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DOD250 Vs. YJM308


 
3/13/2003 12:17 PM
pef
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DOD250 Vs. YJM308
Does someone know the difference between the stock DOD250 and the YJM308 (DOD250 Yngwie Malmsteen signature) ????  
 
Does someone have one of this and can open it to trace the schematic ?  
 
Thx.
 
3/13/2003 4:03 PM
Mark Hammer
Check the schems at Aron's stompbox forum. Both have been posted. The difference is in a few component values. Quite frankly, the differences are so subtle, they shouldn't make much difference, and may only be preferred if you have the exact same rig.
 
3/13/2003 8:18 PM
elgorgon
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The YJM is the same circuit as the original "Yellow" Dod 250 but with a .001uf input cap (vs. .01uf on the original). Please correct me if I'm wrong, but I believe that would make a significant difference. I'm not sure on the original "gray" 250.  
I put a .1uf input cap in my modded reissue, which has significantly more bass response than stock.  
Also, the reissue 250 has a 100k resistor feeding the clipping diodes; the original and YJM have a 10k.
 
3/13/2003 9:02 PM
Mark Hammer
You're not wrong at all. My shrugging off the component value changes was imply because it isn't really anything you couldn't do with a tone control or a bass cut earlier in the signal chain. The 100k resistor change also l cut down the amount of clipping, but again this is something easily compensated for driving the pedal harder or softer.  
 
I am not suggesting the changes are deceptive. Rather, they just provide a way to tailor the existing design to the circumstances that the particular player works in - a convenience if you will. If you don't have the same guitar, strings, signal chain, etc., the few component changes will be far from enough to produce the same sort of sound. Conversely, if you have a different but highly flexible setup, it should be a piece of cake to duplicate with a variety of different pedals.
 
4/5/2003 9:13 AM
Soren
Here is my contribution on this matter:  
 
This is a great simple circuit to start understanding the electronics for guitar sounds.  
 
Yep, the difference is just a couple of capacitors, and the output series resistor. The input capacitor, and the capacitor on the op amp feedback loop near the gain pot. Changing either capacitor to larger values will give more bass and midrange. The YJM 308 is setup to sound more trebly, like a treble booster with distortion! It actually sounds more darker or mid scooped also, again that's because the capacitor values are smaller than those in the DOD 250.  
 
For those that complain about the hiss from the YJM 308, you can do some type of mod to reduce the treble. What might work is a small capacitor attached to ground right after the 10k series output resistor. Since a lot of gain is coming through here due to the low value 10k as opposed to 100k, a cap right here might be the ticket to bleed off some treble before hitting the diodes. Mark Hammer, what do you think of this mod ?  
 
Or for less distortion and thus hiss, simply snip out the darned diodes! I love that! This makes the sound smoother, more natural, and a little louder because the signal is not being clipped.  
 
By the way, you can get this box to crank out volume by changing the output volume pot to a higher value. This prevents the signal from bleeding to ground because there is more resistance to ground now with a higher pot value. The same theory applies to a guitar volume pot, the higher the value, the more signal gets through, and is thus louder. One reason why I don't use any volume pot at all in my guitar! Preserve the signal all the way to the amp input.  
 
If anyone is feeling experimental, you can get it loud enough to plug it straight into the power amp input, bypassing the preamp for a different sound,(the new Marshall 1987x has an effects loop). But now you don't have any tone controls. What I do, is use a pro 15 or 30 band EQ! The input of a pro EQ needs a stronger signal than the input of the guitar preamp, so you need to use a larger value volume pot to drive it and the effects loop return jack (power amp input).  
 
What I don't like about this box is the circuit traces are thin and come off easily with the heat from soldering, so be carefull, or better yet, build a point to point maximum quality stompbox with good quality resistors and capacitors. Avoid any electrolytic capacitors if at all possible, use polypropylene capacitors.  
 
Best regards,  
 
Soren
 
4/5/2003 9:45 AM
Soren It's Really A Gain Cut Knob!
Another issue to contemplate about the DOD250 and YJM 308 circuits:  
 
The volume trick also works for the gain pot, but in reverse, since it is in a negative feedback loop around the op amp. The smaller the pot value, the more gain and volume you get. This is because the more signal bled to ground, the less negative feedback is produced. It is dumping the negative feedback. Less negative feedback = more distortion, really! The circuit is naturally very high gain without a gain knob there, it is there to bring the gain down under control. So it should really be called gain cut and not gain boost. So there goes any marketing hype! This box goes to 11 because it actually goes down to negative 1! It is just wired so that gain increases when you move it clockwise. In other words more negative feedback causes less distortion, just like the power amp section of a guitar amplifier.  
 
Now you can see how this simple circuit can lead you to bigger and better ideas by applying the theory to something else, like the negative feedback loop in the Marshall 1987x! For that, there is a series resistor, nothing going to ground usually, so just increase the resistance for less negative feedback for more distortion from your power amp.  
 
Thanks,  
 
Soren
 
4/8/2003 2:12 AM
Soren This Box Goes To Negative 11!
:)
 
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