Saturday, 20 January 2018

Jext Telez White Pedal

"A boutique pedal homage to the unique onboard overdrive circuit in vintage solid state Vox Conqueror amps that George Harrison used on the White Album and other Beatles recordings. The White Pedal has four knobs that control volume (overdrive), gain (fuzz), treble cut, and a bass cut knob that acts as a mid-boost, while a fifth knob (the Yoko knob) selects the midrange frequency to boost for a parked wah sound"

Original FSB thread and schematic available here.
Schematic should be correct but it's not verified yet


82 comments:

  1. This actually sounds really neat.

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  2. Does anyone know if i can use a Fasel cup core as the inductor as I have a spare. Can't seem to find any info on its inductance.

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  3. Alex, you can't believe happy you just made so many people...
    Hoping to verify this soon, just waiting for the inductor to arrive !

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  4. I once gutted a dunlop wah to put in a Area 51. Is the inductor in the Dunlop fit?

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    1. I think the original uses a Whipple Wah inductor.
      Need to test others to see.
      They need to measure 500mH (more or less).

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  5. Thanks a lot ! Can you confirm C1 is 300n as in the schematic ? (currently ordering some parts needed).

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    1. The guy that reverse-engineered the pedal has measured 300nF.
      The original amp schematic states 1uF.
      Not sure which one is correct but I would go for the 300.

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    2. Ordered both. I will socket this in first time. Thanks again.

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  6. Hey I'm the guy that traced this. Anyone who builds one, let me know if you run into any problems and I'll see if I can confirm on the original pedal (I still have it disassembled).

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    1. Speaking for a lot of people, I would say : THANK YOU !

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    2. Thanks for the effort and sharing, Michael.

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    3. Micheal: Thanks for sharing.... can you check the Gain pot connections compared to your schematic? Just noting the difference in this Vero board and your schematic as I am looking to make up a PCB layout.

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  7. Are the gain pot pin connections reversed? Pin 1-2 should go to the cap/resistor and pin 3 to the BC538?

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    1. That's based on the schematic but the board connections looked reversed.
      Easy to swap anyway.

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    2. You're correct. I looked at the schematic and it doesnt show the PIN numbers ... the usual pins are reversed (3 to right of the sweeper) on the Gain, Treble and Level Pots. Bass is normal pins.

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  8. awesome. been looking for the schematic for a while now and this is the next best thing.

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  9. The trace cut at coordinate Y10 should be one row lower at Y11.

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    1. Thanks but I'm not sure which one is Y10 (no cut). I've found an extra cut that wasn't supposed to be there under the 220R resistor (L/25).
      Layout has been updated.

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    2. Use letters for the columns and numbers for the rows - starting from upper left corner.

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  10. If i use a 2 pin inductor does it go across the two left pins of the one shown in the diagram?

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  11. Ok, i tried that and it works using my Fasel cup-core inductor. The only problem is the volume is way, way below unity. Could this be my choice of inuctor? Checked the usual culprits and all seems fine.

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  12. I was wondering about the two 150nf and 56n capacitor. They are not in the schematic?

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    1. These are summed capacitance as the layout uses a SPDT mini toggle switch. The original used a rotary switch and could switch the capacitor values directly. Alex did some magic here and used capacitors connected such a way to work properly.

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    2. Awesome! Thanks for the explanation. Still not sure why such low volume then. I have some large axial 250mH inductors that i would like to try, how would i connect, in series or parallel?

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    3. Sorry, should have looked it up, same as resistance.

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    4. Do you have the same volume issue when the tone selection switch is in difference positions?

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  13. Hi all. I wrote a note at FSB about this circuit. I modeled it in LTSpice and compared it with the original Vox Conqueror preamp. There is, I believe, an error in the schematic - the 20K/22K bias resistors on Q3 should actually be 11K and 2.2K and the collector resistor upped to 1.1K. Based on my LTSpice simulations, it should work with 10K/2.2K for the base of Q3 and 1.2K for the collector resistor. There are some other differences with the original Vox preamp, but this change should at least get you a healthy output signal. Let me know if this fixes the problem. I have an idea of how this could be implemented at 18V (and model the actual preamp better) rather than the starved 9V supply of this pedal, but I'll need to break out my breadboard for that. ;)

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    1. Hi Frank, thank you for your thoughtful reply and circuit analysis. Please see my response at FSB.

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    2. Thanks for this Frank. So i changed the 22k for a 2k2, the 470R to a 1k2 and the 20k to a 11k. Unfortunately the volume level stayed the same. I reckon there must be something else amiss.

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    3. Hey Gavin!
      From the pictures the previous values seem correct.
      Try reversing the 10uF cap in the top left corner...

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    4. Just tried that again no difference. I was just audio probing and i'm losing signal around the 1k resistor, i think. I'll keep on probing and let you know more.

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    5. Thanks for trying that Gavin. I still think the 2.2K is correct, and there may be something else going on. Try audio probing the collector of Q3 and lug three of the treble pot. There should be a healthy signal coming out of the transistor preamp/distortion stage before it hits the tone stack.

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    6. I'm getting sound up to the right hand 2N4125 and i am getting it to the base of the 1k and the 47k, not getting any signal from the next 47k or any points on the BC548. Sorry if some of these aren't in the audio path my knowledge is still quite limited.

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    7. Getting good signal from Q3 especially the collector and treble lug 3 is good as well.

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  14. OK! Is the signal full and crunchy at treble lug 3? This should be the "raw" signal coming off the preamp/distortion. If that signal is good, then the trouble lies in the tone stack/MRB.

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  15. Gavin: Double check your trace cuts (assuming you are on the Veroboard)... the original post Alex did had a cut under the 220R resistor that was not needed there. If you made that cut - reestablish the trace.

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  16. Thanks Fever, i did build it prior to that discovery, fortunately i did notice and amend.

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    1. Hey Gavin!
      I put this on hold while Frank and Michael try to sort out the schematic.
      If you wanna try something in the mean time:
      reverse the second transistor from the right (2n4125).
      On the first transistor from the right (BC548) add one 1K5 resistor going to ground and one 2K2 going to the same row of the 20K, 47K and 1K (V+)

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    2. Alex,you haven't mentioned from where next to the BC548 to place these resistors. From collector?

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    3. Just seen Motters post on FSB collector it is. I'll try in a bit.

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    4. Ok, that made no difference in volume. I think it made the whole thing nicer as it was a bit harsh. I'm using a boost after it and amp up high so i can actually make out whats going on.

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  17. I've been checking in with this since it was initially posted, as I have a wah with fasel inductor that I want to do something more interesting with. Reading this and the thread over at FSB - looks like this one is still yet to be fully verified. One thing, while I'm trying to assemble components - the dark brown caps are all labelled with n but usually those oval brown caps are for the ceramic pF values. Can someone confirm whether the 68 / 100 / 47 / 150 dark brown caps in the schematic are nF or pF values?

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    1. Go with what's written. Visual representations might not be the most accurate every time.

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    2. The values are correct(nF). The type of capacitor (as long as it's not polarized) doesn't matter. I always use the brown ones when the cap spans two rows because they are easier to read.

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  18. Schematic updated @ FSB! Seems they've sorted out all of the problems now.

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  19. I'm pretty sure that the link grounding treble 2 shouldn't be there: think there should be a track cut between the 220u electrolytic -ve terminal and the 100n cap on its right on row 7, and the ground link moved to somewhere on the left hand side of this new cut. Otherwise aren't you just grounding most of the output with the treble pot acting like a volume control?

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    1. Well spotted. Link needs to be moved and it needs and extra cut.

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  20. That looks like perhaps Gavin's issue regarding the low volume. The circuit does not have Pin 2 connecting to ground.

    Gavin: Have you resolved your low volume issue yet?

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    1. No Haven't resolved yet. Will give this a go when i get home later.

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  21. Good news, that did the trick! Works, but i need to roll back some changes i did during debugging.

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  22. So, Mr. Horsburgh, is this verified?

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  23. Yes, as long as you make those changes. Hopefully, Alex will update the layout. I changed quite a few parts during debugging which i think has changed the overall sound. I'll roll these back later today.

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  24. I'm to the point of drilling my enclosure and wiring up. Other than the missing cut and re-positioning of the jumper I did not make any changes... so I hope to second that verification soon.

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  25. Ok, I redid the board from scratch and it is now verified. My BC548s from Tayda have the opposite pinout to that in the layout, so be warned. And it sounds awesome.

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  26. Gavin: Which inductor did you use? I have the red and yellow and am interested in how yours sounds - audio links?

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  27. I used the yellow Fasel. I'll try and put a sound clip up later.

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    1. This comment has been removed by the author.

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  28. Finally finished mine up... worked well on the first try. Sounds good. I'm using a Dunlop inductor (green dot) that I had kicking around, but I anticipate buying a good one and building this again with better components. I only had generic transistors (2N3906, 2N2222) and I'm wondering if it would make any difference if I used spec parts.

    Gavin... what kind of enclosure did you use? I've managed to fit it into a 1590BB but I really could have used a little more depth to make it less cramped (vertically). The original Jext Telez enclosure looks huge. I still need to paint, so I won't have this packed up for a couple days. I'll look forward to hearing your sound clips with the yellow Fasel. I'll try to post some as well.

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  29. Sorry, mine is unboxed. I have templates made out of thin compressed board that i got from packing material. They make great templates for wiring everything up. And i have enough to make them for a while. I just drill the holes for all top panel pots, etc. and judge were the dc and jacks go. Then i can take my time when it comes to boxing. Unfortunately, due to laziness and good old British weather means i have a hell of a lot waiting to be boxed.

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  30. No worries, Gavin. I was just curious to see if anybody else was crazy enough to box this into cramped quarters. The 1590BB is actually a great size enclosure, but I could use another .2 inches of depth to make things just a little easier. I'll probably get a 1590XX. It has a bigger footprint, but adds that smidge of depth that I want. The alternative is a 1590C, which is just too tall for my tastes.

    Your compressed board wiring templates are a good plan. If I had done that with this pedal, I might have arranged a couple things differently.

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    1. This layout could probably be modified to fit in a 125B box.
      Around 23 x 24.

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    2. Board mounted 9mm pots would really help

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    3. Hi All, New to the forum. Thanks for all the amazing work, I've gotten up to speed on this addictive hobby in a few months thanks to this site!

      I built this pedal first on breadboard, following the schematic on http://www.freestompboxes.org/viewtopic.php?f=7&t=28772&sid=4a4f0d264874bc888b28e8060fc24696&start=20#p268483, and then on strip board using a modified version of the layout above (my main mod was to put the Yoko switch and caps on a separate small board - since I had a 1P6T rotary, I added three extra options). It is an awesome pedal! I used all spec transistors, but I'm not sure it is necessary.

      I noticed a difference with the FSB schematic is that in the schematic Q7's E and B are linked. To accommodate that on the strip board layout, the cut directly to the left of E would then be moved left by one hole. Also, my inductor (Dunlop) has pins spaced more narrowly than in the diagram, so some people should be aware they may need an extra link and cut to accommodate that.
      I put this into a 1590BB (used Small Bear's white coated, so it looks close to the original!)

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  31. There was an extra cut that shouldn't have been there.
    The layout had been drawn for a Whipple wah inductor.
    Do a Fasel legs need 7 rows instead of 5?

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  32. According to IVIarks Crybaby layout Fasel inductors span 6 rows.

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    1. Just wanted to male sure. Gavin or Wad may be able to tell us.

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    2. Fasel does span 6 rows. I had to bend both legs in a tad to get it to fit across 5.

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    3. Cool. I guees, if laid down, it should fit in a 125B size box.

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    4. The Dunlop inductor I used pretty much fit the 5 rows that are in the layout. I had to bend one pin out a little bit, but nothing major.

      All painted and boxed up now. I'm getting some self-oscillation in the last 1/6th of a turn with the Gain pot. The fuzz is awesome at that point, but it oscillates if it does not have a guitar signal. I'll likely be building this again, source me a better inductor, and use some better parts.

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    5. Have you seen Frank's inductorless version of this pedal on the FSB? (http://www.freestompboxes.org/viewtopic.php?f=7&t=28772&start=40)
      He has made a video and I've already drawn a layout.
      The inductor could still be used but Q2, QD3 and Q4 (from the schematic) are not actually needed cause they are part of the switching system. Does it sound like yours?

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  33. I was going to post a video so that we could compare the sound, but after trying a couple different guitars with my build, I figure I need to work out my gain problem. I'm not getting the good fuzz without oscillation.

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  34. Hi all! Did anyone come up with a solution for the oscillation problem? I’m having the same drama... running after a buffer settles it down but loses a tonne of gain. I’d love to figure this one out, it sounds amazing when it’s not squealing like a banshee.

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  35. I'm also getting the oscillation issue if it's not running after a buffer. Mine was built with a Fasel inductor replacement for a Wah

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  36. I just built this today, and it sounds pretty cool even ---without---the inductor!

    That doesn't come in the mail until Monday!

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  37. The layout says 'Wha' inductor, but Google's auto-correcting it to 'Wah'... so who's right?

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