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Want to Moddify boss OD1


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9/19/1996 9:46 PM
Robert
Want to Moddify boss OD1
Hi  
I have a boss OD1 which I hate the sound of. I think it sounds thin and nasty. Is therea mod or component subs I can make which will make it sound more like a overdriven tube amp?  
 
Any advice is much appreciated.  
 
Cheers
 
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9/20/1996 12:50 PM
Mark Hammer

Most overdrives that use op-amps (and this will include almost  
everything that isn't an obscure mid-60's Japanese fuzz-box) have a similar  
structure to them, which lends itself to a number of dependable interventions.  
For example, I find the MXR Distortion+ to be a particularly annoying unit  
(although my amp speakers roll off at around 10khz instead of the more typical 2-4khz, so the high end is more irritating through my amp). A small value  
capacitor straddling the input to the VOLUME control and ground takes out  
most of the sting and "rounds off" the sound. It doesn't give more "chunk", but lets whatever chunk is there seem more apparent in relation to the "buzz".  
Alternatively, it may be that you want to take some of the high end off at the *beginning* so that the overdrive adds harmonics of lower-order harmonics  
instead of harmonics of higher-order harmonics. You can accomplish this by  
rolling back your guitar tone-control, but then bypassing the OD unit leaves you with a mute-sounding instrument, so that may be a non-starter for some.  
By identifying the first op-amp in the signal chain within the OD unit, and placing a HF-limiting cap in the feedback loop (i.e., between the output of the first op-amp and the input), you can tame the high-end grit and get a smoother overdrive. If you can identify the capacitors which the signal passes through on the way to the output, you can sub slightly larger values to give a lower rolloff frequency at the bottom end.  
A somewhat different strategy it to replace the "Drive" control with a  
smaller value pot and put an additional resistor at the input to the pot so  
the entire range of the Drive control only covers a small portion of the possibilities (see below). This lets you fiddle with the Drive and dial in just the right amount of overdrive to your taste. The down side is, of course, that  
the overall output level would be limited.  
 
Pot (e.g. 10k) (Total R = value of Pot, e.g.4.7k + 4.7k)  
 
IN -----/////-------- GND IN----///-----/////---GND  
^ or NC ^ or NC  
*OLD*
 
10/25/1996 6:26 AM
G M Arts

Another mod you may like to try is that the "soft-clipping" diodes in the Boss OD-1 are not the usual pair of back to back silicon diodes (in the negative feedback path of the first op-amp). Instead, Boss have places 2 diodes in seies, then those 2 in parallel with a 3rd diode facing the opposite way.  
 
(I'm not sure how this will come out on your browser, but here's an attampt at a drawing)  
 
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