Wednesday, 28 May 2014

Rothwell Switchblade

There's a partial schematic up at FSB, missing all non-polarized cap values. I thought it would be a nice idea to take a guess at them. The values i selected should take the sound close to the original unit. Of course, if any of you have better guesses on the values, let me know. This design has three clipping stages (not gain stages as PGS demo suggests) and overall footprint isn't your usual copy of a copy. There's a lot of gain coming out of a single TL072 too...



Posted by at 01:00
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18 comments:

  1. glasspak7328 May 2014 at 08:52

    what other diodes can we use for D1 D2 D5 D6. I have 4733A zeners,BAT 41 and BAT46 and some different germaniums

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    1. mirosol28 May 2014 at 09:04

      You could socket them and see what works best. I do believe 5.1V Zeners may be a bit too much, but it may be worth a try anyway.
      +m

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  2. Zick28 May 2014 at 10:10

    Thanks Mirosol! Been waiting for this one a long time. Almost bought the original. I guess it's wise too socket the non polarized capacitors...

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    1. mirosol28 May 2014 at 11:06

      Yup. Those are just guesses as i don't have an access to original unit to measure. I chose the values based on experience with other circuits. As the original is claimed to be fat and not too bright sounding, i tried to keep that in mind with my guesses. The 100n caps from 1K8s to ground could be a lot bigger ones too.. 470n or even 1µ would be a good thing to try on those spots...
      +m

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    2. Zick30 May 2014 at 19:23

      I have built this today and it works and sounds quite nice. Really hard to say if it sounds just like the clip but I can say it sounds like a good high gain overdrive without very much highs(in a good way).

      I do have oscillation problems but those disappear when I place a buffer in front of it My input and output cables are still quite long so that might explain it. The tone pot is wired backwards in the layout.

      The gain pot gives a low continuous sound like the d string on the ninth fret of a guitar. This is most noticeably audible when the gain pot is fully closed(turned fully counter clockwise) but the sound is also in the background when the gain pot is further and fully opened. It can be heard when the strings are NOT played. Also, the sound of the effect(when the strings ARE played) is very strange when the gain pot is turned almost fully counter clockwise. It sounds like much of the highs disappear then and is a bit like the sound when you move a wah wah pedal towards your heel.

      Much appreciated! Hope that there's some further suggestions to solve the little problems.

      Delete
    3. Zick30 May 2014 at 21:15

      I just realised that it is not for certain that the gain pot is the source of the low continuous sound that I mentioned. I only know that it is most audible with the gain pot fully closed.

      Delete
    4. Zick1 June 2014 at 18:23

      I have socketed all non polarized capacitors so it's easy enough for me to try any suggestion in that area..

      Delete
    5. mirosol1 June 2014 at 21:30

      Sounds like it's oscillating in lowish frequency when the gain is closed. That could be any cap resulting in that behavior. Same thing with the high pitch squelch.

      I posted a request for the correct values on FSB. Let's hope someone can take some measurements from the original unit.

      Until then.. Trial and error with the values.

      I don't tag this one yet as the values do not seem to be correct.
      +m

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    6. Zick2 June 2014 at 23:24

      Ok, I'll just have to be patient. Not my strongest talent:)

      Delete
    7. mirosol26 June 2014 at 20:00

      Now there are better guesses up at FSB by mmolteratx. Layout updated. Should work a lot better now.
      +m

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    8. Zick28 June 2014 at 00:11

      Thanks! Just ordered the right values. Will probably be able to test Wednesday. I'll let you know.

      Delete
    9. hujiko29 September 2016 at 10:44

      Hello Zick, How did you connect the tone pot? Thanks and Cheers.

      Delete
  3. Zick2 July 2014 at 21:49

    I have just replaced the capacitors. Unfortunately now the only sound I am getting with the pedal turned on is a continuous beep... Thanks anyway.

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    1. mirosol2 July 2014 at 22:33

      Damn.. I'll make another request for the values. Those did look better on paper.
      +m

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  4. Zick6 July 2014 at 00:21

    Much appreciated Mirosol!

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  5. Zick18 October 2014 at 09:58

    Hi Mirosol, I am trying to gain access to an original Switchblade. Is there a way to measure the capacitor values without having to desolder one of the legs of the capacitors? Tx.

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    1. mirosol18 October 2014 at 10:45

      No. There is no way to get accurate measurements while the components are soldered in. And as the board on the original is made with SMD parts, the task will be horrible to perform. One could just measure them in circuit and make educated guesses based on those readings.
      +m

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    2. hujiko26 September 2016 at 07:35

      I´ve tried to built this schematic and it sounds but with too low volume. Level and tone pots don´t work correctly, Gain yes. Has anyone had this problem?. Thanks.Cheers

      Delete

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