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Thursday, 27 July 2017

VOX MKIV Tonebender

Description of the MKIV origin from the captain.
 
The origins. Tone Bender MKIII, Tone Bender MKIV. Same party different frock. Aside from the obvious differences in the enclosure type of these pedals any true solid definition of which is what in regards to circuit type is and will always be a little bit of an ambiguous subject. The way I always made sense of it in my head was in regards to the biasing. The early MKIII's were choppy, heavy, clumsy, a fuzzy lump hammer. The later MKIV's were smooth, dynamic, articulate, a distorted boxing glove. In between, you have a foggy transitional period. Even with the those definitions in place it never always runs true.





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28 comments:

  1. The Great Gaze28 July 2017 at 11:20

    This comment has been removed by the author.

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  2. Travis28 July 2017 at 14:10

    It's been here for years
    http://tagboardeffects.blogspot.com/2012/04/sola-sound-tone-bender-mkiii-3-knob.html?m=1

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    Replies
    1. Zach28 July 2017 at 16:56

      Didn't realize tech Vox and Sola Sound were identical, thought there were some component differences like some of the other tonebenders.

      Delete
  3. Travis28 July 2017 at 18:31

    The one that I linked to is what you would call a MKIII if you're going along with DAM semantics

    The layout here is what you would call a MKIV in DAM semantics

    The difference is the biasing of the darlington pair.

    This is identical to the one that you labeled MKIV except for 2n2 vs 2n which is a negligible difference

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    Replies
    1. Zach28 July 2017 at 19:30

      huh, did not notice. i found a bunch of tonebender schematics and just started making/modifying layouts. but, yea a 2.2nF vs 2nF wouldn't make much difference. probably should have run them by you first since you are the resident tonebender expert.

      Delete
  4. Claudio29 July 2017 at 00:44

    What hfe should be the Best for the 3 tránsitors?

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    Replies
    1. Travis29 July 2017 at 01:39

      Most people do the first two like 40-80 and Q3 90-150. It's a pretty wide range and it doesn't have to be high hfe to sound good

      Q1 and Q2 low leakage is good, for Q3 you want some leakage

      You're going to want to at least experiment with the transistors, the Ge diode, the 2n cap, and the 220K resistor.

      The 2n cap is crazy bright and thin, depending on your amp it can be kinda annoying and useless. I recommend 4n7-10n instead.

      The 220K drops the output level. I normally omit this and wire tone 2 directly to volume 3. You could use a smaller resistor too, but most people will not like the 220K resistor there

      With those things sorted out nicely this circuit really sounds amazing. I like this version the best but it is what people call the MKIV and it's the same as the other MKIV layout

      Delete
    2. Travis29 July 2017 at 01:41

      To be specific for those that want to know, when you see 680K that's what "they" are calling MKIV

      Delete
  5. BlueOysterCult10 August 2017 at 08:37

    I built it but I was not successfull..
    I Checked everything twice but I did not see any mistake.
    Used AC132 with HFE 70-80-130 (I supposed that Q1 Q2 Q3 were from left to right)
    I supposed that output was volume 2.
    Thanks

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  6. Travis10 August 2017 at 14:11

    The 680K needs to be moved to Q1 base

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    Replies
    1. Zach11 August 2017 at 05:38

      thanks. made the correction on this and all the others.

      Delete
    2. BlueOysterCult25 August 2017 at 11:48

      Ok works great now. Thanks

      Delete
  7. pakkee6612 August 2017 at 15:57

    Started built and found to be 23x8 board, thanks for the layout.

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  8. pakkee6612 August 2017 at 21:48

    Successfully follow the advice in the comment, omit the 220k and up the tone cap to 8n2, Q1,2 ac128 hfe100/200 Q3 3ax31 hfe115, [no fuzz when q1,2 the gain too low on my board] I like it sound so much, thanks to Mr.Travis the tips and Mr.Zach the layout, share some photos here: https://goo.gl/photos/CDtsPTtNXancNE3N9

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    Replies
    1. mirosol13 August 2017 at 08:32

      I've built tens of these with the original layout. The way i've done the volume fix is to have 250K pot for the volume and replace the 220K with 82K. This way the overall resistance between the tone stack and and ground remains close enough. This means that the knee of the high pass filter created by the volume pot doesn't change when compared to the original circuit - and you'll still have way more volume.
      +m

      Delete
    2. Travis13 August 2017 at 16:41

      That's a great suggestion. I have tried various resistors and A/B tested between a 100K resistor and no resistor for example and to my ears the only noticeable difference is the output level. If I set the volumes to match, they sounded the same to me. So I have been a fan of no resistor based on my own testing, though I encourage everyone to experiment for themselves

      Delete
    3. Travis13 August 2017 at 16:48

      Pakkee - You needed to go way too high on the hfe because you didn't correct the placement of the 680K resistor.

      Delete
    4. pakkee6614 August 2017 at 23:57

      oh, I used the old layout, thanks Travis, I'll fix it soon, and try the 250k pot/82k mod by Mirosol's suggest, and the tone cap 8n2 was too much low end to me, down to 6n8 will good to me, thanks for the help sir.

      Delete
  9. pakkee6615 August 2017 at 10:11

    yeah~ 680k in the right place now, after test with some Ge, end up Q1,2,3= 50,70,135.[50 on Q1 seems better for clean up], 1n270 is the best or 1n60 is good too, and I keep my 8n2 tone cap, it just fit for me now~ thanks again Travis for pointing me.

    ReplyDelete
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    ReplyDelete
  11. Unknown7 September 2017 at 00:06

    Hey, wondering what to do about the negative voltage (-9V). Because my power supply only has +9V. Can I use +9V instead?

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    Replies
    1. pakkee667 October 2017 at 16:05

      you use -9v supply only on this board, or you can build a daughter board like this: http://tagboardeffects.blogspot.hk/2013/02/ne555-voltage-inverter.html ,so you can run in +9v supply.

      Delete
    2. pakkee667 October 2017 at 16:09

      or this more simple Negative Voltage Inverter: http://tagboardeffects.blogspot.hk/2012/05/negative-voltage-inverter.html

      Delete
    3. Zach7 October 2017 at 19:38

      you can use a +9V power supply. just connect the +9V to the ground on the board and the ground to the -9V.

      Delete
    4. pakkee6614 October 2017 at 22:50

      I'm so stupid to built the inverter everytime for my pnp fuzz, and never thing about this way..thanks for the mention, and sorry about my answer, shame..

      Delete
    5. mirosol15 October 2017 at 09:06

      Do note that you can't daisy chain other pedals with negative ones. The inverter is a good way to go...
      +m

      Delete
  12. Unknown26 December 2017 at 21:47

    I got "GT402V / AC128 USSR Vinage Germanium PNP transistor" off ebay for the transistors. Thought it would be cool to have older ones and wanted to try it out. But my circuit is not working, zero sound. Im getting -9V and I have triple checked my connections and orientations. The only thing I can say would be different is that I am using non-polarized electrolytic caps and I did not use soldering sockets on my 1N270.
    Thanks!

    ReplyDelete
  13. Chesterton16 May 2019 at 10:17

    Built with AC188k trans and sounds incredible.

    I made some mods:

    - Used 1n60 germanium diode
    - Swapped 220k resistor to 22r
    - Swapped 2nF cap to 8n2
    - Swapped 6,4uF to 8.6uF

    Great sound!, thanks to zach!

    ReplyDelete