Friday, 6 July 2012

ROG English Channel

Info from the Runoffgroove website:

The Vox AC-30 amp is considered by many to be the defining sound of the British Invasion during the 1960s. The Top Boost circuitry provided crisp treble-laden overdrive that perfectly complemented the rich bass content. The English Channel is a JFET-based distortion stompbox that uses the same basic architecture as that classic early '60s amp.

This circuit is based on a 1961 Vox AC-30 with Top Boost, as designed by Tom Jennings and Dick Denney. Artists such as Tom Petty, Brian May, the Rolling Stones, the Beatles and the Shadows have used the AC-30 during their careers.

The above schematic replicates the Brilliant input, but the Normal input can be simulated by changing the 470pF cap to 47nF.
(A DPDT switch to select either 470p or 47n sounds like a good idea to me for a possible mod - Mark)

To obtain 1.6v at the source of Q4, you may need to try different J201 or adjust the 4k7 resistor. During testing and development, values as high as 12k were necessary for some J201. Try to get close to 1.6v, but slightly lower values will have no audible difference.

Note that the Cut control is set up in the traditional manner, reducing treble as turned clockwise.

Philip Miller Tate (a.k.a. Ge_Whiz) found the Cut control to be quite subtle when using the stock values. He reports that substituting a 47nF capacitor and 50k-B pot provided a much more effective control.






I, mirosol, added the following: I just recently built one of these again, and noticed that couple small things could make it even better. Not that there's anything wrong with it as it is, but - i used 50K trimmers for more accurate biasing of the JFETs, linear pot for Treble, swapped the Cut pot lugs and made it 50K with 47n cap, bigger Master pot for sligtly more overall volume and the switch for Brilliant/Normal channels. The 470p felt way too thin, so 1n/47n combo on a switch sounded perfect. I also moved things slightly around to get the switch in neatly, plus i added the polarity protection diode.. Here you go. My slight mods for this, very, very nice sounding Vox in a Box.


59 comments:

  1. Wtf happened to the causality 4??????

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    1. Don't worry it's still there. There's been a couple of people who built it without success so I'm going through it tonight and want to keep it on hold until I can either confirm the layout is definitely correct, or make any required corrections.

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  2. Built this already with a switch for brilliant/normal :) JFETs are still not my friends.. :( I have only something like 30 of J201s, and i've been swapping them around for some three hours :)

    Only way i could get close to 1,6 on Q4 source was to lower that 4K7 to 3K3. All my voltages are close to ROG's, with exception that source voltages on Q1, Q2, Q3 and Q5 are a bit high. About 5 times higher...

    When all drain voltages are at 4.3V - 4.6V, i get pleasant low oscillation, but nothing more. I get no signal past the circuit.. I went the board through with magnifying glass (literally:)), and it seems to check out against the layout. I didn't compare it to the schem yet though...

    It's almost 3 in the morning here, so i think i'll just try to debug just a little, tiny amount of time more...
    +m

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    1. With it being you, I'll assume the layout has an error! I'll check it over and let you know if I spot anything. Cheers bud

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    2. :D

      Somehow i hope that there is :D

      I'll get some sleep and continue in the morning.
      +m

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    3. Yup! :o) Cut 2 and 3 should be on the 5th row, not the 2nd. Let me rejig it.

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    4. Thinking about what that does though, I'm not entirely convinced that will be the cause of the problem. All that correction does is move the Cut pot from one side of the 1K5 resistor to the other before Q5 gate and it doesn't look like it would make that much difference. I can't see anything else but I'll go over it a few times in case anything else pops up.

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    5. Don't know how you count them, so i'll just for a word. I was a bit concerned about the source voltages, as they are 4-5 times higher than the ones on the ROG's baseline voltage list. They are still under 0,4 - 0,6 for all of them. Oscillation changes pitch with pots, and cut did nothing. Cut connected wrong could have something to do with it.

      If you can, please see if there's a way to fix the current board, Those were my last 100K trimmers :)
      +m

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    6. The layout above shows the change but you can do it by just soldering the cut wire anywhere on the 5th row in the spare holes on the left hand side, in between the 2n2 and 15n or under Q5. That's the only issue I've spotted so far.

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  3. I`m having similar issues to Mirosol, except the oscillation is far from pleasant. drain voltages are 4.51-4.57 for the relevant drains sources are roughly double rog baseline values but these are on a par with my perf build which works fine (after the fifth build :-() also getting a fair bit of hiss,

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  4. meant to mention that my cut pot appears to have an effect, cut 2,3 on row 5.

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    1. I'm starting to wonder if this is one of those that are not ment to happen... :)

      I'll leave it for a while and do something else.
      +m

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    2. The only other thing is that I reversed the order of the 1M and 10n from the 1M & 1K2 junction at the top mid/right (it should be 1M to the junction followed by 10n to ground). I didn't think that would make a difference and so did it the opposite way because it fit the layout better, but if you can swap those two over it would appear to me to be absolutely correct to the schematic. Just take the top of the 1M down one row, and the top of the 10n up one row.

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    3. Definitely can't see anything else. Have you got an audio probe either of you, so you can test to see where the problem starts?

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    4. Starts at the input.

      Is that 100µF at the right place? Schem says that input touches only 33K and 1M, but layout has 100µF neg connected to input as well.
      +m

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    5. Haha, bingo!! Snip it mate, it should be going to ground, forgot the ground only starts after the 1M resistor! :o)

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    6. Yup. Did it. That fixes it. Now.. It does really need the power filtering, otherwise it squeals really bad. I'll use wire and some shrink wrap to get it to ground... Then it's back to tweaking the voltages :)

      I'll tell you once it's ready.
      +m

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    7. Layout corrected. It's just a power supply filter cap so you can omit it, or just find a space between 9V and ground to solder it in if you want it in there. This is typical, the only component on the board which doesn't appear in the schematic is this cap, so I didn't even consider it when I was checking through! :o)

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    8. You can tag it.

      I still have some problems with cut, but i'll sort that since it's my problem from now on :)

      Actually.. http://www.runoffgroove.com/englishchannel.png

      100µF power filter cap is in the schematic - first component on the upper left corner :)

      Sounds nice. There is really some real AC30 in there. Can't even compare this to joyo ac tone that i bought. A mistake. Ah. One needs to make mistakes to learn :) To everyone - don't buy it. It's not worth it. :)

      As this one goes, the scale of diffuculty.. On scale from 1 to 5, i'll give it 8. It's not impossible, but i surely wouldn't recommend this to anyone for their first build. It would be like recommending life long windows user Arch linux... :)
      +m

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    9. Cool, I'll tag it. This may be useful for you too: "Philip Miller Tate (a.k.a. Ge_Whiz) found the Cut control to be quite subtle when using the stock values. He reports that substituting a 47nF capacitor and 50k-B pot provided a much more effective control."

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    10. Yup. Did that in the first place. :)
      +m

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  5. Just built 5 of these and a deep blue delay, I seriously need to get a life ;-)

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    1. 5 English Channels?!? Are you insane? :o)

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  6. Nope but I've had 4 mates pestering me since I built my first 1and I now have a spare, I also expect not to be buying beer for a while ;-)

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  7. This really shines in louder volumes, and that 47nF is a must...
    +m

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  8. Deffo my favourite pedal, I've been pestered by my mates to build them one but it took me 5 attempts to build one ( perf board is not my friend ) so now I'll get some peace. I did mine with an on/on/on switch, 470pf in the centre position 47nf to one side and 220nf on the other, 220nf makes it a tad darker and is a nice option for the cost of a cap.

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  9. Ha! Just thought of it. 470p and 47n on a stomp switch! Then i could have channel switch to stomp on! Brilliant for leads and Normal for accomp. Perfect!
    +m

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    1. When i was much younger than today, a wild weekend usually meant getting wasted non-stop from friday to sunday... Nowadays, i'll just finish up 5 boxes :)

      http://mirosol.kapsi.fi/varasto/boxes/EnglishChannel.JPG
      +m

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  10. you really need trimmers to adjust the voltage right? i guess the diffrent 201 won't behave the same? only have 2pcs of 100k trimmers at home...
    thought that i could replace them with resistors. won't work aight?

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    1. It will.. But it's much much much easier to use the trimmers to get all four drain voltages to be exact 4,5V.

      You could use the trimmers you have to find out what is the exact resistance on each JFET and then use plain resistors. If you just guess the value, you won't get the sound right. It would be much cooler with resistors, but...

      Do that if you don't mind soldering and desoldering the trimpots.
      +m

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    2. If you socket the positions between drains and the 9V row you could bias everything with just one trimmer and then replace it with an appropriate value resistor as you go along.

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  11. Which capacitor does this refer to "Philip Miller Tate (a.k.a. Ge_Whiz) found the Cut control to be quite subtle when using the stock values. He reports that substituting a 47nF capacitor and 50k-B pot provided a much more effective control."

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    1. The 4n7 at the bottom right

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    2. Thought it was that one,but thought i'd check first.

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  12. i build this today and it sounds great! the cut control in my build isn´t subtle at all (using the stock values 4n7 + 250k) so i´ll leave that alone for the moment...
    btw: you shouldn´t bother too much about recommended drain voltages. in my experience adjusting those trimmers by ear makes much more sense as well as using them in all circuits that have jfet´s in them... (see my comments to the wampler black 65);-)
    thanks again mark for your wonderful work!

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  13. I built this tonight and it fired up on first try (after trimming the JFETS) and it sounds great!

    I think I'm ready for the Klon Centaur now... :)

    BTW, I'm using the stock values for the cut control and it's a bit subtle but very usable troughout the entire sweep so I like it the way it is.

    Thanks for the layout. Cheers!

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  14. Just finished this...

    https://lh6.googleusercontent.com/-_xGI-Bvn6as/UheEmMgVS-I/AAAAAAAABB4/Y0HpFnX_6Pk/w1029-h772-no/IMG_2854.JPG

    https://lh5.googleusercontent.com/-9QkN8zSBTtg/UheE26cDFtI/AAAAAAAABCA/7TVpcUE_sKU/w1029-h772-no/IMG_2855_2.jpg

    https://lh6.googleusercontent.com/-xE1QuFlZGfA/UheE_aRK_2I/AAAAAAAABCI/p5ta5xmTLZA/w1029-h772-no/IMG_2860.JPG

    https://lh5.googleusercontent.com/-XS5Q2y-UV0w/UheEc-qlm0I/AAAAAAAABBw/9Uh-Y0yI7iM/w1029-h772-no/IMG_2846.JPG

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    1. Yes, nice job!

      I did a similar Union Jack color schem with a dual channel "King of the Britons" build a while back

      http://img.photobucket.com/albums/v325/jallenshaw/Pedal%20Builds/HRMfront.jpg

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    2. Very cool! Are those 9mm pots?

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  15. Hey folks, I need a bit of help with my build. All drains biased to 4.5-5V (Q3 9.11V), all pots work fine but the volume pot introduces a delay that I can best describe as being a slapback when volume is maxed out ?!?
    Any ideas?

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  16. I've built 7 of these, 6 from this layout and 1 from the ROG perf layout, none of mine had any slapback type issues.

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    1. It's very strange. I'll try to record a sample of it tonight.
      Do you have one still with you?

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  17. Hi everybody.
    Acter building a Naga Viper and a SDD3000 clone, i have built this english channel.
    Unfortunately, it doesn't work.
    No sound a all.
    I dont really know what to check, because i am not a expérienced builder.
    I have biased the pedal, and i could have pretty easily the voltages at all drains, but the source at Q4 is only about 0,30 V, Very far trop 1.6 V.
    How could i correct that ?
    I a not sure, but my 100uf power filtering cap is maybe not good. May i remove it off the circuit for debugging purposes ?

    Could maybe someone provide me with somme more voltage data from his own build based on the veroboard layout.

    i will make some more tests and give you soon pictures and precise voltages.
    (I dont know why, but my multimeter measures today 14v from a 9v battery, so as with a 9v DC adaptator ??? )

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    1. Correction, the battery of my multimeter was dead , which explain why I measured 11-14V ! Now, I have correct value of 9.5 V for a brand new battery and 9.63V for my 9V DC alim bloc.
      It is not the solution of my problem, but a necessary step to have a chance to find something.

      Here as my values after biasing the pedal.
      DC alim : 9.63V

      Q1 : D:9.61 (new and BAD !!) / S:0.23 / G:0
      Q2 : D:4.24 / S:0.29 / G:0
      Q3 : D:9.62 / S:4.26 / G:4.5
      Q4 : D:4.82 / S: 0.23 / G:0
      Q5 : D:4.61 / S:31.9 mv / G:0

      It seems that I have a problem with the trimmer from Q1 (defect piece and/or bad soldering). I will check that first and see the influence on Source from Q4 (0.23V is a lot too low ?? I should maybe try other value for the 4k7 resistance ??)

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    2. Hi.
      I have corrected oone cut which was wrong, and checked many other things, soldering, schematic, ...
      It always doesn't work. No sound at all .

      I have biased the pedal and get correct values at all Q, except that source at Q4 have about 3V (with a 12k resistor).

      I am a the point to ask in which position have to be the potentiometer volume, ..., Master : 0% or 100% ???
      I have never done that before, and I am not sure of anything anymore regarding this schematic.

      I am not convinced that the biasing explain why the pedal produces no sound at all. I suppose at should at least have something, even only crackles or bad sound.
      I am lost in my attempt to make this thing work.

      Delete
  18. This comment has been removed by the author.

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  19. Problem solved.
    It works like a charme now.

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  20. Is the switch for Brilliant/Normal a clean/dirty channel type of thing?

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    1. it`s more of a normal/treble switch

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    2. Thanks. I kept looking through forums, and it seemed like everyone already knew what it meant but me, so no one explained it

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  21. I have built this and it sounds good, but I am not getting quite the breakup that the one in the video gets at the 1:00 minute mark. To get that sound, I have to have the volume maxed and turn down the Master appropriately. I'll play with it a little more. I biased the trimmers to get 4.5V at all four drains. Hmmm. I aslo used Miro's mods. The switch is extremely subtle.

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  22. Is it possible to replace the trim pots with metal film resistors? I read on a diystompboxes forum that you could, as long as you knew the drain current you wanted, which I'm not sure how to find for this pedal. Here's a link to the forum:

    http://www.diystompboxes.com/smfforum/index.php?topic=81973.0;prev_next=prev

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  23. Oh man. English Channel just went from my least favorite to my top 3. Notice the date of my last post above...after getting away from it for a year! I found that my bottom rail wasn't grounded. It's a little double jump coming off the long ground jumper. Missed it. Now it sounds great! I hate it when a pedal works, but isn't right. That ground jump made a world of difference! Lol!

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