Hi!
It's been more than a year since our last project was released. We are finally ready to share our new circuit, BRITANNIA, which is an overdrive inspired by the Vox AC-30 Top Boost amp, and a major revision of our previous work, the English Channel.
Hope you like it!
link: www.runoffgroove.com/britannia.html
Awesome. Thanks man, I love your projects, certainly some of the best in the effect community, and injected into the diy community as readily as you do is priceless. Thank you!
+1 to runoffgroove.com
Looks interesting, and nice demo from Jon.
This is the first time I've seen diodes before fets like this. Very interesting! I look forward to breadboarding this.
Quote from: commathe on March 06, 2014, 06:43:37 AM
This is the first time I've seen diodes before fets like this. Very interesting! I look forward to breadboarding this.
http://www.runoffgroove.com/azabache.html
QuoteThis is the first time I've seen diodes before fets like this. Very interesting! I look forward to breadboarding this.
Take a look at the links below,
http://www.sugardas.lt/~igoramps/article68/article.htm (http://www.sugardas.lt/~igoramps/article68/article.htm)
http://www.pat2pdf.org/patents/pat5619578.pdf (http://www.pat2pdf.org/patents/pat5619578.pdf)
mac
Thanks guys! ;D Those also look great
Well there goes my weekend.
Very cool guys, I'll be building this one asap.
Quote from: mac on March 06, 2014, 08:27:59 AM
QuoteThis is the first time I've seen diodes before fets like this. Very interesting! I look forward to breadboarding this.
Take a look at the links below,
http://www.sugardas.lt/~igoramps/article68/article.htm (http://www.sugardas.lt/~igoramps/article68/article.htm)
http://www.pat2pdf.org/patents/pat5619578.pdf (http://www.pat2pdf.org/patents/pat5619578.pdf)
mac
Those are good examples of diodes + transistors, but the ROG approach is (obviously) different.
ROG circuits sound beautiful. No doubt about it. Now, I must admit I don't quite get the logic behind using diodes to ground right before a supposedly triode-like FET stage. If their clipping is hard and symmetrical, why are FETs still required? Why not cheap and easy to find BJTs + asymmetrical diode clipping?
Quote from: Davelectro on March 07, 2014, 11:42:56 AM
Quote from: mac on March 06, 2014, 08:27:59 AM
QuoteThis is the first time I've seen diodes before fets like this. Very interesting! I look forward to breadboarding this.
Take a look at the links below,
http://www.sugardas.lt/~igoramps/article68/article.htm (http://www.sugardas.lt/~igoramps/article68/article.htm)
http://www.pat2pdf.org/patents/pat5619578.pdf (http://www.pat2pdf.org/patents/pat5619578.pdf)
mac
Those are good examples of diodes + transistors, but the ROG approach is (obviously) different.
ROG circuits sound beautiful. No doubt about it. Now, I must admit I don't quite get the logic behind using diodes to ground right before a supposedly triode-like FET stage. If their clipping is hard and symmetrical, why are FETs still required? Why not cheap and easy to find BJTs + asymmetrical diode clipping?
The diodes are there to keep the FET's from hard clipping. The diodes set the max input voltage and then the FET boosts that and possibly clips. If the diodes clip it's no major crime because they clipping will be masked by all the eq and gain stages going on.
Yes, I can see the LEDs are there to keep the fets from hard clipping. But my point is LEDs and regular diodes will clip hard too if signal is large enough. So we are sorta preventing hard clipping by means of (potentially) hard clipping.
The question is why in this case is hard clipping from the diodes more desirable than hard clipping from the FETs? I can only think the cumulative effect is key; the whole thing working like some sort of diode ladder under serious clipping.
Diodes to ground through resistors like 33k, 100k, 18k will hardly clip "hard".
I'm seriously thinking of building this circuit and using it as a preamp for a TDA7240. It would make a lovely combo with the 10" speaker I have here!
I wonder if there's a way to add a tremolo to this circuit...? Hmm.
Oh well, I guess it's layout drawing time!
Quote from: Lurco on March 08, 2014, 01:38:10 AM
Diodes to ground through resistors like 33k, 100k, 18k will hardly clip "hard".
But those Rs are not in series with the diodes. I see no voltage divider providing any extra softness.
Quote from: Davelectro on March 08, 2014, 07:33:15 AM
Quote from: Lurco on March 08, 2014, 01:38:10 AM
Diodes to ground through resistors like 33k, 100k, 18k will hardly clip "hard".
But those Rs are not in series with the diodes. I see no voltage divider providing any extra softness.
If you're talking about source resistors, they're not really involved in the diode clipping. Lurco was talking about the "grid stoppers", the resistors before the diodes pairs and in series with JFETs gates or the non-inverting input of U1a. The JFETs gates and the non-inverting inputs of JFET/MOSFET op amps have impedances so high you can say they're not there. So the only path to the ground is through those resistors and then the diodes (there is the 1M bias resistor on the op amp input but it's large enough to not count).
No, by Rs I meant "resistors", not source resistors. Sorry if I wasn't clear.
As far as I know, diodes to ground need some resistance in series with them to provide a softer clipping (since this resistance forms a voltage divider in conjunction with the source impedance + any resistance in series with the signal path).
And I'm not really sure about this, but at least from what I've seen in software simulation, large source resistances like 33K, 100K, 18K, etc. by themselves (NO divider) seem to make clipping start sooner, not softer.
Let`s take the first pair of 1N4148 diodes http://www.runoffgroove.com/britannia.png. There`s a voltage at the wiper of the gainpot, which will be roughly 3V maximum on its positive excursion. The 100k resistor and the left diode form a potentiometer for these positive 3Volts, where the "wiper" goes to the gate of Q2. According to the dynamic forward resistance http://datasheet.eeworld.com.cn/pdf/CHENYI/56576_1N4148.pdf fig.2, the lower half of the "potentiometer" will vary its value during the excursion of that max. 3V wave. At the max. point assume 3V divided by the 100k+dynamic forward resistance Rd of the diode (~2k @ 30µA), multiplied by Rd gives ~60mV at the gate of Q2. At lower values of the positive wave, the current through 100k+Rd will be reduced, and Rd will increase so that the "wiper" will go upward, thus reducing the "potentiometer"`s attenuation for lower input volumes. IMHO this describes an automatc gain control based on the curve of mentioned fig.2. This curve doesn`t show a sharp bend, and at larger inputs to the "pot" there`s but a low voltage across the diode.
For the negative half of the wave, the right diode takes over.
Where did I go wrong?
http://www.kennethkuhn.com/students/ee351/diode_characteristics.pdf
So hard clipping was not that hard after all. :icon_smile:
Interesting.
Thinking about building this for recording guitar jams/headphone amp. The sounds from clip 1 on the website sold me!
I see some shaping in the final stage, so would a ROG condor not be necessary on the output of this?
My hope is it would fit into my set-up like this:
guitar -> pedals -> britannia -> soundcard -> pc.
Or headphones instead of soundcard.
Glad you liked the clips; I feel like Gary outdid himself nailing those classic riffs.
Even though there is some basic EQ provided in the second output stage, it is not aggressive enough to replace a cab sim (either hardware or software-based).
Gary recorded some other clips going direct in that manner after he finished a build of Britannia using the PCB by 1776. Here's what he wrote:
QuoteI finished mine today. It sounds better than I remember and I remembered it as being pretty damn good! The touch sensitivity still blows me away. I decided to play around and the attached is the aftermath. Just wanking with the completed Britannia. The mindless doodling is not important. The item of note is the signal path. This is the pedal into a direct box -> soundcard -> convolution program using an impulse of a Vox AC30's speakers mic'd with an SM57. No EQ used other than the pedal. A little echo and reverb added after the speaker impulse. All guitars were a strat with a PAF-style bridge pickup.
I can post the clips if anyone is interested.
I'd be interested to hear those clips.
I have a condor breadboarded at the moment, once I've built up a Britannia I'm going to try to the following:
Brittiania upto u1a output, then condor t notch filter onwards.
Then if all sounds good, I'll double it up, add some dual gang pots, and hopefully finally have something to deal with my stereo effects chain...
How long, do you think, until a certain "booteeker" releases a pedal based on this? He'll name it something like "Britain Yeah" and put up a video on youtube where he'll explain how he fell in love with this amp and spent years developing the pedal.
Quote from: ubersam on March 27, 2014, 02:37:43 PM
How long, do you think, until a certain "booteeker" releases a pedal based on this? He'll name it something like "Britain Yeah" and put up a video on youtube where he'll explain how he fell in love with this amp and spent years developing the pedal.
I was just going to say the same thing! :icon_rolleyes:
Those clips sound VERY good,excellent job guys!
I think i love this baby!!!
In my search for the holy grail i think this is it!!
I've always been looking for that Rory Gallagher sound. In the early days of Taste, Brian May asked Gallagher after a concert: mr. Gallagher, how do you get your sound. Since then he used a Range Master on top of his AC 30.
I'll be ordering materials tonight en start etching tommorrow.
Hell i'm a newby here but i don't care lol
OK, the clips are now up at http://runoffgroove.com/salvo.html#britannia
Just wondering... What does the added A and C for the pots mean. Is A Audio?
My supplier has only Lin and Log, from Alpha though. Would this matter? And do i have to take Lin or Log?
Quote from: bilo01 on March 28, 2014, 07:23:00 AM
Just wondering... What does the added A and C for the pots mean. Is A Audio?
My supplier has only Lin and Log, from Alpha though. Would this matter? And do i have to take Lin or Log?
A = Log
B = Linear
C = Ani-log or Reverso Log
Thnx. Learned again
Wooooooowww. I just gave birth to this pedal and it really blows my socks off. It works from scratch and as a newbee here i like that very much.
I did no tweaking, lack experience for that, but man this baby sounds great!!! It's a must-build.
One issue though: at higher gain settings i've got a hiss, but haven't boxed it yet. Got to finetune the trims also but first impressions are very good!
Thanks guys at runoffgroove for sharing this!!
Hi all,
Looks like a another great project from ROG! I'm thinking about building it, mainly to be used with headphones use. What would be a good cab sim to build to go with it?
There are lots of suggestions here,
http://www.diystompboxes.com/smfforum/index.php?topic=100602.msg885730#msg885730
but I'm not sure which one is the most suitable for the character of the Britannia. Should it match the speakers of the AC30?
You may have to rename this if these damn Scots get their way this week!
Quote from: StephenGiles on September 16, 2014, 03:04:14 AM
You may have to rename this if these damn Scots get their way this week!
??? Is Sebastian Scottish?? ;) I don't believe that Britannia includes Caledonia.
Quote from: bluebunny on September 16, 2014, 08:40:12 AM
Quote from: StephenGiles on September 16, 2014, 03:04:14 AM
You may have to rename this if these damn Scots get their way this week!
??? Is Sebastian Scottish?? ;) I don't believe that Britannia includes Caledonia.
Moi? I'm from a different hemisphere :-)
Quote from: StephenGiles on September 16, 2014, 03:04:14 AM
You may have to rename this if these damn Scots get their way this week!
What about The Welsh? :icon_mrgreen:
mac