gain I should lower the value of one of the resistors. My problem is that it seems the resistors in my reissue don't match what I've seen online. the site told me to reduce R6. I can't tell which resistors are the feedback resistors (worth playing with) and which are the impedance or voltage resistors. Any thoughts?

Thanks.

steve
#26
The 25pF C2 is not needed if you switched to a 1458, which is just a dual 741 inside and has the same pinout as the 4558 used in the reissue Yellow and YJM308. You are basically in gray spec once you remove that too. You probably didn't have to swap out the 1N4148 diodes since they were on the late 70's gray, but earlier grays did use a different diode.

I'm not allowed in this forum to post the link (or any link - I almost goofed again) to Analogman's YJM308 mod page but you can Google it. He explains the parts and and says DOD added C2 to smooth the high end of the 4558 chip. It wasn't on the original gray or original yellow 250. But this may help you. Here is a chart I made to document the different 250 versions and part differences:

Fender Malmsteen Strat > Boss NS2 Noise Suppressor > NS2 Send > NeoClassic 3080 Compressor > NeoClassic 741 Overdrive > NS2 Return > NS2 Output > VHT Special 6 Ultra Amp > Amp Send > MXR Carbon Copy Analog Delay > Boss RC3 Loop Station > Amp Return
#27
What would I have to do to lower the amount of gain in this pedal.
Last edited by Notrik82 at Nov 27, 2010,
#28
How would using 1n34a in the DoD 308/250 clipping section effect the clipping.
Has anyone tried asymmetrical clipping.
Or a switch for symmetrical/ asymmetrical clipping?
#29
I got a little DIY mod fever today. Needed a fast easy little project. Thanks so much for describing how to mod this pedal.

Modded my DOD YJM308 Overdrive to late 70's gray specs. Removed stock KA4558 chip and replaced with socketed LM1458N (dual 741 op amp), removed C2, and replaced 0.001uF C3 with 0.01uF. Done in less than 30 minutes!



Finished off my DOD YJM308 Overdrive late 70's gray spec mod with original DOD style fluted knobs! Sounds freaking great now just like the gray DOD 250 clone (Neo-Classic 741 Overdrive) that I built from scratch last year.



I've been meaning to do this for some time. Only thing 'optional' I could add is true bypass 3PDT footswitch, LED, and Boss style power jack, and re-decal it to say YJM250.
Fender Malmsteen Strat > Boss NS2 Noise Suppressor > NS2 Send > NeoClassic 3080 Compressor > NeoClassic 741 Overdrive > NS2 Return > NS2 Output > VHT Special 6 Ultra Amp > Amp Send > MXR Carbon Copy Analog Delay > Boss RC3 Loop Station > Amp Return
#30
hi im sry this would be my first mod so i would have some questions i dont know if im looking it right but i dont get where to cut the traces if you could take a nother picture or help me to understand the istructionsi would be very happy pls lol apart from that i dont have any questions thanks again