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.





21 comments:

  1. Nice timing! I was looking for a MKIII layout not too long ago and noticed there wasn't one on here.

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

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  3. 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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    1. 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.

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  4. What hfe should be the Best for the 3 tránsitors?

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    Replies
    1. 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

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

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  5. 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. The 680K needs to be moved to Q1 base

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

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

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  8. 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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    1. 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

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    2. 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

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

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    4. 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.

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  9. 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.

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  11. 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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