Another finished Britannia...

[Lee Oswald]

I finally completed the vero layout. That was more labor than the G2D or a full Klon. Well, okay maybe not the Klon.

I'm going to be int minority here. It's merely okay. It reminds me of the Boss BD-2 in many ways. It has the spitty decay and harmonics zinging around all over the place. It seems to make a great rhythm OD, but I'm not real impressed with it as a single note/solo OD.

I think I may try the English Channel. Or maybe I'm not a pseudo Vox kinda' guy. I wonder if I bias the JFET's a little on the cooler side if it may not suit my ears a little more.

[Chris60601]

Heya Lee

Happy to hear you made it through the Britannia. The English Channel is nice also. Perhaps not as "bright" as the Brit.  I am also in the build phase of the Galileo (another Voxy-type) that looks, err - sounds promising.

I nearly finished it - I am hung up on not having a .68uf cap. I was like, you have to be kidding! One stupid part away from a complete build-before-boxing...

So a trip to the local "Shack" with the hopes (or shall I say, there is probably a better change that it will snow today, a foot, in less than an hour - have the sun come out later, hit 80 degrees to melt it, AND have a full eclipse viewable all before 6:00 pm tonight).

But yes, I tend to agree, the VOX sound isnt for everyone I suppose. I like too many. Good thing there are amp-emus. I'm certain that if the wife doesn't leave me due to this hobby - I know for certain that if I came home with a VOX, A Twin and another Marshall - that would certainly do it

... Hey... Wait a minute...

[Frank_NH]

Hey Lee,

I used the 1776 Electronics PCB so that made my build a little easier.  Sound wise, it's one of the better ones I've made.  Make sure you dial in those JFETs - I wasn't noticing any spitty decay in mine.  However, it can be bright, but I think that is an advantage for humbucker guitars.  Of course, if you want a different vibe, there's always the Azabache .

I've been on a Hiwatt kick as well recently.  Finished the Model H a while back (which is FANTASTIC) and will next tackle the WIIO.  I can then have a Hiwatt shootout, but I'm betting the WIIO will be good too, so it will be a hard choice.

My goal is to develop select set of foundation drives for gigging, and I can see having Marshall, Hiwatt, Vox, and Fender amp sim pedals on my pedal board for different songs, with maybe an overdrive or boost in front for some extra oomph.  We shall see...

[Lee Oswald]

Funny you should mention the EC, Chris. I was thinking i might like that better. Or perhaps the CB-30. Heck, I don't know anymore. i'm chasing a gritty open tone, as it will really suit the sound of the original group I play with. Maybe I'm barking up the wrong pedal.

Frank, I biased those transistors to precisely the voltages given by ROG, and that are on the layout. I noticed a startling degree of interactivity in the tone controls. That, and the fact that you aren't getting that ragged, spitty decay makes me wonder if I made a mistake somewhere. Everything works, so I wonder if it's possible that a resistor or cap off by one row could create what I'm hearing. Usually that sort of mistake means something doesn't work right, often that's the entire pedal. i suppose I'll have to check the values as well.

*SIGH* here I go again! I'll post any findings.  

[Frank_NH]

I have to say that, in my experience so far, the JFET based amp-sim circuits have a greater chance of being "spitty".  Perhaps it's the way they are biased.   Op amp circuits tend to be "smoother", though this is not universal.  I'll go back and listen to my Britannia more closely - it may be "spitty" at some some settings, but that may depend on the guitar, pickups, etc.  I didn't notice anything unusual when I was rocking out.

In the long run, you should seek a pedal that appeals to your playing and gear.  So keep trying different circuits.  I highly recommend the Model H and plan to build the WIIO (and eventually the Model G).  Perhaps one of those would work for you.

[Frank_NH]

Here's a nice demo of the Britannia...

Britannia Demo

I will try to record some demos of mine when it's boxed.  Stay tuned...

[Lee Oswald]

I've been unable to post the last few days, but here is a development.

I had a sense, as I referred to previously, that one or both of the JFET's were biased too hot. So I made some adjustments to Q1. The 82K/18K were brought down to 47K/2.7K. Man, that made a whole world of difference. It still sounds like a Vox, if that's important to someone, but now it doesn't sound like a Blues Driver Vox.

I've thought about further changes, such as making the .0022uF cap from Q1's drain bigger, and either making the 470pF bypass cap on the Gain control bigger, or maybe just removing it. Making the 47pF cap to ground before Q4's source bigger, possibly MUCH bigger.

Just food for thought.

As to amp sims being spitty, I've only had experience with two others. The Azabache, and the Umble. Neither of those were spitty, although I didn't keep either of them. They just weren't something that sounded good to me. But ROG seems to have modified their M.O. and now they seem to be motivated to remain excruciatingly rtue to the amps they are simulating. Just my perception, and nothing more.

[Lee Oswald]

Meant to mention this to Frank -

I noticed the spittiness, or weird decay on chords as they ring out. It was present on single notes, although not as prominent.

[Frank_NH]

Hi Lee,

I assume you meant Q2 for the 82K/18K voltage divider mod.  Interesting change - I need to research that configuration with a BJT emitter follower (which is acting as a buffer to drive the tone stack), but reducing the effective drain resistance should reduce the gain.  There is another way to reduce gain, however.  Simply delete the 10 uF source cap in parallel with 50K trimmer.  That will cut the gain by about half.  I did an experiment recently with the ROG Supreaux circuit, which sounded too woofy.  I eliminated the 33 uF source bypass cap at the first gain stage, and that did the trick - the overdrive was much smoother.  Anyway, that idea may be something to try with the Britannia.

As for the 2.2 nF cap off the first gain stage, you can increase this to get more bass frequencies through.  The 470 pF bypass cap retains treble as you reduce the gain, so you could eliminate this with no harm (and even put it back later right on the pot lugs).  I don't think changing the 47 pF cap before Q4 will have any effect except to rolling off treble as you increase it.  I would just leave that one alone.

As for spittiness (is that word?), I have tested my Britannia on a SS amp and it sounds OK.  Do you use a tube amp?  If so, is it pretty clean?  Britannia is not meant for tube amps on the edge of breakup.  It is not an overdrive in the sense that it causes your amp to go into musical clipping.   I think it sounds best through a clean amp, preferably a solid state amp (or even a PA).  Of course, you still may not like it, and you may find other circuits out there that do the AC-30 thing better.  For me, I think the Britannia is a fine effect.  To be honest, I'll probably use it to achieve one kind of sound with my guitar (e.g. something like the Edge's overdriven sounds on early U2 records), and use other pedals for more Fender, Hiwatt or Marshall-like sounds.

I have a PCB for the ROG Umble so I'm going to build that up in the near future. Stay tuned...

[Lee Oswald]

In no particular order -

I do use a tube amp, but I *AM NOT* of the school that likes them on the edge of break up. I'm a pristine clean amp sort. I've noticed over the years, that certain speakers will bring out certain things in drive pedals, depending on what frequencies the speaker is reproducing.

Yup, I meant Q2.

That was *exactly* the idea with regards to the 47pf cap before Q4. The more the gain goes up, the more harmonics go flying all over the place.

But with the changes to Q2, I don't see the need to make any other changes. It sounds great now. Does it sound like an AC-30? It's very close. It sounds like one, but doesn't have something that a cranked AC has that is felt in the hands, how the amp responds to touch. But it sounds excellent, and I'll use it because it sounds really good, but not because it sounds like an AC-30.

[Frank_NH]

Thanks Lee for the input.  I may try that Q2 voltage divider mod after I get more time with the Britannia (just two resistors - should be easy to desolder).

BTW - I assume you retained the J201 at Q2?

[johnk]

hmm. I have ZERO spitty decay on mine. IME, it's imperative that that the jfets are selected and biased properly in all Jfet designs. otherwise you won't have the pedal sounding/working correctly and will not like the sound of it at all.

[Lee Oswald]

Well, the jfets are certainly biased properly, that's easy enough. But what is meant by properly selected?

[johnk]

even if Jfets's have the proper bias, it doesn't mean that they'll all sound the same.

[Frank_NH]

"Even if Jfets's have the proper bias, it doesn't mean that they'll all sound the same."

This is quite true.  Depending on Idss and Vp for the stage, your gain can vary a bit and that can affect clipping in later stages.  That's why I think you should always measure your JFETs so that you can get repeatable results.  If you're interested I'll post the Idss and Vp for the JFETs in my Britannia.

[Lee Oswald]

That would be greatly appreciated Frank.

Would this require the jFet matcher or can it be done with a DMM that tests for hFE. I am pretty sure what the answer is, but thought I should ask to be sure.

[rocket88]

You need the jfet matcher, the DMM won't do it, nor will the DCA55 or DCA75.

[Frank_NH]

Lee - just build this little JFET tester (use circuit #2):

http://tagboardeffects.blogspot.com/2012/07/greatly-improved-jfet-matcher.html

It's very easy to use.  Switch one way to get Idss and the other to get Vp.  Note that for Idss, the value in mA = voltage reading x 10 (e.g. if the voltage reads 0.063 mV then the Idss = 0.63 mA).

BTW, just use a SPDT switch on/on (no center off).  I also have a switch for the 9V power.  So the test procedure is:

(1) Insert JFET (make sure the leads match the pinout of your JFET)
(2) Attach the +/- leads to your DVM (alligator clips or whatever works for you)
(3) place switch to the Idss mode
(4) Switch on the power
(5) Record Idss value
(6) Switch to Vp mode
(7) Record Vp
(8) Label the JFET for future use.  I use ordinary masking tape and mark the FETs with a letter A, B, C... which is then recorded next to the readings above in a spreadsheet.  If you want you can give your JFETs nicknames - like flamethrower - so you can say "I used flamethrower in my Umble!".

Yes, it takes some time to go through a bag of 50 FETs to measure and label them, but it's worth it, especially if you're wondering what JFETs to use in an upcoming build.
 

[Lee Oswald]

I'll be building the tester in the next few days, but wanted to ask. What were the numbers for Idss and Vp that you used? Why did you choose those specific values?

Thanks!

[Lee Oswald]

Built that improved matcher, was hoping I could get the Idss and Vp numbers from you Frank.