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MoonWatcher
Bronze Member
USA
98 Posts |
 Posted - 09/07/2008 : 14:58:37
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Yeah - R50 is basically a fixed value of the "bass knob" on a Fender amp.
Some folks have put the values of C26/C34/C35/R37/R38/R50/R51 into software, so that they can reset the the filtering/rebreak the bandpassing.
If you're familiar with amps, here's the breakdown:
C26 - treble cap
C34 - bass cap
C35 - mid cap
R37 - fixed treble pot simulation
R38 - slope resistor
R50 - fixed bass pot simulation
R51 - fixed mid pot simulation
Yeah - I don't like the interaction of C17 and C19 with the altered R26. I'd personally rather play with C101, even though it's a pain to get at. But I may like my gain lower than others, as well. I suspect I do.
Even though the post-level op amp recovery stage is tuneable with active eq, I've found it to be very unnatural sounding if you adjust any of the components far off from stock. But I guess that you could replace R21 with a trimpot to try and hit a sweet spot. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 09/07/2008 : 16:39:03
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Let us know the final-final answer when you get there  |
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MoonWatcher
Bronze Member
USA
98 Posts |
Posted - 09/10/2008 : 21:26:11
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Well, getting closer, anyways.
I've dropped the biasing on the tandem FET pairs to the point where the op amp doesn't get overloaded. I can now max the drive without any splat.
I've also replaced the op amp with a 4580L, and it sounds a smidge better. Since it's only biased @ 6.8K, I guess it's not doing much, anyways.
Now the problem is that the pedal is too dark, and a bit grainy sounding. This is even with a pair of 2N7000's where the quad of clippers was.
I'm thinking about replacing the "Fender tone stack" with the OD-3's twin t.
Has anyone noticed that this pedal primarily runs on 8 volts? They use a tranny and a half of the op amp to drop the supply down.
I'm not much of an expert on back-to-back FET setups. Anyone here able to give me a crash course? |
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Dr. Bob
Moderator
Australia
6593 Posts |
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BluesDriveMonster
Copper Member
32 Posts |
Posted - 09/21/2008 : 17:57:06
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What'd the removing of the C16-18 do?
I don't have any components on hand right now...can i remove those without doing anything else and yield pleasing results? |
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MoonWatcher
Bronze Member
USA
98 Posts |
Posted - 09/22/2008 : 19:24:47
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C16 is the final link that makes the op amp at the end of the circuit into an active "tone shaper." It simulates an inductor, when used in conjunction with C9 and R21. If you pull C16, you basically get the bias setup with a TS or similar pedal.
C17 adds some highpass filtering - I find it to be crude and hard to tweak, so I just pull it.
C18 is a coupling cap that is necessary to get the signal through the circuit - you can't pull it.
You can pull C19, which is probably a good idea if you're pushing up the value of R26, since those two form a low pass filter. Or you can make it a smaller value to roll off less highs. |
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BD-2 mods?
