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previous: Robert HiI have a boss OD1 which I hat... -- 9/19/1996 9:46 PM

Re: Want to Moddify boss OD1

9/20/1996 12:50 PM
Mark Hammer	Re: Want to Moddify boss OD1 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

9/20/1996 12:50 PM

Mark Hammer

Re: Want to Moddify boss OD1

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*

Replies:

G M Arts Another mod you may like to try is ... -- 10/25/1996 6:26 AM