Runoff Groove Britannia (AC30 emulator) -- hot off the press!
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- čas přidán 27. 08. 2024
- The Britannia is Runoff Groove's redesign of their English Channel, a Vox AC30 with Top Boost emulator. The circuit uses a combination of FETs with mild diode clipping between each stage, and a really neat power tube emulator with LED soft clipping in the feedback loop of an op amp at the end of the circuit. It does touch sensitivity very well, cleans up with the guitar pot, and both the low-gain and the high-gain settings sound excellent to me, without fizziness and with a very natural decay.
The tone controls are as on the amp (though a couple work backwards):
Brilliance (cut): This cuts the treble after the preamp section. (This is backwards from the amp in the pedal)
Bass: This is a fairly standard bass cut control. (Also backwards from the amp -- probably because it would have had to be a rare pot value [50KC instead of 50KA])
Treble: Simultaneously cuts bass and boosts treble and upper midrange.
Overall the circuit retains treble extremely well without getting too noisy. There is a mild bass cut even at "flat" tone settings, but not severe enough to translate to the video. This is as in the top boost channel of the amp and is probably related to the size of the coupling cap after the first stage; I believe the same mod as on the English Channel could simulate the normal channel or jumpered.
Like the Azabache, this is a much more sophisticated circuit than the predicessor ROG circuit it "replaces", and there are all sorts of cool things in it, including a cabinet simulator. Although I think I prefer the Azabache for the lower gain sounds and because its EQ is more what I want to hear, I am extremely impressed with the Britannia and plan to use it on an upcoming recording.
I highly recommend building this one. Runoff Groove has a 1590BB perfboard layout available, and I've included my own perf layout for a 1590B in my perfboard library available on my website. There is also a PCB layout by Ian Birdsall (and I imagine more to come).
Huge thanks to Runoff Groove for sharing their design! :)
Gear used:
Runoff Groove Britannia
Don Quixotecaster with Reilander custom pickups
Tone King Imperial
George L's cables
El Capistan (dotten eights setting) for "I Will Follow."
Songs played:
The Waiting (Tom Petty) - low gain/jangle
I Will Follow/Where the Streets Have No Name (U2) - medium-high gain with delay
Driver 8 (REM) - high gain, high treble setting "dirty clean"
Forgive any playing mistakes, I just learned the riffs and I film the whole demo without cuts and splices!
The reason that this pedal retains that sweet creamy treble is because it uses lower values for the op-amp gain; a 10k and 1k in the feedback loop, instead of the 500k or 1m that we typically see in common overdrive or distortion pedals. These lower values also affect the impedance, and amplification is all about impedance, controlling your gain stages, and filtering. The gentle gain and frequency filtering that is incorporated in the first several FET gain stages in the front end, also contribute to the Britannia's voice. If you want to add some fire to this gem of a pedal... simply add a 1uf or a 10 uf (the larger the value on the capacitor, the deeper the voice) across the 1k Q4 Source resistor (add a 5k pot in series with the capacitor to make it adjustable) or add a 100k pot in series with the (above mentioned) 10k op-amp bypass resistor. This is the resistor that is right below the two clipping diodes on U1a of the Britannia's schematic. Doing so... will allow you to slowly dial up the heat.
Thanks for all your help all the time with my builds on the forum. Your the best and I really appreciate you passing down some knowledge. You really know your stuff that's for sure!
Always the best demos. Excellent job and I dig the new pedal.
A new ROG design, what a welcome surprise. Thanks for demo'ing, Jon.
Love all your FET pedal demos Jon. Let's do this new type of FET emulating to other famous amps.(I mean this type of diode-before-JFETs emulation!)
Great demo, John!
Nice demo, Jon, as always. Props on the "Driver 8" quote.
This buddy knows his tunes!!!
Also, great demo!
AS always, great playing and fantastic build execution. Cheers and regards from Cortexturizer
jonspatton very nice, here is my take on that pedal: Britannia - Vox AC30 Top Boost - Demo
Excelente
Hi.. Jon Nice demo mate :)
But I wonder if Britannia is good when stacked with other pedals.
Such as and overdrive like tube screamer, boss sd1, etc.
Could you be kind if you have time hehehe... demoing Britannia with and overdrive pedal. I want to know how it sound
thanks
I believe one of the demos on the ROG site has it stacked with another overdrive or fuzz. I've loaned it out and I don't usually do more than one demo of a pedal, so you might be waiting a while. It's definitely boost-friendly, though.
Do you know if there is a PCB available for a single width pedal like the one in this video, or just the double width one linked on the ROG site?
I built this on a perfboard layout I made from the schematic. It's in the perfboard library on my website, jonpattonmusic.com. It will require testing the FETs beforehand as it doesn't have trimpots. However, the 1776 Effects PCB project and the original ROG layout are only 1590BB-sized (and they have the trimpots). So far as I know, there aren't any other layouts for this.
could one use this by putting it into the effects loop return jack of an amp, thereby bypassing the amp's preamp? would that work especially well?
+Iggytommy I don't know about "especially well." It also depends on whether your effects loop bypasses the tone controls; if it doesn't, there's not much point in my mind.
jonspatton I believe effects loops on an amp usually occur after the preamp including the EQ. That's the case with my amps anyway.
To bypass your amps pre/tone controls try going into pedal, out of pedal, into return of fx loop... That should bypass your preamp and tone controls on many amps.
Sorry man the only thing I can clearly hear between the ON and OFF audio samples is the noise of the pedal. No significant difference in the sound, in the best first almost half of the video, which is probably YT and computer speakers. Now when you crank things up yes, it sounded nice but at an unacceptable amount of noise. Not sure what's going on with your setup, but if that's how the Britannia sounds then it's a non practical pedal. Otherwise, kudos to you, very nice, tasteful, playing indeed! Btw, I always thought RoG designs became progressively very over-engineered, I have tried a few of them in a simulation scenario and -sorry guys- they did not make the grade. Cheers, anyway!
Hi Jon,
Could you use this pedal direct into a PA?
I think this and the other ROG amp sims are made to be run that way. I used the Azabache that way a few times, but I don't think I've ever used this direct. The sound samples on the ROG site though are direct I believe.