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Sunday, November 20, 2022

GARY HURST: Tone Bender MKI - Castledine, 0.15" Vero

I wasn't aware of this version of the MKI until today.  I'm sure you have probably seen the new line of Tone Benders that Sola Sound is releasing.  I noticed that the Stu Castledine version was on vero, and the rest were all on the more familiar MKI board. 

So after a little digging, it turns out this is based on a very early Tone Bender that Stu has - so early in fact that Gary Hurst said that it was rehoused from one of the original wooden enclosures.

Here's a link to a site that Graham Green used to run, talking about the providence of Stu's MKI.   The excerpt below, as it is quite a long article.  Graham has several original MKIs and is a keen collector and historian of early guitar pedals (British in particular).

Of the wooden ones though that’s very different!! To the best of mine (and Garys) knowledge, (as well as many many contacts with similar interests) this is the last complete original example. A friend Stu has one that has the same board but clearly re-housed in an early prototype metal case (with no battery Hatch – Gary acknowledges that to be the case with that particular pedal) 

GARY HUSRT MKI TONE BENDER - CASTLEDINE 0.15" VERO LAYOUT


UPDATE:  After taking a close look at the values on a Reverb listing (images below), I've updated the layout and MKI component table.  It clearly has 22n input and output caps, which is certainly a detour from the usual 10n in and 100n out.    

Despite the relatively small output cap, it still sounds fat.  22n and 33k = ~220hz roll-off as opposed to 100n and 47k coming in at ~34hz.  It starts with more bass input care of the 22n and a larger coupling cap on the second stage, so it has less to lose on the output.   I tried a 100n and it sounded too woolly in the low-end.

Worth noting that the 100n and 8.2k usually found before Q3 has a roll-off of ~194hz.  The larger 25u and 8.2k has a roll-off of less than 1hz.  So basically things even out somewhat by the time it reaches the level pot.  This does of course lead to a different tone, as all three transistors are receiving more bass in this version.   


CASTLEDINE MKI PHOTO CARE OF REVERB



note the 22n input & output caps



I believe the output resistor is 3m3 instead of 2m2 - maybe to trim some level off, as this doesn't have a resistor across the 500k pot.







MKI VIDEO DEMOS





MODDED MKI TONE BENDER LAYOUT

I trimmed the layout down and spaced the components out, as I had a piece of vero this size to use and the one above is a little cramped.  






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Location: Balmoral QLD 4171, Australia

16 comments:

  1. Mister HateNovember 20, 2022 at 11:21 PM

    Just this weekend I build a couple adapting the Zonk Machine original vero layout.
    (1 Tone Bender MkI and a mix between a Supa MkI and a MkI with just one knob for the Volume and with an output cap).
    For the next one I will try this layout.
    Have you ever take a look at the Carlsbro Fuzztone?
    https://www.freestompboxes.org/viewtopic.php?t=27766

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    1. AndrewNovember 21, 2022 at 8:37 AM

      Cool. Sounds a bit like my weekend.

      I haven’t tried the Carlsbro. Thanks for the reference, I’ll give it a try - looks interesting.

      Delete
  2. ClassicFuzzJanuary 12, 2023 at 9:50 PM

    I just finished your modded layout. Verified and it sounds amazing. A really really raw and nasty MKI. I love it!

    And I just saw your wiring layout. I will try that one too as soon as I get one of the original enclosures. Thank you for all your amazing work! :-)

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  3. AndrewJanuary 13, 2023 at 5:57 AM

    Great. What transistors did you use?

    I’ll probably add some photos to the layout a bit later. I’m mounting the vero above the pots almost the same way that is done with the more well-known poor to point layout. Basically a couple of heavy wires from the board to pin 1 of each pot to float it above the pots.

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  4. ClassicFuzzJanuary 15, 2023 at 9:27 AM

    This time I used GT404, although they often tend to be a bit too leaky.

    Something I wanted to ask. What is the gain range of the OC75s?

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    1. AndrewJanuary 15, 2023 at 12:18 PM

      I only have about ten OC75 left, which are all Valvo pulled from an old Australian telephone exchange (wish I had access to more). They have a pretty broad range - anywhere between 90 - 150 hfe with leakage around 400 - 500 measured on my little multi-function tester. By comparison, my OC71 sit around 60 - 80 hfe with leakage around 400 or a bit lower. In circuit they will work anywhere an OC75 is needed for leakage, but they will be a tad less aggressive sounding due to the lower hfe - this is usually only a minor difference.

      Delete
  5. Mister HateJanuary 16, 2023 at 9:56 PM

    The OC75 I have/used are from different manufacturers (Valvo, Mullard, unknown) and they measure usually in the 50 to 200hfe (but I used one with 15hfe that I used as Q2 in a germanium fuzzrite that sounded glorious) and the leakage are all over the place too, from 100ua to 700ua. A bit like OC71 but with more gain usually.

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    1. AndrewJanuary 17, 2023 at 6:40 AM

      I’ve had the occasional outlier as well - almost very low hfe and insane leakage. One was so bad my tester thought it was a diode - it still worked in a circuit.

      Delete
  6. ClassicFuzzApril 16, 2023 at 11:40 PM

    Thanks for the update. I'll try the new version asap. I was just wondering, if the 3.3Mohm resistor is necessary or if I could keep the 2.2Mohm resistor. What does this resistor do?

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    Replies
    1. AndrewApril 17, 2023 at 7:45 AM

      Hello - you can still use 2m2. This resistor helps reduce the output level, as MKIs as extremely loud without it. It makes a difference to the level, but no change in tone.

      Delete
    2. ClassicFuzzApril 17, 2023 at 10:06 PM

      Thanks! Made the changes (except the 3.3M resistor) and sounds better than before. I like it. :-)

      Delete
    3. AndrewApril 18, 2023 at 6:38 PM

      Yep, it’s pretty nice sounding.

      Delete
  7. ClassicFuzzNovember 14, 2023 at 5:57 AM

    Correct me if I am wrong, but I just realised that when I don't build it like Stu and instead mount the pcb to the pots, I have to connect the rows 1 & 2. Otherwise I am getting lots of extra noise bleeding in. I tried this with 4 different versions and they all have less noise and crackling sounds.

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    Replies
    1. AndrewNovember 14, 2023 at 6:01 PM

      Interesting, have not noticed that myself. Will have to try it one day.

      Delete
    2. ClassicFuzzNovember 15, 2023 at 12:15 AM

      I was getting crazy as I thought most of my transistors were noisy. But fortunately that bridge cured it all and now I can use any transistor pair I want without unwanted sizzling :-)

      Delete
    3. ClassicFuzzNovember 15, 2023 at 4:50 AM

      I forgot to mention, I always build mine NPN with an isolated power supply (no battery). Maybe the bridge isn't necessary when building it PNP with a battery.

      Delete

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