This Week on the Breadboard - ROG Britannia

music6000 said:
The 4th band catches alot of Members out!
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I tell ya what gets me is the brown and red in low light. 1k/10k....

Chuck D. Bones said:
This is not a troubleshooting thread. If you want help with troubleshooting, please post in the Troubleshooting forum. Provide the following info:
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My bad. I usually will dabble with your mods and thought this might be a good place to ask about how the gain is. Didn't realize ROG had a separate sound sample page. I got it sorted. Anyway, didn't mean to derail your thread. I had already popped my board but did go ahead and remove the 100n by the treble. Agreed on the brilliance control as well!
 
An update. I was on a Vox kick and some of the other Vox-in-a-box* pedals didn't do it for me. So I rebuilt this one and found a few more things to tweak. I added a bright switch at Q1 for some extra sparkle. I reduced the BASS pot to 25K because there was only about 1dB of change from 7 to 10 with A50K. I increased the BRILLIANCE pot (I prefer to call it PRESENCE) from B100K to B250K and reduced C10 from 680pF to 510pF. A little more range in both directions. But the big mod was putting a 50K trimpot in series with D5 & D6 so we can raise the headroom and adding a MASTER VOLUME pot to the last stage to further increase the clean headroom. It is now possible to play clean without turning the guitar volume way down. I recommend setting the Headroom trim to 50%. If you want more crunch, then turn it down a bit. I tried putting a booster in front, but to me it was overkill. Do not omit R26. Mine oscillates when LEVEL is dimed and R26 isn't there.

ROG britannia - cb mod v1.2.png




* Vox-in-a-Box by Dr. Seuss
 
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Hi Chuck,

I'm wondering if in August '25 you used J201 for Q2 and Q4 and the drain/source resistors from the schematic above? Or did you use SK193 & SK193 like earlier?
 
I use J201's for Q2 & Q4 in the breadboard build of the version shown in the schematic in post #22. The DC voltages shown are consistent with J201 measured specs. The particular devices I used required the R9 & R15 values shown. If I used different J201's, it is likely that I would have has to alter R9 and/or R15 to achieve the desired operating point. See notes 3 & 4 in the schematic.
 
Finding J201 transistors that biased up with the given resistors went pretty quick. The 2N5457 was harder. I tried 50 SMD equivalents and only four or five went over 5V. One of them went up to 5.8V. It has a pretty high Vp of a little over -1V. So I decreased R3 to 3K65 and that was that.

The pedal sounds pretty good. I never played a Vox, so I don't have a frame of reference. But my guess is that the pedal could indeed sound like one.

Top Boost, no kidding. The pedal can take your head off with that treble. But with the Treble and Brilliance (Presence) knobs you can reign it in, no problem. Note decay is quite nice for a pedal. Knob ranges are really decent.

It's a fun pedal, 100%. Thanks ROG & Chuck!
 
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