DOD 250 Treble Boost Mod?

[nascarbean_97]

So I'm needing a trebley overdrive for quick, repetitive chugging (not metal), as I run my Carvin xv112 with huge amounts of bass because I think the amp itself sounds the best that way.

Anyways, I'm wanting to know if anybody knows what to do to turn the DOD 250 in to more of a treble booster to combat the bass.

Anybody have a recommendation on which caps to switch to what values? I'm using the vero below.




Thanks!

[Steve Mavronis]

The stock DOD YJM308 is a more treble ended version of the 250 if you can find one of those or a layout.

[nascarbean_97]

Okay, sweet, totally blanked on that one!

Thanks!

[Mark Hammer]

Because of how gain is set in the unit, C2 and R2 set the low end rolloff at 720hz when the gain is maxed.  If you run a second RC network in parallel with R2/C2 you can produce additional boost in the top end.

Gain is set by the ratio of [R1+R2+pot]/[R2+pot].  So if the 500k pot is set to half resistance, the gain is equal to [1M+4k7+250k]/[4k7+250k] or 4.9x.  Trun the pot down to 50k and the gain is not (1M+54.7k)/54.7k = 19.3x.  And so on  When the pot = 0 ohms, gain is 1004.7/4.7 =  213.8x.

At the same time, because there is a cap in there, the low end rolloff changes along with gain, or rather the total resistance of the pot and the resistor in series with it.  At pot=250k, the low-end rolloff is equal to 1/[2*pi*R*C] = 1/[6.283*.2547Mohms*.047uf] = 13.3hz.  Drop the pot resistance down to 50k and that turns into a rolloff at 62hz.  Drop the pot resistance to 10k, and the rolloff starts around 230hz, and finally at max gain, the rolloff starts around 720hz.

Place a 2k2 resistor and .039uf cap i series with each other, and put that in parallel with R2/C2, and you'll have two paths for setting the gain, each with a different corner frequency.  With the pot set to zero ohms, the second pat with provide for a gain of 455x for content above around 1.8khz.  If you want that boost to be decreased a bit, make the resistor 2k4 or 2k7.  If you want the point where the extra boost comes in to be lower, make the cap bigger.  For example, a 2k4 resistor and .047uf cap would produce the extra top end gain around 1.2khz at max gain.

[nascarbean_97]

Okay, thanks so much! That's awesome.